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View Full Version : 1991 chevy 1500 5.7 tbi erratic idle



tpulliam79
09-24-2008, 11:00 PM
I just purchased this truck and have put new plugs and wires, new iac, new coolant temperature sensor, new 02 , cleaned throttle body,. I am having issues with a jumpy idle especially in park or after sitting at a stop for a moment, no codes and it doesn't die, it did get better after iac and coolant temperature sensor. any ideas of what else could cause this?

mnstrjim
09-25-2008, 01:32 AM
Mass air flow sensor, clogged catalytic converters, thing aint breathin right. May check your altenator voltage also. It could be low at idle and higher when reved up, causing mis or week fire to the plugs. Where did you buy it, was there a dramatic change in alltitude?

gr8shot
09-25-2008, 08:47 AM
I bought a 454 (in my sig) thats doing a similar thing. I haven't figured it out yet either. I started unplugging sensors to see what would happen. I unhooked the electrical connection to the map sensor (back pass. side above intake manifold, black square box with vac. line and 3 prong electrical connection) and it's running pretty good. It would also run good with the coolant temp sensor unplugged. I haven't had much time to fool with it, but I've also got charging issues, so I'm hoping that it might go away when I solve those.

If you do figure it out, please let everyone here know. This seems to be happening to several people on here, and no amount of throwing parts seems to fix it.

PS, no mass airflow sensor on TBI motors, so thats a no-go.

cancritter
09-25-2008, 06:19 PM
have a close look at the tbi throtleshaft for any play...if theres play it can throw your tps "throtle position sensor" off..if you havent replaced the TPS would do so as they wear and your trucks got a few years on it and dought prievious owner did...in anycase is one of them things to watch for with tbi's

gr8shot
09-25-2008, 07:41 PM
I'll give it a shot this weekend. Worst case, it doesn't fix it and I take it back and get my money back... I've been reading another thread where the guy replaced his ICM and it fixed a similar problem, but he's burning up ICM's so there's some wiring problems there. It's also worth a shot!!!

SUPERDAD
09-26-2008, 03:55 AM
Verify fuel pressure and base ignition timing. These are 2 things that are not controlled by the PCM. Have found several TBI idle problems that were caused by these being out of spec.

tpulliam79
09-26-2008, 08:53 AM
well my friend owns a shop and he is going to hook it up and check out some readings and such. so I should have some kind of answer later today. I will post the results as soon as I know. thanks for all the advice and im sure ill have more questions. thanks again

bowtiedude
09-26-2008, 09:50 AM
Check your base timing. Check your fuel pressure. Check for throttle shaft play will also create a vacuum leak. Check your vacuum hoses as well.

tpulliam79
09-28-2008, 10:36 AM
well thought we had it narrowed to a dirty injector so I hjad them cleaned and now they flow nicely. hooked a smoke machine up. no vacuum leaks. the timing was advaNCED 3 DEGREES BUT HE TOLD ME THAT WOULDNT HURT ANYTHING... i DONT KNOW MUCH ABOUT TIMING , is 3 ok? and how to check throttle shaft? thanks again

shadowmaker
09-28-2008, 01:07 PM
3* should be ok, I have mine advanced 4*.

EGR, coolant temp sensor, gasket under the throttle body, TPS sensor, intake manifold leak, the computer, MAP sensor.

I think if you have a TBI truck sooner or later you experience some kind of idle problem. At its a headache to figure out. I ve had one for a few yrs. Truck doesnt run bad, just annoying. I go thru spells of replacing stuff trying to find it but the truck is determined for me not to. :dunno: :dunno:

tpulliam79
09-29-2008, 12:10 AM
well I am going to do some more work to the truck tomorrow and I want to seafroam it , is there a way to do it better than the brake booster? I read somewhere that I could pour it right down the tbi? is this true and if so how is it done the most effectively? I have never seafoamed before and want to make sure I am doing it the best way possible. thanks again

tpulliam79
09-29-2008, 09:39 AM
about to put the seafoam in brake booster unless someone tells me putting it in the tbi is better , and how?

NEUMANNZZ
09-29-2008, 09:45 AM
Just slowly pour it into the throttle body, its the best way for tbi. ensure engine is fully warmed up.
did you ohm out the pick up coil and coil.
go here for test:

http://www.autozone.com/az/cds/en_us/0900823d/80/08/5d/3a/0900823d80085d3a/repairInfoPages.htm

tpulliam79
09-29-2008, 10:08 AM
putting a new coil on after the treatment. also pour in tbi while running? and when you say pour in you mean into the same spot the injectors spray in right? sorry I know dumb questions but this is my first tbi experience

gr8shot
09-29-2008, 04:38 PM
any luck?

tpulliam79
09-29-2008, 10:01 PM
well still no luck... new o2 sensor, icm , iac, tps , coil, cap, rotor ,plugs , wires , coolant temperature sensor, fuel filter, had injectors cleaned, mechanic was unsure... going to have fuel pressure tested in a day or two, I need to take a break from this for a day or two, and no vac leaks, and ran seafoam... I am stumped......the short block is from a 78 blazer but the heads are from the 91 shouldnt make a difference though. really seems like a fueling problem at this point hate to say it but I almost hope my fuel pump is the problem as I am out of ideas.

tpulliam79
09-29-2008, 10:33 PM
whats the best way to clean the iac passages ? i need this in laymans terms as my brain is fried. was thinking take out the iac and spray some carb cleaner up there... good or bad idea? thanks also how to remove and clean egr. oh yeah how to test map sensor

tpulliam79
09-30-2008, 09:12 AM
bump

NEUMANNZZ
09-30-2008, 12:36 PM
just spray out the iac/passages with carb spray, engine off.
same with egr cleaning. to test egr. remove vacuum line and plug the line. run engine to see if theres an improvement.
what happens when you disconnect the est bypass wire?

tpulliam79
09-30-2008, 01:30 PM
est bypass wire? is that the timing bypass wire?

aggiedave98
09-30-2008, 02:12 PM
On a '89 burb, I had a problem with the engine dying. I replaced the iac, tps, and maybe something else since disconnecting one of them changed behavior and caused it to run. I was completely stumped. I also replaced the fuel regulator with no luck.

Then somebody told me it could be the fuel pump. Replaced it and bingo! Worked like a charm!

NEUMANNZZ
09-30-2008, 02:43 PM
est bypass wire? is that the timing bypass wire?
yeah

tpulliam79
10-01-2008, 07:27 AM
i will check and clean egr today and see how she runs with the timing wire unplugged today. also noticed I have to give it some gas to start it.( fuel pump maybe?) i will post back after i get the results.

XLR8N
10-01-2008, 07:46 AM
:lol: you shouldn't have to give it gas to start a tbi motor. hmmm. sounds fishy

tpulliam79
10-01-2008, 07:47 AM
:lol: you shouldn't have to give it gas to start a tbi motor. hmmm. sounds fishy

thats what I thought so maybe fuel pump? not sure going to have the pressure tested either today or tomorrow,

oh and where is the fuel pump relay located on my 1991 1500 tbi 5.7. anything besides fuel pump that would cause me to have to give it gas to start?

tpulliam79
10-01-2008, 10:29 AM
would the oil pressure switch have anything to do with idle?

tpulliam79
10-01-2008, 12:06 PM
well it runs worse with timing wire unplugged, there is no vacuum to egr? there is vacuum on the other side of the vacuum solenoid . should there be vacuum at egr while running? and if so would this cause a surging idle?

NEUMANNZZ
10-01-2008, 12:14 PM
I would check fuel pressure(9-13psi) if its running worse with est wire disconnected. that means the egr selenoid is closed. I assume there was no change when you disconnected the vacuum line going to the egr. looks like the egr system is working.

NEUMANNZZ
10-01-2008, 12:16 PM
If the egr selenoid was open then you would have a rough idle and driveability problem.

tpulliam79
10-01-2008, 12:47 PM
going back to my friends shop tomorrow to test fuel pressure and relay. would the relay be the reason why I have to give it gas to start it?

NEUMANNZZ
10-01-2008, 12:50 PM
no.

XLR8N
10-01-2008, 12:50 PM
going back to my friends shop tomorrow to test fuel pressure and relay. would the relay be the reason why I have to give it gas to start it?

i have never heard of a relay "going out" i have always just seen it go out once and it is done. but if you are infornt of your truck looking at your engine bay you will look to the left of the dizzy and on the fire wall you should see a black "shroud" there is three plastic nuts you take off and then take the shroud off and you will see the relay there.

XLR8N
10-01-2008, 12:52 PM
i also dont think a fuel pump going out would make you have to push the gas to start it. unless it isnt pushing enough full through the lines. your injectors are working correctly?

tpulliam79
10-01-2008, 01:06 PM
the injectors seem to be spraying well, if the fuel pressure is right then I guess the next logical step would be new injectors and rebuild of the injector pump and new fpr.. but I will wait and see what my tech says tomorrow. hopefully we can figure it out. oh and my truck will start without me pushing on the gas it just takes about 5-6 seconds of cranking?

XLR8N
10-01-2008, 01:08 PM
so you will push the pedal and crank the engine and it will start right up? and if you do not push the pedal it will take 5-6 cranks?

tpulliam79
10-01-2008, 01:15 PM
so you will push the pedal and crank the engine and it will start right up? and if you do not push the pedal it will take 5-6 cranks?


yeah with gas pushed starts right up without takes some time.

tpulliam79
10-02-2008, 08:06 AM
so you will push the pedal and crank the engine and it will start right up? and if you do not push the pedal it will take 5-6 cranks?


does this point towards something? also the short block is from a 78 blazer and the heads are from the 91 so it would stay tbi, would this cause any differences?
the truck also sounds as if the fans in the dash are always on except when I turn or accelerate but then the sound come right back, no air out of vents but sounds like a small fan in the dash is always going except for when I accelerate or turn?

XLR8N
10-02-2008, 08:32 AM
as far as block and heads different years that is fine it wouldnt be the problem. so did you check your FP?

tpulliam79
10-02-2008, 08:42 AM
gotta take my son to school at 9:40 then im off to my mechanics shop... will post results when I get home. any clue on the noise from the dash?

hornsfan10609
10-02-2008, 08:44 AM
I bet you need a new fuel pump, they go out in almost every truck and usually don't last as long as yours already has. Only go with AC Delco for fuel pumps, unless you want to be replacing it all the time, do it once and do it right.

XLR8N
10-02-2008, 09:03 AM
i have no clue about the fan noise....

tpulliam79
10-02-2008, 12:55 PM
well my mechanic was sick today so I talked to the place where I had the fuel injection cleaning done and he said the pressure from the pump to the injectors was 12 so it checks out .. I will try to go see my mechanic tomorrow and see what he thinks...the other shop told me to try swapping out ecms and see how it runs then they will diagnose after that? I can get one from the yard here for about 70 but seems like a shot in the dark. any opinions?

NEUMANNZZ
10-02-2008, 01:46 PM
For the hard starting.
did they say how long it holds the pressure? hopefully more then a minute. could also be a faulty in tank fuel pump check valve causing the extended cranking.

did you ohm (test) the pick up coil?

tpulliam79
10-02-2008, 01:52 PM
not yet hopefully i will have my tools back tomorrow.

tpulliam79
10-03-2008, 09:18 AM
well its going to a shop somewhere today, but i noticed the gauge inside never gets above 160 degrees, i am going to put a heat gun on it to see if thats as hot as it is really getting if it is only getting to 160 would that cause it to idle strange looking for closed loop?

tpulliam79
10-03-2008, 08:52 PM
bump

XLR8N
10-04-2008, 06:32 AM
If it is 160* than you need to replace your thermostat with a
185*

tpulliam79
10-04-2008, 09:42 AM
If it is 160* than you need to replace your thermostat with a
185*
would this cause a weird idle?

XLR8N
10-04-2008, 09:55 AM
well, i would rather run 185* thermostat in a stock truck. And you are in WA also so it isnt like living in texas. I would not think that would cause your idle probs though.

tpulliam79
10-04-2008, 04:44 PM
well finally got in to the mechanic fuel pressure is good, he says its an intake manifold gasket leak ,confirmed with some carb spray, can actually see where it got sucked in, the guy who rebuilt this must have installed them wrong... at least I know whats wrong now, hes going to replace them and put the tbi tune up kit on next week for me for $150 and said if that doesnt fix it hell be working on it for free until its fixed.... so hopefully this will do it I will post next thursday evening with results.. I know there are a few others having alike issues so hopefully this may help them too

also noticed the knock sensor wiring connector was broken and hanging down so I fixed that also

XLR8N
10-06-2008, 06:32 AM
cool, good price.

tpulliam79
10-06-2008, 12:53 PM
going to replace thermostat ans temp switch and put tune up kit on throttle body and injector pump. Is there anything else I should do while its apart?

XLR8N
10-06-2008, 01:26 PM
I would replace the water pump too if it was me. 30 bucks for a brand new one and im sure the mechanic wouldnt charge you much more if not anything. maybe the pcv valve too. clean it up real good and you'll be set.

tpulliam79
10-09-2008, 07:05 PM
well the intake gasket was replaced and it needed it and the tbi all tuned up ran great until we reved the engine then back to a surging idle not as bad but still there. he only charged me 1/2 of the labor and is going to do some more diagnosis this weekend. Boy I do love my truck but ive put almost 1000 into it in the first two weeks, any ideas?

rich_e_rich73
10-09-2008, 07:13 PM
just a thougt try unpluging the lockup tork converter it may be draging or not unlocking completly

nickmac
10-09-2008, 08:08 PM
Where did you get the CTS? I went through 2 of them from Autozone in 2 months, I fixed the problem with one from the dealer. The CTS can be checked with an ohmmeter. Did you clean the EGR valve yet?

tpulliam79
10-09-2008, 10:14 PM
the egr passages in the intake were completely clogged but clean now. coolant temp sensor is new from autozone . how does the ohm test work?

gr8shot
10-09-2008, 10:42 PM
just looked at my haynes manual for the coolant temp sensor ohm test. with the engine cold, test resistance across the terminals (wire harness disconnected, one test probe on each of the connections) readings should be anywhere from 2200ish at ~85* to 5600 at ~55*F. Warm the truck up, and repeat the test. Readings shoud be in the hundreds of ohms. Like below 500 or 600. The sensor is made to vary resistance with temperature, so the warmer the engine gets, the less resistance there is in the sensor.

tpulliam79
10-09-2008, 10:57 PM
thanks. also I was comparing some parts to see what all vehicles I can get a ecm out of, does it have to be same year and all or just the same part number off the ecm?

bfmh16
10-18-2008, 12:01 AM
Try replacing the broken spring inside the fuel pressure regulator.

tpulliam79
10-18-2008, 03:05 PM
spring wasnt broke its all been redone, switched ecu took care of most of the issue now my 02 isnt reading very well, but i also had a bad thermostat in there so it wasnt going closed loop, thats being fixed the tranny shift points being adjusted and a bunch of new grounds. does the o2 have a ground? also hydrocarbons are very high and I have a fairly new cat?

NEUMANNZZ
10-18-2008, 03:50 PM
The o2 sensor is grounded in the ecm if its a two wire.(tan wire)

tpulliam79
10-18-2008, 03:53 PM
the truck isnt here but I think only one wire

tpulliam79
10-20-2008, 05:41 PM
if they didnt change the cam out of the 78's short block and put the 91's heads on for the tbi , would that affect anything? vacuum or otherwise? I also had the wrong prom in the new ecm so ill know shortly about the ecm

tpulliam79
10-21-2008, 08:53 AM
i am not sure if the cam is from the 78 or the 91 would it cause any issues either way?
also would the return line on the tbi unit being kinked cause any idle or richness issues?

tpulliam79
10-21-2008, 12:29 PM
well what I am being told is that the cam out of the 78 blazer was used and my mechanic is saying that at idle my vacuum is 14 lbs and it should be 18 and the cam is causing it ...or something in the shortblock. is there anything else this could be the shortblock is out of a 78 with 32000 original miles and runs super strong when not at idle, I really dont want to replace the engine as I am not rich by any means. can I custom tune or anything other than tearing the engine apart? any and all help is appreciated beyond what words can say

just talked to a chevy tech and was told the cam being from the 78 shouldnt affect anything.... now im really stumped

tpulliam79
10-21-2008, 05:15 PM
well my mechanic brought my truck to the house and as he pulled in the radiator drain**** burst ( which he just put in) but says its nothing he did? anyways now im replacing the radiator and realizing I dont think I trust my mechanic anymore. he says the vacuum pressure at idle is 14 and should be 18 and says that the cause is the 78 small block"s cam being different. Chevy says that wouldn't affect it? also that it dumps fuel at idle because the vacuum pressure is off. he never did check the fuel pressure.. wow sorry to rant but I am freshout of ideas and needed to clear the head....does any of this make sense to anyone?....thanks again

sorry about the rant..... does 14 sound right for vacuum at idle? and if the cam is in some way messing with vacuum and causing too much fuel at idle could a custom tune do anything for me?

tpulliam79
10-21-2008, 10:50 PM
ttt

NEUMANNZZ
10-22-2008, 08:52 AM
14 is low for vacuum, any leaks. valves adjusted correctly. A stock 350 cam shouldnt cause that much of an issue unless its worn out. compression and leakdown test results?

tpulliam79
10-22-2008, 09:11 AM
not sure of the compression and I was told by my mechanic that the vales arent adjustable
( I dont believe him) how would I go about compression and leak down testing myself? my EX-mechanic even told me that my truck has more power than a stock 91 tbi because of the cam differance but says thats why the vacuum is off the short block and cam have just over 30000 miles on them so they shouldnt be worn out.
I am putting in a new radiator today and was thinking of replacing the distributor as the top under the rotor is very rusty and seems to have a good amount of play, is thhis normal?
I can fix just about anything once I know whats wrong but am a complete newb when it comes to diagnosis and testing. also if I do put a new distributor in how do I go about getting it lined up right, I have no timing light but I know its timed now?

nickmac
10-22-2008, 08:11 PM
On your 91 there is a wire to disconnect to set the timing. It should be behind the plastic on the passenger side of the firewall. The return line being kinked could be letting it run rich because not enough fuel is getting back to the tank.

tpulliam79
10-22-2008, 10:23 PM
yeah I know about the wire but I have no timing light and wouldnt know how to use it anyways, it is only dumping fuel at idle think the kink would cause that?

also if I get a new dizzy should I get the one for the 91 heads or the 78 shortblock? the camshaft is from the 78 would the wrong dizzy cause issues?

NEUMANNZZ
10-23-2008, 08:39 AM
78 had hydraulic lifters. my 66 had hydraulic lifters. you can adjust the valves. distributor drive gear should be the same. get the 91 tbi distributor,
unless your gonna switch to carb then get a HEI with vacuum advance.

tpulliam79
10-23-2008, 08:43 AM
looks like I need a new mechanic.... as soon as I can afford it im going to have it emissions tested then take it to chevy that way the work I have done will at least count towards a waiver. would the top of the dizzy being rusty and having play cause issues like this?

NEUMANNZZ
10-23-2008, 09:05 AM
yeah if the play is more then a 1/4 of an inch. rust is normal as long as its surface rust.

tpulliam79
10-23-2008, 09:10 AM
ok so if I get a new dizzy how do I go about getting it in correctly as I have no timing light?

NEUMANNZZ
10-23-2008, 09:36 AM
invest in a new/used timing light.
to install distributor, before removing old distributor mark position of rotor and housing.(dont mark the old distributor)

rotor positon can be turned by cranking engine to get it number one cylinder on distributor cap for easier reference, then just mark the housing location. photos help also.

once you marked the two positions. remove hold down bolt on clamp. pull out distributor slowly. rotor will turn while pulling it out, keep this in mind when installing new distributor to line up rotor location.

NEUMANNZZ
10-23-2008, 09:48 AM
A timing light is good for checking to see if timing is advancing. setting timing. checking timing to see if the ecm retards timing due to knock. checking for erratic timing(internal mechanical issues, ie timing chain loose)

tpulliam79
10-23-2008, 10:22 AM
well put a stethoscope on the dizzy and it sure doesnt sound right seems like it makes a weird sound right before the idle gets funny.. how do you use a timing light?

FordeatinZ71
10-23-2008, 11:46 AM
ok, maybe i've missed this...how are you running a '78 cam in a '91 block? the '91 is a roller cam...the '78 is not...again, maybe i missed it as i just skimmed this.

are you sure it's firing on all 8? might wanna do a compression test. have you replaced the coil or ignition module yet? those can both cause weak spark and the ignition module can cause the injectors not to work right.

NEUMANNZZ
10-23-2008, 12:37 PM
ok, maybe i've missed this...how are you running a '78 cam in a '91 block? the '91 is a roller cam...the '78 is not...again, maybe i missed it as i just skimmed this.

are you sure it's firing on all 8? might wanna do a compression test. have you replaced the coil or ignition module yet? those can both cause weak spark and the ignition module can cause the injectors not to work right.
91 is not a roller cam.

NEUMANNZZ
10-23-2008, 12:44 PM
well put a stethoscope on the dizzy and it sure doesnt sound right seems like it makes a weird sound right before the idle gets funny.. how do you use a timing light?

its easy hook it up to the battery(red wire to red +/ black wire to black - battery terminals). then hook the induction pickup to # 1 spark plug wire(be careful not to burn it on exhaust). start engine point timing light to balancer and timing tab. pull trigger and enjoy the light show(light will flash). balancer mark will line up with timing tab zero degrees. if not rotate distributor slowly until it lines up(loosen holdown bolt until its just snug)

tpulliam79
10-23-2008, 01:13 PM
the block is from a 78 the heads are from the 91 cam is from the 78

thanks for the heads up on the timing procedure. once I get a light i will check it out

dunnroadmafia
10-23-2008, 01:44 PM
i am having this exact problem with my 93 tbi 350 and my mechanic, dad, uncle and damn near every one i know thinks its the distributor. So please keep us posted and good luck

tpulliam79
10-23-2008, 01:50 PM
well my mother has fallen on some bad times so all my extra money is going to her for now, but as soon as I get through this and my six year anniversary I will be working on it again. I will post as soon as I know something or run into more questions

FordeatinZ71
10-23-2008, 04:13 PM
91 is not a roller cam.

well i'll be damned! i always thought 87-up motors were roller cammed...learn something new every day, thanks man!

tpulliam79
10-25-2008, 04:04 PM
dumb question... the power steering doesnt affect vacuum does it? seems like the idle gets way off anytime im stopped and turn the wheels?

tpulliam79
10-26-2008, 02:18 AM
bump

frank1
10-26-2008, 08:13 AM
check your egr valve for carbon build up. the egr valve should be closed at idle. the carbon will not let it seat all the way closed and it won't set a code. Just had the same problem with my 2000 k2500 5.7. good luck. Frank

NEUMANNZZ
10-26-2008, 08:56 AM
dumb question... the power steering doesnt affect vacuum does it? seems like the idle gets way off anytime im stopped and turn the wheels?

No, but it will put a load on the engine.

tpulliam79
10-29-2008, 07:39 AM
so i have my anniversary coming up and my wife is going to buy me whatever I want and it looks like its going to be parts..... when we did the intake gasket the egr passages were completely clogged with carbon, obviously we cleaned them out think its safe to assume that there is a lot of carbon build up in the egr iself? also would the egr cause low vaccuum at idle? and if I recall correctly when my mechanic was checking timing I dont think it changed after the est wire was reconnected, what would cause that? the knock sensor wasnt hooked up for some time, is there a way to check this? here are all the new parts already in.... themostat, o2, plugs , wires, cap, rotor, icm , coil, cts,intake gaskets, tbi all new gaskets and cleaned, tps , map, and iac ,

heres what I was thinking of getting ( still fighting a rough idle and now it seems to miss when cold)
distributor, knock sensor, egr valve, egr solenoid, oil pressure sensor, and a timing light

think im chasing my tail here?

NEUMANNZZ
10-29-2008, 11:14 AM
your egr could affect vacuum if the diaphram is ruptured/sticking or the EGR selenoid is stuck open.

timing should advance with the est wire plugged in and code 42 reset. at idle it should be around 20 degrees. when you give it gas it should advance further.

the ECM controls spark advance with the est system. to properly control ignition the ecm needs to know
cranshaft position
engine speed
engine load(manifold vacuum)
atmospheric pressure
engine coolant temperature.

tbi distributor 101:
the four post connector to the distributor:
pin A: reference ground low, may be ground to distributor, it makes sure the ground circuit between ecm and module. if open may cause poor performance.

pin B: bypass. at about 400 rpms the ecm applies 5 volts dc to this circuit to switch spark timing control from the module to ecm. an open or grounded bypass circuit will set code 42 and the engine will run at base timing, plus a small amount of advance built into the module.

pin C: distributor reference high. this provides the ecm with rpm and crankshaft position info.

pin D: EST. this circuit triggers the module. The ecm does not know what the actual timing is but it does know when it gets the reference signal. it then advances or retards the spark from that point. therefore if base timing is set incorrectly the engine spark curve will be incorrect.

results of incorrect est operation:

low map output voltage: more spark advance
cold engine: more spark advance
hot engine :less spark advance
high map output voltage: less spark advance

detonation can be caused by high map output or high resistance in the coolant temp sensor circuit.

poor performance can be caused by high map output or low resistance in the coolant temp sensor circuit.

DIAGRAMS HERE:

http://www.fullsizechevy.com/forums/attachment.php?attachmentid=10893&d=1206741675

http://www.fullsizechevy.com/forums/attachment.php?attachmentid=11294&d=1220576357

PICKUP COIL AND COIL TEST:

http://www.autozone.com/az/cds/en_us/0900823d/80/08/5d/3a/0900823d80085d3a/repairInfoPages.htm

tpulliam79
10-29-2008, 11:50 AM
ok just got back from Meineke for some warranty work, they are telling me the cat is bad and this is why im having issues. another shop tells me that the cat and muffler cant affect anything at idle? im confused. also whoever had truck before me welded in a 2 inch muffler and all the other pipes are 3 inch obviously causing restriction. the muffler is going to be replaced in the next couple days, had the cat backflow tested and they said its 1 lob and is not plugged. could the cat being bad ( not working right) and the wrong size muffler affect anything at idle?

NEUMANNZZ
10-29-2008, 12:08 PM
If the cat is plugged up(excessive backpressure) yes you can have problems, but usually not at idle, usually under load. a 2 inch in/out muffler shouldnt cause an issue unless its plugged up too.

NEUMANNZZ
10-29-2008, 12:09 PM
just becuase they said the cat is bad probably means you wont pass emmissions.

tpulliam79
10-29-2008, 12:38 PM
so the cat and muffler are not affecting the idle then you think

NEUMANNZZ
10-29-2008, 02:41 PM
probably not.

tpulliam79
10-29-2008, 06:51 PM
well its got to be fixed either way so im gonna get the exhaust all redone with single in and dual out new pipes and tips.. the shop owner says hes 99% sure that this wiull fix my problem I told him if it doesnt then he has to diagnose it for free...

C/K1500
10-29-2008, 06:53 PM
1. There is nothing wrong with your cat. The motor has no idea if there even is one, since it is mounted behind the O2 sensor. If it is plugged, you will lose pwer on the highway. At idle there would be no issue.

2. You have not mentioned if your injectors are spraying nicely or dribbling fuel. If they are dribbling, that could be your problem.

3. You could have an air leak at the throttle shaft. Grab it and see if there is play. If there is, see if the play is the same at different throttle openings. Most wear occurs (and the most impact to drivability) at the throttle tip-in point.

4. Make sure you ignition wires, etc. are good. SOmeone pasted an Autozone link and that shows you good ways to rule out an ignition problem.

5. Your vacuum is too low at idle. 1978 Chevys idled at 21 inches of mercury. There is no problem with your cam (unless of course it has flat lobes). Since you have no problems at higher rpm or under load, I would rule out the cam as a problem. You might still have a vacuum leak due to improperly installed manifold gaskets or a warped manifold. Since you feel that the mechanic who reinstalled the manifold gaskets was a gibroni, perhaps he did not do this job well.

6. A bad EGR valve will cause drivability problems, such as excessive pinging at speed. I have seen brand new, faulty EGR valves right out of the box. These engines need exhaust recirculation to run well.

7. A bad knock sensor will cause - your engine to knock (ping) like crazy. You have not reported that as a problem, so look elsewhere.

8. You should have a 195 degree thermostat. That is what your ECU is calibrated for. The warmer the better for driveability and economy. For drag strip performance, yes, go cooler. But not on a street car or with today's gas prices.

9. To set the timing with a timing light, you must disconnect that wire as described in a previous posting. Set the timing as far ahead as you like. It doesn't matter that much, as long as the engine does not ping once you reconnect everything and drive it. You will notice that retarding the timing tends to give a smoother idle, but the engine will have no balls. Advancing slightly, the engine idles with a bit of a 'roll' or occasional hiccup, but has more power. In general, run the most timing for the grade of gasoline that you use that does not cause the engine to ping under the type of driving you normally do.

10. A bad MAP sensor could cause problems. Did you already change yours? I believe that you did. But a MAP sensor is not the first place I would be looking as they tend to fazool things farther up the power band.

Lastly, remember the first law of auto repair shops: the problem you have can only be fixed by whatever high-margin parts that shop sells. So, if you take the truck to Meineke, it will need a new cat for whatever problem you showed up with. As so on and so forth.

Good luck, and let us know.

C/K1500
10-29-2008, 06:58 PM
1. There is nothing wrong with your cat. The motor has no idea if there even is one, since it is mounted behind the O2 sensor. If it is plugged, you will lose pwer on the highway. At idle there would be no issue.

2. You have not mentioned if your injectors are spraying nicely or dribbling fuel. If they are dribbling, that could be your problem.

3. You could have an air leak at the throttle shaft. Grab it and see if there is play. If there is, see if the play is the same at different throttle openings. Most wear occurs (and the most impact to drivability) at the throttle tip-in point.

4. Make sure you ignition wires, etc. are good. SOmeone pasted an Autozone link and that shows you good ways to rule out an ignition problem.

5. Your vacuum is too low at idle. 1978 Chevys idled at 21 inches of mercury. There is no problem with your cam (unless of course it has flat lobes). Since you have no problems at higher rpm or under load, I would rule out the cam as a problem. You might still have a vacuum leak due to improperly installed manifold gaskets or a warped manifold. Since you feel that the mechanic who reinstalled the manifold gaskets was a gibroni, perhaps he did not do this job well.

6. A bad EGR valve will cause drivability problems, such as excessive pinging at speed. I have seen brand new, faulty EGR valves right out of the box. These engines need exhaust recirculation to run well.

7. A bad knock sensor will cause - your engine to knock (ping) like crazy. You have not reported that as a problem, so look elsewhere.

8. You should have a 195 degree thermostat. That is what your ECU is calibrated for. The warmer the better for driveability and economy. For drag strip performance, yes, go cooler. But not on a street car or with today's gas prices.

9. To set the timing with a timing light, you must disconnect that wire as described in a previous posting. Set the timing as far ahead as you like. It doesn't matter that much, as long as the engine does not ping once you reconnect everything and drive it. You will notice that retarding the timing tends to give a smoother idle, but the engine will have no balls. Advancing slightly, the engine idles with a bit of a 'roll' or occasional hiccup, but has more power. In general, run the most timing for the grade of gasoline that you use that does not cause the engine to ping under the type of driving you normally do.

10. A bad MAP sensor could cause problems. Did you already change yours? I believe that you did. But a MAP sensor is not the first place I would be looking as they tend to fazool things farther up the power band.

Lastly, remember the first law of auto repair shops: the problem you have can only be fixed by whatever high-margin parts that shop sells. So, if you take the truck to Meineke, it will need a new cat for whatever problem you showed up with. As so on and so forth.

Good luck, and let us know.

tpulliam79
10-29-2008, 09:13 PM
well I am going to check everything I can again friday and from there figure out if the truck is going to the muffler shop , or if im going out and buying more parts, both need to be done just which one now which one in two weeks... working on a very structured budget, especially with all that is coming up.
I have to drive the truck about 300 miles tomorrow so I will see how it goes and then decide...

tech129
10-29-2008, 09:23 PM
do you know if your running the stock cam for this truck ? im using an rv cam 204/214 in my 94 ecsb 4x4 and my blm is at 95 and my idle surge after a few secs let me know tech 129

bowtiejack
10-29-2008, 09:51 PM
couldn't read thru all these posts but the cam guy was on the right page. sounds like the computer can't keep up with the readings for fuel management, pardon me if you covered this but after timimg check and fuel pressure constant( once it was the fuel filter) i normally go from tps to the ecm inside the distributor . back to the cam dude. if you made performance upgrades like a cam,heads,etc. it might need a new chip-mines from fastchip.com but there are better/more expensive chips out there. anyways, if i was a help-great, if not and somebody already covered this -sorry.

tpulliam79
10-30-2008, 06:53 AM
couldn't read thru all these posts but the cam guy was on the right page. sounds like the computer can't keep up with the readings for fuel management, pardon me if you covered this but after timimg check and fuel pressure constant( once it was the fuel filter) i normally go from tps to the ecm inside the distributor . back to the cam dude. if you made performance upgrades like a cam,heads,etc. it might need a new chip-mines from fastchip.com but there are better/more expensive chips out there. anyways, if i was a help-great, if not and somebody already covered this -sorry.


so are you saying you also think the cam could be suspect? the small block and cam have just over 30000 miles on them

tpulliam79
10-30-2008, 04:38 PM
bump

tpulliam79
10-31-2008, 07:49 AM
well the truck drove great on the 350 mile trip , got 17 mpg, ran very smooth while running except that it felt kinda doggish at higher power, also the cruise control kicked off and wouldn't come back on, and anytime i gave it more than 3/4 throttle it would stick and i would have to nail the gas pedal a few times until it would let off? once i get my little one off to school I'm going to check some things, I was thinking fuse for cruise control and throttle cable for the sticking acceleration....any other ideas?

bowtiejack
11-01-2008, 08:44 PM
if it was the cam , it would have idled erratic it from the start. the computer chip can only read so fast and make adjustments to the fuel delivery. you can put a dramatic cam inside that would run like greased lightning but wouldn't idle fer sh*t .so if the engine idled fine when the cam/heads went on , that ain't it.when you get a chance. get the engine up to temperature. take some carb cleaner and spray some down the two sides,front and rear , of the intake where it mates to the engine deck. any stumple or rise in rpms would be a gasket leak. use the same method around vacuum lines and its connections. don't get liberal, just enough to check for leaks. let me know what happens and we'll go from there.i'll try to check back regularly to see how its going .

kevinschoeneman
11-02-2008, 07:13 PM
Try pluging the vac line to the EGR after the moduel, it worked for me , tho couldn,t tell you why

bowtiejack
11-04-2008, 05:30 PM
the egr , behind the tbi on the passenger side , has a baffle on the underside should flex in and out helping to modulate the idle. if it sticks or doesn't suck in and out, it will cause a rough idle but i believe it will flash the check engine lite as it is part of the emissions . to replace it, get the long model number off the original because there are alot of different versions thru out model years.

tpulliam79
11-20-2008, 10:36 AM
well havent had time or money for awhile but now i may start trying again.. now at cold startup the engine cuts out or misses real bad goes away after it warms up but then the idle is still eratic at idle? almost feels like a timing issue but i dont know any suggestions?

NEUMANNZZ
11-20-2008, 11:00 AM
did you ever check the timing?

tpulliam79
11-20-2008, 12:43 PM
its been absolutely nuts here but hopefully tomorrow i can go get a timing gun and check it out, but the last time it was at a mechanic they checked it and said it was fine but I dont recall it jumping around after we hooked the est wire back up

NEUMANNZZ
11-20-2008, 12:56 PM
definitely check timing and if it advances with est plugged in.
with the est wire disconnected timing should not be erratic.

also if the engine runs good with the est wire disconnected check the pick up coil. test here:

http://www.autozone.com/az/cds/en_us/0900823d/80/08/5d/3a/0900823d80085d3a/repairInfoPages.htm

tpulliam79
11-26-2008, 12:01 AM
well ended up taking it to a different mechanic and they found that the intake was still leaking, so much to my distress I had to call the other shop where I just paid to have the intake done, he agrees to fix it again but still says its the block or possibly a bad intake , the other shop gave me a free known good intake off one of the techs trucks so that way if this guy wants to say its the intake I have another there already...what does the block have to do with the intake gasket doesnt the intake bolt to the heads not the block? is there anything that could be mistaken for an intake leak?
the leak is at the passenger side rear corner

NEUMANNZZ
11-26-2008, 11:00 AM
maybe they want to sell you a new engine. :eek:

tpulliam79
11-26-2008, 01:15 PM
thats what the mechanic im taking it to says but i what does the shortblock have to do with the intake gaskets? even if something was wrong with the shortblock how does that affect the intake leaking?

NEUMANNZZ
11-26-2008, 01:29 PM
unless they did a compression test, it wouldnt effect the intake to block. if they didnt put a big enough bead of rtv then you would just have oil leaking.

tpulliam79
11-26-2008, 03:09 PM
he says he will only fix it once because its the wrong short block but shouldn't they be able to fix the intake either way

tpulliam79
11-27-2008, 10:52 PM
is there any reason the intake wouldnt seal because of the different shortblock?

tpulliam79
11-28-2008, 09:05 AM
gotta take the truck to the shop in a bit . is there any reason the shortblock from the 78 with the 91 heads would cause the intake not to seal?

NEUMANNZZ
11-28-2008, 12:02 PM
No.

tpulliam79
12-05-2008, 11:41 PM
well the mechanic has still not fit me in and he says he thinks its the intake because " he's done 1000's of these intake gaskets and never had one leak" says hell pull the intake and see if the gasket is baad or in wrong and if it is hell put the new one on no charge but if its not I have to pay him labor to put the other intake on...... and due to some absolute craziness money is more than tight. question is this how hard would this be to do myself with one good arm and a friend? I did the intake gaskets on my supercharged bonneville..... doesnt seem to be that much but im not 100% on this one... I have factory service manuals for the bonneville but not the truck yet.

NEUMANNZZ
12-06-2008, 11:07 AM
probably easier to do on the truck. more room.

tpulliam79
12-06-2008, 11:09 AM
any body have a link to the step by step guide so as Im sure im pulling the right stuff?

NEUMANNZZ
12-06-2008, 11:19 AM
not a very good guide:

http://www.autozone.com/az/cds/en_us/0900823d/80/08/5d/a7/0900823d80085da7/repairInfoPages.htm

Bandit1188
12-10-2008, 09:34 AM
bump

bowtiejack
12-16-2008, 07:20 PM
before you go just switching intakes , get it up to temperature and spray some carb cleaner along the rails( where intake mates to the heads)and see if the idle stumbles and increases . to replace the intake- three-five hour job . buy a chiltons book . three points. get a decent torque wrench and do a 2 step torque in the right sequence. make sure the intake side rails have the block out plate at the passenger side rear . lastly use a heavy bead of black rtv at the ends instead of the paPER gaskets . and hey, do a real good oil drain and fill after cause when you first lift the intake water will mix with the oil .

tpulliam79
12-20-2008, 11:10 AM
well my "mechanic" re - installed different gaskets and the other intake, and says its still doing it( idles jumping ) .. he is saying its something to do with the short block thats making the intake not seal correctly. If they machined the block from the 78 blazer when matching it with the 91 tbi heads and they did something wrong is there any way that would cause the intake not to seal or it to appear to have a leak in the intake right back at the passenger side rear corner under the egr area? he says I have to sign something saying he doesnt have to fix it again and now he wants 100 ? trying to find out if I need a new or different short block or a different mechanic.. when not at idle it runs great

NEUMANNZZ
12-20-2008, 11:14 AM
if the gap is too wide because someone machined to much off the block or incorrectly machine the head intake surface differently.
Makes sense to me. maybe its time to save up and get a different engine.

Jasper911
12-21-2008, 09:18 AM
Yuck, feel the pain.

I'm glad I'm not the only one dumping tons of money into an old truck. Mines doing similar stuff. Replaced the 305 with a 355 roller with Comp cams computer cam/flat tops/roller rockers etc. The 305 seemed worn out and ran rich, but still having same problems with new engine.

Might want to check the vehicle speed sensor. Mine was pretty jacked up looking and surely no good, but still not my problem.

Interested to see if there's any closure on this one.

I wouldn't go looking for a new engine just yet.

Jasper911
12-21-2008, 04:03 PM
Oh,

Just realized a pattern tonight. When I've got a full or mostly full tank, the truck runs great. Just filled up with 14 gallons a while ago. Was running like a dog before I did. It seemed like the truck would run great for a few days then go down hill and back to its old ways. I never kept a lot of gas in it until I started breaking in the new engine. I also have an erratic tank sender...which usually doesn't work. I think I'm gonna go ahead and replace the sender and the pump while I'm in there.

Rabbitiswise70
12-21-2008, 07:08 PM
Oh,

Just realized a pattern tonight. When I've got a full or mostly full tank, the truck runs great. Just filled up with 14 gallons a while ago. Was running like a dog before I did. It seemed like the truck would run great for a few days then go down hill and back to its old ways. I never kept a lot of gas in it until I started breaking in the new engine. I also have an erratic tank sender...which usually doesn't work. I think I'm gonna go ahead and replace the sender and the pump while I'm in there.


Try a new gas cap. Some trucks like a little more pressure in the tank. If its an orginal cap,,it could be releaving too much.

Just a thought. Let me know if that works for you.

tpulliam79
12-21-2008, 10:17 PM
my gas tank has nothing to do with it the engine isn't missing when cold anymore just surging at idle. It runs great except at idle, I have to get it through emissions in the next couple weeks, if nothing else ill get a waiver for it and go from there. I really like the truck and think ill just drive it until i can afford to put a new engine in it. think i may be trading my supercharged bonneville for a 96 tahoe ( once my mechanic checks it out).

Jasper911
12-22-2008, 02:51 PM
my gas tank has nothing to do with it the engine isn't missing when cold anymore just surging at idle. It runs great except at idle, I have to get it through emissions in the next couple weeks, if nothing else ill get a waiver for it and go from there. I really like the truck and think ill just drive it until i can afford to put a new engine in it. think i may be trading my supercharged bonneville for a 96 tahoe ( once my mechanic checks it out).

I wouldn't be so quick. This sort of thing just set me back about four grand!!!!

Rabbitiswise70
12-25-2008, 05:54 PM
Does the Truck still have the charcol canister still hook up? If yes, check the lines for breaks. It could be causing a vac leak.

tpulliam79
01-05-2009, 02:45 AM
checked lines no leak... new intake and gaskets and now it seems to only do it in park and reverse? I love my truck but am real close to trading her in ....gotts get through emissions and at this point its not gonna happen . Not to mention the 70 inches of snow we have gotten in the last 3 weeks.

FordeatinZ71
01-05-2009, 12:02 PM
if you really love it and don't wanna trade it, then just give it to a shop to fix. you are wasting time troubleguessing and wasting money too...if you can't figure it out (we've all been there) then just let a decent shop do it for ya. i have a friend in Seattle who might be willing to lend a hand...if i can get ahold of him...

tpulliam79
01-05-2009, 01:50 PM
its been to three shops 2 said intake leak at rear passenger corner I have had the gaskets done twice and put a new intake manifold on also the other shop saya its cat and muffler, but cat and muffler wouldnt be noticable only at idle

cancritter
01-05-2009, 02:35 PM
l feel for ya...have you had it in to a GM dealer yet?
like yourself l dont mind payin the extra buck to have it done right the first time and if theres a prob the balls to stand behind thier work and tell ya straight up what prob is....
l realy dont know what to say..could be half a dozen things and for most here is like a doc doing a diagnosis over the phone...personaly ld take it to a reputable gm dealer and let them have a boo at it...at least youll have some sorta warentee in the end or a good idea whats wrong...
at this point have fergoten if you have internal engine mods to deal with as well...if so you gotta drag the whole thing to a dyno/mech shop or your just grabbin at straws trying to get it set up

Rabbitiswise70
01-12-2009, 08:44 PM
checked lines no leak... new intake and gaskets and now it seems to only do it in park and reverse? I love my truck but am real close to trading her in ....gotts get through emissions and at this point its not gonna happen . Not to mention the 70 inches of snow we have gotten in the last 3 weeks.


Do you know some that can hook a scanner(not a code reader) to look at data, and possible pull the soft codes(codes that do not trip check engine light on) if there are any?

The other question would be, has the O2 Sensor been replaced? That sometimes can cause it. Thats were a scanner would come in handy, you could see if the O2 is switching or not. Also you could see if the IAC is working properly. In fact trying tapping the IAC when in park and see if the idle changes.

tpulliam79
01-12-2009, 10:24 PM
new iac and o2

Jasper911
01-24-2009, 07:16 PM
I think I solved my problems today. I bought a used ecm from pull a part. It was actually out of an Astro but had the same service #. It runs much better so far and just for the heck of it, I've been playing with the e-proms from the 4.3, 5.0, and one from a Suburban that was either a 5.7 or a 7.4. The one from the Suburban just raised the idle and offered nothing performance-wise. However the 4.3 prom seemed to significantly improve power but smells a bit too rich. I'll drive it for a few days and see.

tpulliam79
01-25-2009, 08:29 AM
yeah I tried new computer still no luck but after the work i have been doing on my 88 something occurred to me, the return line on my 91 from the throttle body is kinked pretty good, looks like someone tried to remove the fittings and bent it pretty good, now im wondering if the restriction in the line could be causing too much gas built up and may be causing my up and down idle? what do you guys think?

NEUMANNZZ
01-25-2009, 09:03 AM
I would fix the kink.

smblksrock
01-25-2009, 09:07 AM
CHECK THE EGR VALVE! At least take it off and clean all the carbon off. Alot of idle issues are egr's leaking or stuck open. This should be your FIRST suspect along with dirty IAC, then go from there.

tpulliam79
01-25-2009, 09:08 AM
is there a gasket under the egr valve? think the kink could cause these issues? i am heading to the yard tues to grab a new return line.

kavemanlee
02-01-2009, 08:50 AM
I have the same truck with the same symptom if yours is an automatic also. A local mechanic isolated it down to the probability of the gear selector sending mixed signals,ie; "I'm in Drive, now I'm in Nuetral, now I'm in Drive". I haven't tried to fix it yet but my idle remains mostly stable at 550 rpm if the traffic light isn't too long.

tpulliam79
02-01-2009, 09:42 AM
sounds just like mine, and i have to hold the gear selector to the left if I want my reverse lights to come on. how is this fixed? I dont know that that is the issue with the idle but maybe I will kill two birds with one stone. If anyone knows how to adjust this please let me know ...thanks

cancritter
02-01-2009, 09:53 AM
theres a adjustment at the steering colum in engine bay..losen nut and adjust accordingly...not shure this is what your after,,

as for kink in return line ..yes fix asp...if its bottlenecking return gas then it in turn is acting like a fuel regualtor and may be starveing engine

tpulliam79
02-01-2009, 09:57 AM
the adjustment of the nut on the column in the bay will adjust the prindle ( for lack of proper term) and make the gear selector adjustment? I just want my reverse lights to come on when in reverse so people and cars will stop coming behind me as I reverse. and I am going to the yard tomorrow to get another return line.

Jasper911
02-23-2009, 07:28 PM
My problem isn't solved either. I have tried three different egrs, one new, one from old engine and one from new engine before rebuild. All the same.

Still runs very rich. even blows a blueish smoke at times under load just off idle, but not oil smoke. This is unburnt fuel. The throttle body is the only thing I have never changed out and it has 255K. Possible worn throttle shaft giving false TPS info?

It will idle up briefly after letting up from giving it throttle. Also notice an oscillation up and down while parked in gear idling. At times under acceleration (from a stop) it hesitates then when I let off it responds. Like it's doing the opposite of my command. Annoying and seems hard on the trans and drive line.

Jasper911
03-02-2009, 06:37 PM
Man

I kinda feel like a dunce. My vapor canister was leaking around the top. We checked it a while back, but not very well. I blew into the hose and felt the leaks. For now I just plugged the fitting on the throttle body. It's running excellent...duh!

cancritter
03-02-2009, 06:42 PM
yeah I tried new computer still no luck but after the work i have been doing on my 88 something occurred to me, the return line on my 91 from the throttle body is kinked pretty good, looks like someone tried to remove the fittings and bent it pretty good, now im wondering if the restriction in the line could be causing too much gas built up and may be causing my up and down idle? what do you guys think?


as a general rule when you put in a aftermarket fuel regulator you put it in the return line....
the kink could be possible acting like a fuel regulator and starveing your engine...fix line and keep fuel lines as far away from exhaust or they will get hot and perculate giveing you same symptoms as a pluged or restricted fuel filter

cancritter
03-02-2009, 06:50 PM
My problem isn't solved either. The throttle body is the only thing I have never changed out and it has 255K. Possible worn throttle shaft giving false TPS info?

.


bang on with the throtle body shaft...gotta watch that on older tbis..even small amount of play is enough to throw things outa whack...for future refrence

Jasper911
03-02-2009, 07:11 PM
I could never move the throttle shaft up and down enough to cause any idle change. It did have a bit of play but felt like every other one at Pull A Part. When it did change the idle, it was when I had gone past pushing and pulling and began turning it. I sprayed some starting fluid on the shaft as well and it never did anything to really take note of.

Now, this evening's discovery of the vapor canister is exceptional. Driveability is smooth and seamless. I knew something was up when the computer kept the idle high on a long test drive. I turned it off and restarted it. It now starts immediately and idles smoothly at the right rpm. It no longer burns my eyes or permeates my clothes when I stand behind it. The exhaust has a healthy ring to it. Damn, I actually look forward to driving it tomorrow!

Don't just check the vapor canister lines. Check the can too!

Thanks all. Now I can think about shocks and the bald spots on the roof!

cancritter
03-02-2009, 07:18 PM
funny,,,had mine disconeted "canister line"..truck ran fine without but was thinking l'll keep re milage ect and a bumch of other things l dont know about...after readin this will definitley be keepin...speacialy after takein steel wool to line...nice and shiney now :O)

Jasper911
03-05-2009, 07:47 PM
Grim update

Truck running better but still not right and still getting code 32. Drive for 10 miles or so and I get the light. Also, kinda doggy on the highway, does not run perfectly smooth and lock up (often premature(32mph)) makes it even worse. Have tried a fourth, known to be good, sucked on by me, oem egr valve. But still the same conditions.

Incidentally, the Autozone egr would not hold vacuum and my other oem egr was stuck in the opposite position and held no vacuum.

Bummin! Getting sick of this. Hate my truck.

Jasper911
03-16-2009, 04:02 PM
Still fighting the demons!

tpulliam79
03-16-2009, 05:20 PM
at this point i think im gonna live with it for now, had surgery on my right arm so for now its to be continued

tpulliam79
04-16-2009, 08:20 AM
well now i feel dumb after all that has gone in to this truck i noticed it looks as if the balancer may have slipped so now im wondering if because of that i cant get the timing right and that could be the whole issue. I am having the balancer , distributor, crank seal, and cv done this weekend so i will update after that.

20chevy00
04-16-2009, 09:18 AM
i saw a post on here about someones engine stumbling when idling. They changed the distributor gear and that fixed the problem. My tahoe does the same stumbling type stuff. I ordered a new gear this week and will be replacing it to see if that is the culprit. good luck.

tpulliam79
04-19-2009, 11:09 PM
well the balancer and new distributor went in and it runs stronger and we thought we had the jumpy idle fixed let it run for 20 min no issues , got in the truck gave it some gas for a minute and then it went right back to the searching for idle. electreical current is good now im thinking its got to be fuel delivery of some type, any one have an idea why it would run so good until its revved then back to the crappy idle?

loafycleetus
04-20-2009, 02:39 AM
dumps fuel at idle because the vacuum pressure is off. he never did check the fuel pressure.

what is the fuel pressure then? has the kinked line been fixed?

tpulliam79
04-20-2009, 07:36 AM
the line has not been fixed but i don't think its the issue. all the work and testing the first mechanic did is moot as he said the distributor and egr were fine , I found the egr was shot and after pulling the distributor i don't know how the truck was even running, so all he told me is not safe to think was right so I am going to ohm out my injectors, and try to check them for leaks, then try to find a fuel pressure tester that will work with my tbi, It just baffles me because it ran so great until i revved it then it went right back to the surge? the fuel return line is the one that's kinked but its not that bad and fuel can still go through it. if all checks out im thinking maybe the hose on the fuel pump that's known for going south?:sniper: :thud:

mtrmike55
04-20-2009, 07:43 AM
Checking the fuel pressure WITHOUT fixing the return line kink will do you no good. The return line problem must be repaired. Have you checked the "idle air rate"? This is the adjustment for the throttle plate opening at idle. The adjustment screw is hidden by a plug and usually is not adjusted. If the plug has been removed than it has probably been adjusted, sometimes wrongly , to try to correct an idle problem.

tpulliam79
04-20-2009, 07:51 AM
Checking the fuel pressure WITHOUT fixing the return line kink will do you no good. The return line problem must be repaired.


its not kinked shut just slightly twisted, i dont see how it would make a difference? i will see if i can get my buddy to go to the yard with me so I can have him crawl under and get one for me, i cant crawl under stuff just yet, hell I had my wife under the truck with me to do the starter ( one arm doesnt get it done.)

tpulliam79
04-20-2009, 08:29 AM
anybody know, do I have to drop the tank to replace the fuel return line from the tbi?

NEUMANNZZ
04-20-2009, 09:06 AM
starting from the beginning:

sensors:

iac valve: for smooth cycling passage clear of carbon, no wiring or connector issues, iac valve should cycle with diagnostic terminal jumped pin A to B, ignition on engine stopped. using scan tool, IAC counts at idle in correct range 5-30 in closed loop. if out of range check for vacuum leaks.
tps sensor: smooth linear response, no dead spots or voltage spikes. checked with scan tool or multimeter, around .5 to around 5 vdc at WOT.
coolant temp sensor: well above 1000 ohms when cold. around 100 ohms when hot. ensure proper thermostat is used. cooling sytem operating properly?
map sensor(with no vacuum leaks or wiring/connector issues) disconnect electrically. run vehicle? results?
o2 sensor: (wiring repaired with solder) check with scan tool cold then when in closed loop.

electrical:

wiring: check to ensure computer is grounded to engine(less then one ohm) and no variation to readings.
Check battery cables.
check for intermittent power/ fuzible links.
last resort check continuity for every single wire connected to ECM.

ensure alternator voltage is steady. if not test alternator and wiring/connections.

ignition:

check timing. ensure timing advances when engine revved.
check spark plug wires cap/rotor. also check wires and connectors for continuity.
est wire disconnected? test drive? results? if better
check coil and pickup coil with ohm meter use test in the manual. tests pass see map sensor.

fuel:

check for leaking injectors. ignition on,engine stopped. should be no leaks.
spray pattern when running should be a fine mist with cone shape barely seen. droplets okay. both injectors equal. if not check wiring continuity to injectors. check ignition control module(test multiple times.)
check fuel pressure when hot and when cold at idle. should be no variation greater then 2 psi. if so check fuel pump ground/wiring/connectors/regulator diaphram and spring.


emmissions:

check for fuel in vapor canistor.
check for overpressurization in gas tank.
egr valve isolation, remove and block passage. test drive.
check pcv valve for proper operation.
check for exhaust leaks.
Smog pump for proper operation. no leaks.


mechanical:
unusual drag on belt
check pulleys
compression test.
broken motor mounts.

other:

A/C compressor stuck on or if on high pressure switch faulty.
check park/neutral switch

NEUMANNZZ
04-20-2009, 09:07 AM
anybody know, do I have to drop the tank to replace the fuel return line from the tbi?

i wouldnt mess with the fuel return line unless your pressure is unstable.

tpulliam79
04-20-2009, 01:28 PM
what should the continuity be of the injectors and the wiring? also i moved the park neutral switch all the way one way and it seems to have smoothed out a little? Could very well be coincidence .

tpulliam79
04-20-2009, 07:49 PM
any one know the continuity of the injectors and wires? both checked in at 2 and the wires had one: 1325 and the other 1190? are these numbers right? also where is the ground for the fuel pump located thanks. also the park neutral switch has two connectors and i believe from the pics online both spots on the switch should have male connectors for the connector to slide on to and there are none for one of the connectors?

mtrmike55
04-21-2009, 05:51 AM
The fuel pump ground is a black wire that comes from the sending/pump assembly and is bolted to the top of the left frame rail near the tank. 13mm bolt ,I think.

tpulliam79
04-21-2009, 07:52 AM
any body know what the continuity should be on the injectors? and on the wires going to the injectors?

tpulliam79
04-21-2009, 10:12 AM
well I replaced neutral switch as it was bad and it helped a little , fixed the reverse light issue by adjusting the bar off the column, and it didn't change, It runs great until gas is applied then after you let off it starts the chugging ( not nearly as bad now) at this point i'm thinking the return line may have something to do with it. the way it is twisted I am wondering if once too much gas tries to go through it if its going back into the tbi and messing with it. I am going to take it off and see if this hose place in town can repair it, if not off to the yard i go and last effort ill pay 70 for a new one from the napa store. I will post back with results.

Cheyenne'88
04-21-2009, 10:26 AM
I've read on here that some guys pinch that return line a little to raise fuel pressure. (poor man's AFPR)
Haven't read the whole thread, have you checked the fuel pressure?

NEUMANNZZ
04-21-2009, 10:45 AM
the injectors are switched to ground by the ecm to fire. wires from injectors to ecm continuity should be under 1 ohm.

dont know what the injectors are supposed to ohm out at.

red and white wires are 12vdc. come from the inj a-b fuse. dark green and dark blue go to the ecm where they are switched/pulsed to ground via injector drivers.

tpulliam79
04-21-2009, 06:06 PM
well after getting the return line repaired i lost my keys 4 hours later I found them:whatever: . got the return line back on and so far so good:rocking: , at idle it idles good just a little searching ( way better and I cant get it to do it ), it doesn't try to die anymore. when put in to gear it searches for a minute but then steadies out, wondering if from being kinked for so long the computer may think it needs less fuel? I am not convinced its solved yet but ill know in a few days....., I hope its fixed but we will see. before it was more in park now its just a little when first put in gear.

NEUMANNZZ
04-21-2009, 06:21 PM
:cool:

BigBody90
04-21-2009, 08:41 PM
Do the TBI computers learn like that? If so, could you just unhook your battery cables for 10 munutes to reset it?

tpulliam79
04-22-2009, 07:15 AM
Do the TBI computers learn like that? If so, could you just unhook your battery cables for 10 munutes to reset it?

probably could just unhook the battery but after yesterdays fiasco with getting the truck unlocked and not having keys ( alarm was going off for about 10 min and more off and on) I want to give the neighbors a break:rocking:

tpulliam79
04-27-2009, 07:04 AM
well after a few days of driving, problem is still gone.. it searches a little bit at idle in gear but nothing like before, truck doesnt act like it wants to die anymore, well at least I know every sensor and all secondary ignition should be good for a while as they are all new in the last year.

layn6015
05-25-2009, 11:15 AM
If you are still looking for a shop I took my 94 sierra to wholesale motors in the valley and they put a crankshaft kit and timing chain in it,and did a good, affordable job. I usually do my own work, but this was out of my league. I live on the west side of spokane

Jasper911
06-14-2009, 05:51 PM
Still fighting mine. Swapped my tbi with a known to be good one and the truck is bout the same. I'm tired of this s--t.

Does the neutral switch really make any difference? Or the PRNDL adjustment? The neutral switch might be the only electric part I haven't changed!

tpulliam79
10-13-2009, 03:34 PM
alright back at it again , the truck runs fantastic when in park or driving down the road, but when I put it in reverse or drive ( worse in reverse) from park it almost dies then revs back up? all sensors are new and I mean all any ideas?

NEUMANNZZ
10-13-2009, 04:49 PM
check voltage at coil, ignition on, engine stopped and in park.
should be 12vdc. put it in reverse. any spikes or drop in voltage. same for drive. might just be the park/neutral switch. does it start in neutral?

maybe cycle the tilt steering in different positions, might help.

tpulliam79
10-14-2009, 08:21 AM
i will check the voltage today and see if it starts in neutral , I replaced the switch about 2 months ago.i just changed the coolant temp sensor and thermostat with the proper ones and now the truck gets up to temp but still tries to die when put into gear, I also changed the plugs and gapped them to spec , and it got worse?

214tattooguy
10-14-2009, 03:41 PM
check that saftey switch again my was doing that and i just had to get it adjusted better. and fixed my reverse lights too. they come on when i have the needle on the R.

The_Ogre25
10-14-2009, 04:40 PM
I know you have already cleaned the IAC, but did you just spay it or did you clean it off and swab out the passage. I sprayed mine out twice searching for the fix for a bad idle. Finally pulled it out and wiped off the IAC pintle gently until it was spotless and then used q-tips and carb cleaner to clean the IAC passage until the swabs cam out clean and the passage was clean.

tpulliam79
10-14-2009, 08:17 PM
I know you have already cleaned the IAC, but did you just spay it or did you clean it off and swab out the passage. I sprayed mine out twice searching for the fix for a bad idle. Finally pulled it out and wiped off the IAC pintle gently until it was spotless and then used q-tips and carb cleaner to clean the IAC passage until the swabs cam out clean and the passage was clean.

I have put a new one in and had the intake off multiple times and cleaned all the passages. i will try to re adjust the safety switch, and go from there. the truck runs great except for the blip at idle and when shifting into gear after warmed up. if it werent for emissions I wouldnt even bother

BigBody90
10-14-2009, 08:35 PM
Am I hearing this right. Having a bad or non working safety neutral switch causes a bad idle?

tpulliam79
10-15-2009, 09:10 AM
also I know tbi injectors click but should I be able to hear them clearly from inside the truck while driving? I have the factory air box and I can hear them get louder as I speed up?

NEUMANNZZ
10-15-2009, 09:36 AM
also I know tbi injectors click but should I be able to hear them clearly from inside the truck while driving? I have the factory air box and I can hear them get louder as I speed up?
they are pretty noisy, especially if your using an open element filter.

tpulliam79
10-15-2009, 09:47 AM
not an open element just the factory setup, so this loud of a tick is ok? it can be heard over my exhaust. and I have checked everything else it is definitely the injectors.

maddmaxx65
10-15-2009, 08:09 PM
if you can hear the injectors you need a separator between the supply and return lines - me 94 blazer that i got from the original owner had a crate motor swap and someone left off the line separator and the constant racket drove me nuts - sounded like a fan was running when in fact it was the 2 lines rubbing together - after the separator it quieted down but was still able to hear it - i then split some 3/8 air line and slid over both lines securing them with some zip ties and now all is quiet:head:

tpulliam79
10-16-2009, 09:14 AM
i have the separator its definitely the injectors clicking

VOLTAGExDT
05-12-2011, 09:08 PM
Hello all,

First I am somewhat of a Noob. I am mechanically inclined, however when it comes to what this or that might be or what causes this or that. Ya im a noob.

And thats why I am here.

My issue is that i also have a very rough idle.. truck runs great but at idle it seems like its misfiring, and if im coming to a stop and engage the clutch 30% of the time it dies out.

What I have done so far.

Cleaned out carborator (if thats not what it is please give me the proper term or name) using carb cleaner
did a full tune up:
Cap, rotor, plugs, air filter, and plug wires

Today i was told to try the o2 sensor.
So i went to take off the o2 sensor to bring it with me to auto parts store (so i get the right one) and there wasnt even a wire on it.
Now i dont mean to say it was un plugged. I mean some one cut the wire off of the sensor completely.
Furthermore the wire is no where to be seen.

So i re-ran a new wire from the ecm to a brand new o2 sensor.

Still same idle issue.

91 Chevy K1500
5.7 v8 Manual

One final note..
There is a tube that runs from the vapor canistor (i think) to a sensor or solenioid.. and out of that it runs to under the carb.. now this sensor or solenoid seems to have had a plug in at one time. but again it has nothing plugged into it at all, nor is there a plug to be seen.

Thank you.

cheyenne264
05-15-2011, 10:25 AM
You might try the Electronic Spark Timing module. I had one this week that wouldn't idle and diag led to the EST module. Especially since you said it's worse when cold the timing is going to have to be different than when hot. The EST module is on the passenger side of the engine to the front of the t-bod and it has a 5 terminal connector.