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87 Chevy TBI 350 Idling issues

This is a discussion on 87 Chevy TBI 350 Idling issues within the C10 Forum forums, part of the General Discussion category; I unhooked mine and my truck ran better. Check engine light never came back on and fuel economy was good ...

  1. #41
    Registered User robotic_junky's Avatar
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    Re: 87 Chevy TBI 350 Idling issues


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    I unhooked mine and my truck ran better. Check engine light never came back on and fuel economy was good (13-15 mpg).
    2005 Chevy Corvette LS2 DD 105k
    1991 Firebird n/a 190k
    1987 Silverado 350 HSR 230k
    1980 Bonneville 350 Olds. diesel 198k
    1993 G20 350TBI 252k

  2. #42
    Registered User Jameslleary's Avatar
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    Re: 87 Chevy TBI 350 Idling issues

    Quote Originally Posted by ryan_thompson87 View Post
    Very possible. What would they would have done is ground the intake the match the different angle on the intake sealing surface on the heads. Get some carb cleaner and spray around the intake gaskets with it running, if it idles up, they did a ****ty job on it and the intake is leaking.
    with all due respect, the mating surfaces on small block heads are the same. The center bolt angle on the manifold is what needs to be modified.
    1986 K10 Suburban
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  3. #43
    GMC RULZZ NEUMANNZZ's Avatar
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    Re: 87 Chevy TBI 350 Idling issues

    Running with no egr valve will not kill your engine. go for it.
    O2 GMC RCSB 4.8L V8 AUTO 3.73's
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  4. #44
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    Re: 87 Chevy TBI 350 Idling issues

    Ok here's an update: I made me an egr block off plate out of my old valve. Cranked her up last night and she's burning waaay rich and hard to keep running. Timing light was left at other shop so I want be able to set the timing until tonight but I was able to keep it running long enough to blindly play around with the timing and I never could get it to clear up. I'm starting to get a little nervous. I'll know for sure after tonight but if it's not because of the timing I'm starting to wonder if this whole carb intake w/transdapt plate is gonna work. Do I need to unhook the egr valve solenoid connector or just the vacuum line that used to go to the valve and keep the connector connected to prevent the light from coming on? Also, for what it's worth right now, it threw a 33 (high maf signal) if this means anything.

  5. #45
    Registered User robotic_junky's Avatar
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    Re: 87 Chevy TBI 350 Idling issues

    Code 33 MAP sensor high voltage. Check the reference voltage supply at pin C of the MAP sensor (gray wire typically). Measure voltage between pin A (ground) and Pin C (+5 V ref) with a DVM. It should be right around 5 Vdc. With Key on engine off the MAP voltage (Pin B, light green wire typically) should read around 4.8 to 4.9 volts. If it reads the same as pin C the sensor is probably is history. Also check ground reference pin A. With everything off, measure resistance between Pin A and electrical ground (stud next thermostat). It should be fractional ohms. I hope this helps

    Another functional check – with engine idling MAP output voltage (depending on idle vacuum) should be in the neighborhood of 1.2 to 2.0 volts. If it is stuck at 5 volts check grounds and most likely MAP sensor is history.
    2005 Chevy Corvette LS2 DD 105k
    1991 Firebird n/a 190k
    1987 Silverado 350 HSR 230k
    1980 Bonneville 350 Olds. diesel 198k
    1993 G20 350TBI 252k

  6. #46
    GMC RULZZ NEUMANNZZ's Avatar
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    Re: 87 Chevy TBI 350 Idling issues

    sounds like a major vacuum leak. selenoid vacuum needs to be plugged or the line removed going to it plugged or deleted.
    O2 GMC RCSB 4.8L V8 AUTO 3.73's
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  7. #47
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    Re: 87 Chevy TBI 350 Idling issues

    Ok, I was able to set the timing last night (0 degrees) and it still wasn't wanting to idle and running really rich. Started spraying around the base gasket to check that the Transdapt adapter was sealing up ok and it was NOT! I have another adapter ordered to replace this one. Hopefully this fixes my problem. The good news is that I think this intake and adapter idea has fixed my surging problem that I've had from day one. Even though it's still not idling right, at least it's consistent now and not surging. Upon removal of old intake I could see a noticeably black residue in the centers of each gasket where he didn't use the center bolts and only silicone.

  8. #48
    Registered User Jameslleary's Avatar
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    Re: 87 Chevy TBI 350 Idling issues

    The EGR will still throw a code, regardless of whether or not you keep the solenoid hooked up. The EGR flag in the Prom needs to be unchecked to keep from throwing a code. The ECM uses the o2 sensor to confirm the change in operating conditions when it commands EGR, or upstream AIR injection...if it does not see the desired change when one of those functions are commanded, it will throw a code.
    1986 K10 Suburban
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  9. #49
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    Re: 87 Chevy TBI 350 Idling issues

    Quote Originally Posted by Jameslleary View Post
    The EGR will still throw a code, regardless of whether or not you keep the solenoid hooked up. The EGR flag in the Prom needs to be unchecked to keep from throwing a code. The ECM uses the o2 sensor to confirm the change in operating conditions when it commands EGR, or upstream AIR injection...if it does not see the desired change when one of those functions are commanded, it will throw a code.
    Depending on how much trouble it would be to get this prom tweaked, as long as it doesn't effect the way the engine performs or effect my fuel economy, I'm really not concerned about the light being on. If it will in fact effect either or both of the two, what would one have to do to get the prom recoded for "no EGR valve"

  10. #50
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    Re: 87 Chevy TBI 350 Idling issues

    Mine valve is gone, blocked off, and my truck doesn't even throw a code 32, EVER.

    87 K30-355 Vortec TBI/TH350/208/Dana 60/14FF/4.56s/Detroit/37"Bogger/Ult.TBI Mods/XtremeFI FPR vac. reference/EP241 Pump/LS1 Fans

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  11. #51
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    Re: 87 Chevy TBI 350 Idling issues

    Good to know Ryan, thanks! My new Transdapt adapter should be in by tomorrow so I should know then how everything works out. I'll let y'all know. Thanks to everyone for the help!

  12. #52
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    Re: 87 Chevy TBI 350 Idling issues

    Ok, well the new adapter came in and once again I'm back to day 1. I can't even keep her running now. 3,000 rpm and above is fine but anything below that is just crap. Running waaay to rich. I'm just at a dead end again with my pockets empty. I'm tired of shooting in the dark so I think I'm gonna make an investment in a fix that is 99.9 % guaranteed to fix my idling issues. I will probably miss the gas mileage but I think scraping this whole cursed fuel injection system and going with a carb. If I'm correct, the only thing I will need since I already have the right intake is a distributor and carb? Does anyone know if anything will need to be done to the computer for the fuel pump to still work?
    Last edited by SKYDoutCHEVY; 08-15-2011 at 06:51 AM.

  13. #53
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    Re: 87 Chevy TBI 350 Idling issues

    I wanted to come back and post the problem for anyone that might be curious. I ended up taking the truck to another mechanic and after all this time and money put into this truck he found the problem. He said I had a bad distributor ground. I'm not exactly clear on what ground this is and he didn't wanna explain his self. The only thing he would tell me was that, with his computer, he could manually override the electronic timing advance and the truck would sit and idle great but that his computer would only hold that override for 2 min. After the override cancels the truck would go back to rough idle. I didn't push the issue because, to be frank, this mechanic is a bit of an a**hole and I was just glad the truck was fixed. The only problem I am continuing to have is extreme hesitation upon acceleration ONLY until the motor warms up. But for the most part, the truck is idling and running great now! Thanks for everyone's help!

  14. #54
    GMC RULZZ NEUMANNZZ's Avatar
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    Re: 87 Chevy TBI 350 Idling issues

    distributor wiring diagram:

    http://i40.tinypic.com/330d6y9.jpg

    the distributor is grounded to the engine block via hold down bolt and bracket.
    in the distributor the icm is grounded to the distributor base via two mounting bolts(need to be corrosion free same for mating surfaces)


    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.

    ensure the module screws are grounding module to distributor base.

    the two pin connector on the distributor(C and +) should have battery voltage there. low voltage would indicate an open or a high resistance circuit from the distributor to the coil or ignition switch. For example If C terminal voltage is low and + voltage is 10 volts or more circuit from C terminal to ignition coil(coil primary) is open.
    Last edited by NEUMANNZZ; 10-04-2011 at 11:58 AM.
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  15. #55
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    Re: 87 Chevy TBI 350 Idling issues

    NEUMANNZZ, great material there. Sadly this redneck can't comprehend half of it lol. Maybe you could point me in the right direction for which of these circuits you would check first if the truck is doing this: When the engine is cold (no matter the outside air temp) it will crank after about 5 revolutions. Right at start up, the idle is high like normal and then after a few seconds it slowly decreases like normal. As long as it's idling it's fine but the slightest acceleration and it starts cutting out, almost like it's starving for fuel but fuel pressure is good. I can push the pedal on down a ways and after jerking 1 or 2 times it will eventually grab and take off like it suddenly gets a steady flow of fuel but it still feels a little sluggish upon acceleration. Changing from 1st to 2nd, same thing but maybe not quite as bad....and then so on. It usually takes me about 3 or 4 stoplights before it starts smoothing out and then once it's warm it runs pretty much about 90%. Even after it's warm it still sometimes just feels sluggish especially at the bottom of every gear. Does this tell you anything or not really? Hey at least it's running now so if it turns out that I'll just have to deal with it, that won't be a problem but would rather it be right if possible. Thanks again for your help!

  16. #56
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    Re: 87 Chevy TBI 350 Idling issues

    did he check base timing?
    does it run better with est wire disconnected?
    plug gaps too wide?
    egr valve could be sticking. oh wait didnt you block it off?
    http://www.fullsizechevy.com/forum/g...eshooting.html
    Last edited by NEUMANNZZ; 10-05-2011 at 10:22 AM.
    O2 GMC RCSB 4.8L V8 AUTO 3.73's
    rebuilt/beefed up 4L60E(at 43,000miles)
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  17. #57
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    Re: 87 Chevy TBI 350 Idling issues

    Quote Originally Posted by NEUMANNZZ View Post
    did he check base timing?
    does it run better with est wire disconnected?
    plug gaps too wide?
    egr valve could be sticking. oh wait didnt you block it off?
    http://www.fullsizechevy.com/forum/g...eshooting.html
    Yes he said he set the timing by his computer because it had the wrong balancer on there
    It doesn't idle any better with est disconnected but I'm not sure about accelerating with it disconnected
    Plug gaps are right
    I had blocked the egr valve off when I was trying to make the carb intake work but have since had the center bolt wholes reangled on the
    fuel injection intake and am now using it again. I installed a new EGR valve

  18. #58
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    Re: 87 Chevy TBI 350 Idling issues

    i would be curious to see what base timing is really set at.
    O2 GMC RCSB 4.8L V8 AUTO 3.73's
    rebuilt/beefed up 4L60E(at 43,000miles)
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  19. #59
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    Re: 87 Chevy TBI 350 Idling issues

    Did you replace the EGR with exactly the same one? there are 2 different EGR's, one with a P in the part number and one with an N. If you swap them the truck won't run right. Just a suggestion to look at, since you changed it.

  20. #60
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    Re: 87 Chevy TBI 350 Idling issues

    Quote Originally Posted by jim_in_dorris View Post
    Did you replace the EGR with exactly the same one? there are 2 different EGR's, one with a P in the part number and one with an N. If you swap them the truck won't run right. Just a suggestion to look at, since you changed it.
    Interesting........with this being a different motor than what come stock, how would I go about finding out which valve I would need?

 

 
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