Stutter/ Stumble/ Misfire Transmission Slipping? 97 Z71 Vortec 350

[southmainmotors]

I have spent a fortune trying to fix this problem. The truck has an intermittant possible misfire. It is most noticeable in overdrive when the torque converter is in lockup. I guess that is because there is more of a direct correlation with engine performance and drivetrain speed. I can sometimes feel it at other speeds, it is just not very noticeable. I have learned that I can actually make it occur. What I do is accelerate then hold the truck at 50 MPH with the truck in overdrive. I then roll into the throttle a little bit. Then as I slowly come back out of the throttle, "clunk". What appears to be a severe miss. I think the engine actually stumbles, but it is so quick, the tack does not move. I have already replaced the distributor cap, rotor, plugs to AC Delco, Wires and Coil. Any help would be greatly appreciated. The truck has no trouble codes, and I had it at the dealership today, and they charged me 79 bucks to tell me they can't figure it out. Thanks again,
Donnie

[N0DIH]

sounds like what a friend of mine's 98 K1500 Burb does. I can do it at a lot of speeds from 40-65 (what I tried it at) and it is pretty violent in my book. I suspect it is the converter itself, but hard to prove either way. If I apply the brake slightly to disable TCC, it never happens. So distinctly TCC related.

Try this, can you make it do it in 3rd gear? It will lockup in 3rd, see if it still does it.

I have spent a fortune trying to fix this problem. The truck has an intermittant possible misfire. It is most noticeable in overdrive when the torque converter is in lockup. I guess that is because there is more of a direct correlation with engine performance and drivetrain speed. I can sometimes feel it at other speeds, it is just not very noticeable. I have learned that I can actually make it occur. What I do is accelerate then hold the truck at 50 MPH with the truck in overdrive. I then roll into the throttle a little bit. Then as I slowly come back out of the throttle, "clunk". What appears to be a severe miss. I think the engine actually stumbles, but it is so quick, the tack does not move. I have already replaced the distributor cap, rotor, plugs to AC Delco, Wires and Coil. Any help would be greatly appreciated. The truck has no trouble codes, and I had it at the dealership today, and they charged me 79 bucks to tell me they can't figure it out. Thanks again,
Donnie

[Pauly]

Possible worn distributer gear, look for signs of knifedging on the dist gear teeth. I spend a ton of money on a misfire in lockup, injectors cap rotor blah blah blah ad nauseum and it ended up a damn inexpensive dist. gear.

peace
Pauly

[96 Chevy 2500]

I have a 96 chevy k2500 350 it has the exact same problem i replaced the plugs, wires,cap, tps, rotor, fuel pump, and fuel filter. I had the transmission completly rebuilt about 11k miles ago. It didnt fix the miss. I took it to Gm yesterday and they said it was a worn distributer gear, they replaced that and the problem is still there. I droped it off this mourning and they have worked on it all day and have still not come up with anything.

[justy]

We just finished a truck that had that trouble it had a sticky valve. That you would only notice the misfire at low rpms.

[mluters]

My suburban does the same thing - I have a 96 Burb that hesitates/misses at freeway speeds in overdrive when placed under load - like going up a small hill or passing. As soon as the tranny downshifts or I take it out of overdrive the hesitation is gone and it charges right up the hills without any troubles at all. It never occurs at slower speeds or other gears - only in O/D at freeway speeds with a load on the eng/tranny. I have replaced fuel filter and spark plugs with no luck. Also, I hooked up a scanner and no codes have shown up. Some times I think this hesitation may be worse when the Burb is warmed up or hot - seems to do it a little less when it's cold. I will now try the dist gear as others have mentioned and report back.

[N0DIH]

I have had this situation on my 91 Bonneville, 1 time it was fuel pump, just getting weak, it was down to around 30 psi and it did that. And the other, was weak coils/plugs/wires. It always reared its head on the coils/plugs/wires in the dead cold of winter. Easy way to spot was cold drivability wasn't too good, but once warm was ok. But as it progressed, higher load (like OD at 45 mph TCC locked, gentle throttle, but enough to accelerate, maintaining TCC lock) would buck and sputter. Kick out of OD and it was fine like nothing was wrong.

My suburban does the same thing - I have a 96 Burb that hesitates/misses at freeway speeds in overdrive when placed under load - like going up a small hill or passing. As soon as the tranny downshifts or I take it out of overdrive the hesitation is gone and it charges right up the hills without any troubles at all. It never occurs at slower speeds or other gears - only in O/D at freeway speeds with a load on the eng/tranny. I have replaced fuel filter and spark plugs with no luck. Also, I hooked up a scanner and no codes have shown up. Some times I think this hesitation may be worse when the Burb is warmed up or hot - seems to do it a little less when it's cold. I will now try the dist gear as others have mentioned and report back.

[96 Chevy 2500]

I got mine back from the dealership today after they have worked at the problem for 3 days,and they said they cannot fix the problem.

[cvfd1343]

I am so glad I found this post. I just got my 4l60 put back in my 97 GMC K1500 4x4 and it is doing exactly as described above. When TCC engaged it has a hard buck. When I press the brake to keep it from engaging I can hear a light engine miss. No trouble codes.
I also have a camshaft position sensor code replaced the sensor and it has correct voltage. What gives?

[jarrodscot]

I also am getting a low rpm stumble but as soon as I give it a hair more gas it snaps out of it. Its barely there but Im a person that wants to fix something before it gets worse. So any feed back would be great. I just bought this particular truck and have a list of things to fix.

[cvfd1343]

Got my miss fixed. Come to find out when I put a test light on the camshaft sensor plug the center pin which is the signal wire was grounded and lighting the test light when I had the other end in the feed. I had just put in a rebuilt tranny and had pinched two of the wires resulting in them being grounded.

If you have a code 340 I may be able to help you sort it out. That is what I had.

[Titus1355]

Anyone that has the problem stated in the orignal post knows exactly what hes talking about. No codes or anything like that. Well l would like to kno if anyone has figured this out?

[Dupontster]

I have the same problem with my 97 1500 4.3...Just does it in overdrive...I am almost sure it is the transmission...I can take off hard and it shifts fine....Just does it going down the road in overdrive....Anyone find out a fix yet?

[1997Chevy!]

Possible worn distributer gear, look for signs of knifedging on the dist gear teeth. I spend a ton of money on a misfire in lockup, injectors cap rotor blah blah blah ad nauseum and it ended up a damn inexpensive dist. gear.

peace
Pauly

sounds like what a friend of mine's 98 K1500 Burb does. I can do it at a lot of speeds from 40-65 (what I tried it at) and it is pretty violent in my book. I suspect it is the converter itself, but hard to prove either way. If I apply the brake slightly to disable TCC, it never happens. So distinctly TCC related.

Try this, can you make it do it in 3rd gear? It will lockup in 3rd, see if it still does it.

I have a 96 chevy k2500 350 it has the exact same problem i replaced the plugs, wires,cap, tps, rotor, fuel pump, and fuel filter. I had the transmission completly rebuilt about 11k miles ago. It didnt fix the miss. I took it to Gm yesterday and they said it was a worn distributer gear, they replaced that and the problem is still there. I droped it off this mourning and they have worked on it all day and have still not come up with anything.

I have the same problem. I assumed it was the clutches gettin worn or something. I have a slight mis at idle but only when warm. I have a new distributor in the mail. But i talked to a tranny speicalist and he says a miss could cause the tranny to do this in od or there is a electronical lock up for od and it isnt working correct or at worst case a converter. But if you have anykind of mis fix that first because a miss can cause a computer freak out.

[reddituser]

I'm amazed so many people have this problem and no one has found a solution! I have the same problem plus a persistent no 6 misfire. Has anyone tried replacing their cats? Just wondering.

[N0DIH]

If I had the truck to datalog and look at it myself probably could find. Throwing parts at it only helps you get broke. Taking to a shop that only throws parts at it, makes you more broke. Don't pay for parts that don't fix the problem, don't let these mechanics troubleshoot with your $. Sorry, getting off my soapbox.

But troubleshooting over the internet is hit or miss at best.

Find someone who can datalog it, it makes all the difference in the world seeing what is going on.

Where in WI are you reddituser?

[reddituser]

Milwaukee, but I am in north Chicago area often. I have been throwing money at my truck for some time, replacing just about everything it seems. Here's my snapshot:
Engine Load = 5.49 %
Engine Coolant Temperature = 194 °F
Fuel Trim Bank 1 Short Term = -10.156 %
Fuel Trim Bank 1 Long Term = -10.938 %
Fuel Trim Bank 2 Short Term = 7.812 %
Fuel Trim Bank 2 Long Term = 11.719 %
Intake Manifold Pressure = 6.382 psi
Engine RPM = 770.25 rpm
Speed (OBD) = 0 mph
Mass Air Flow Rate = 88.155 cfm

Symptoms:
I am losing coolant slowly
good compression
Cylinder 6 misfire
****ty MPG
obv running lean/rich on opposite banks
high idle in neutral/park (goes up to 2k then settles around 1150)
rough running/sluggish
kick/miss on the highway
rattle in one of my cats (seemingly my fault from banging on the pipe when installing new exhaust)
seemingly enginewide miss when i let off the throttle after accelerating (sporadic)

Replaced:
MAF
MAP
TPS
fuel injection conversion
plugs, wires, cap, rotor, distributor (factory timing set)
That's all I can think of now, but there was more....

Any thoughts? Taking what I can get here. My current thinking is some combination of bad intake gasket and bad cats.

[N0DIH]

You are rich on one side and lean on the other, by the looks of it, still in open loop. Has it gone into closed yet?

Try this, SWAP the O2's from L to R. See if the problem follows.

Also, are there ANY exhaust leaks from the O2 forward? That will wreak havok with fueling. Are the cats good?

Can you datalog for a while? Snapshots to me aren't terribly helpful. A good drive with the problem showing up.

I am west of Chicago at I90/I39.

Milwaukee, but I am in north Chicago area often. I have been throwing money at my truck for some time, replacing just about everything it seems. Here's my snapshot:
Engine Load = 5.49 %
Engine Coolant Temperature = 194 °F
Fuel Trim Bank 1 Short Term = -10.156 %
Fuel Trim Bank 1 Long Term = -10.938 %
Fuel Trim Bank 2 Short Term = 7.812 %
Fuel Trim Bank 2 Long Term = 11.719 %
Intake Manifold Pressure = 6.382 psi
Engine RPM = 770.25 rpm
Speed (OBD) = 0 mph
Mass Air Flow Rate = 88.155 cfm

Symptoms:
I am losing coolant slowly
good compression
Cylinder 6 misfire
****ty MPG
obv running lean/rich on opposite banks
high idle in neutral/park (goes up to 2k then settles around 1150)
rough running/sluggish
kick/miss on the highway
rattle in one of my cats (seemingly my fault from banging on the pipe when installing new exhaust)
seemingly enginewide miss when i let off the throttle after accelerating (sporadic)

Replaced:
MAF
MAP
TPS
fuel injection conversion
plugs, wires, cap, rotor, distributor (factory timing set)
That's all I can think of now, but there was more....

Any thoughts? Taking what I can get here. My current thinking is some combination of bad intake gasket and bad cats.

[reddituser]

Mechanic told me he replaced the bank 2 O2, should I still swap? No leaks that I can hear or see.

How do I know if it has gone into closed loop? How can I tell if the cats are good?

Forgot to add, fouling on all bank 2 plugs, especially bad on the no 6. Here is a pic of the number 6 after about 300 miles http://imgur.com/ukyCn

I met a guy here who has the exact same symptoms, to the T, he's replacing his intake gasket next week but I'm not holding my breath. Thanks in advance for all this help

Edit: All I have is a bluetooth thinger and Torque pro on my android. Not sure if it datalogs, just got it the other day

[reddituser]

Data logged for a quick ride around town, selected just about everything to record. Have it as an excel file.