HELP! GMC Suburban misfire Vortec 5.7
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HELP! GMC Suburban misfire Vortec 5.7
Well, gentlemen, I have come to this forum because my shop who has been working on this GMC Suburban, 4x4 tow package, Vortec 5.7 literally!! are stumped.
June of 2017, new top end. 229,000 miles. Ran fine. Aug of 2017 under a minimal load, the engine out of the blue began to misfire, bog, popping out the exhaust when you floor it, misfire idle. It acted like cylinders were dropping.
January 2019. 1000 miles. STILL misfires. Shop that originally did the work has spent countless hours on this. EVERYTHING has been changed. Yes, everything multiple times. MAF--(4), 02's (dealer), EGR, MAP, TPS, distributors (4-used from known good running Yukons), Fuel pumps (4--Airtech, Delphi, Bosch and now a Delco Remy), Injection system (3) O'Reilly, Napa, and now a Delco Remy upgrade. Fuel filter changed. 12v at the pump. No kinks in the gas lines. 50lbs at idle. 55ish at throttle pop.
Computer (rebuilt reflashed) we did the learn yesterday and cleared the 1236 code. Timing was at 5. Scan tooled it back to 0. Idle was worse with a slight misfire.
To set a code, I took the hog out for a drive. 50 miles. It misfires all over the place when pulling away from a stop sign. Get it up to 2000 it pulls like a scalded ape. , as the trans upshifts into overdrive, its misfiring again. NO CODES.
The exhaust was dropped at manifolds, no restrictions still misfiring. Cats are magnaflow and the muffler is a flowmaster.
Countless cans of brake cleaner sprayed over the connections from the MAF to the TB to EGR to the plastic cover over the injection system.
In Aug 2017 something failed abruptly. It was running fine, then bang, misfire. No hint, no come and go misfire, just bang it was there. Like a component failed.
No shop wants this heap. They all say too many things to check, too much $$$ and time involved to diagnose. The shop that it is in now, and has been for 6 months.
Yeah they are not perfect but I've known the owner for 20 years. He is trying.
Compression is 120-130 all around btw.
Other than changing the differential oil, and rear lug nuts on the rims, we are at the point. the Suburban will be towed back to my house, and parked. It wont run. It starts, but driving it is a pain. The misfiring and stumbling. It just won't cough up a code to tell me what the heck to look at.
Scanner on the misfire section showed misfires all over the place. Nothing consistent. So that was no help.
Any ideas? Vacuum gauge shows 18 at idle, nothing indicating anything but a strong motor.
I think it is fuel pressure. It feels like low fuel pressure when pulling away from a stop light. I think there has to be a way to FORCE this Delco to push a higher number of PSI to the injection system. I saw once that a K3500 which used the same motor and tank, uses a fuel pump that runs 70-114. At this point we will try anything.
June of 2017, new top end. 229,000 miles. Ran fine. Aug of 2017 under a minimal load, the engine out of the blue began to misfire, bog, popping out the exhaust when you floor it, misfire idle. It acted like cylinders were dropping.
January 2019. 1000 miles. STILL misfires. Shop that originally did the work has spent countless hours on this. EVERYTHING has been changed. Yes, everything multiple times. MAF--(4), 02's (dealer), EGR, MAP, TPS, distributors (4-used from known good running Yukons), Fuel pumps (4--Airtech, Delphi, Bosch and now a Delco Remy), Injection system (3) O'Reilly, Napa, and now a Delco Remy upgrade. Fuel filter changed. 12v at the pump. No kinks in the gas lines. 50lbs at idle. 55ish at throttle pop.
Computer (rebuilt reflashed) we did the learn yesterday and cleared the 1236 code. Timing was at 5. Scan tooled it back to 0. Idle was worse with a slight misfire.
To set a code, I took the hog out for a drive. 50 miles. It misfires all over the place when pulling away from a stop sign. Get it up to 2000 it pulls like a scalded ape. , as the trans upshifts into overdrive, its misfiring again. NO CODES.
The exhaust was dropped at manifolds, no restrictions still misfiring. Cats are magnaflow and the muffler is a flowmaster.
Countless cans of brake cleaner sprayed over the connections from the MAF to the TB to EGR to the plastic cover over the injection system.
In Aug 2017 something failed abruptly. It was running fine, then bang, misfire. No hint, no come and go misfire, just bang it was there. Like a component failed.
No shop wants this heap. They all say too many things to check, too much $$$ and time involved to diagnose. The shop that it is in now, and has been for 6 months.
Yeah they are not perfect but I've known the owner for 20 years. He is trying.
Compression is 120-130 all around btw.
Other than changing the differential oil, and rear lug nuts on the rims, we are at the point. the Suburban will be towed back to my house, and parked. It wont run. It starts, but driving it is a pain. The misfiring and stumbling. It just won't cough up a code to tell me what the heck to look at.
Scanner on the misfire section showed misfires all over the place. Nothing consistent. So that was no help.
Any ideas? Vacuum gauge shows 18 at idle, nothing indicating anything but a strong motor.
I think it is fuel pressure. It feels like low fuel pressure when pulling away from a stop light. I think there has to be a way to FORCE this Delco to push a higher number of PSI to the injection system. I saw once that a K3500 which used the same motor and tank, uses a fuel pump that runs 70-114. At this point we will try anything.
Last edited by Rusty Gringo-Person; Jan 22, 2019 at 7:21 AM.
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Welcome to the forum. Sounds like it might be ignition related. Have you replaced anything in the distributor, coil, spark plugs, spark plug wires? Might list the model year to assist others in helping also.
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Long list of what has been replaced. 4 pumps, 4 MAF maybe 5, at least 4 maybe 5 distributors, map, tps (2), 02's are GM bought,
pump in it is a Delco Remy
spider injection (3 times) what is in it now is STANDARD, what we pulled is Borg Warner. They are the upgraded ones with the injectors at the nozzles.
Yesterday a reman-computer was installed, 4 hours of learning then the variance crank sensor routine. Code 1236,
Countless caps, various spark plugs, what is in it now I believe is AC 996, secondary wire replaced twice.
Every sensor on the Suburban has been swapped. It has a slight misfire at idle, it misfires all over the place pulling away, then around 2500 it seems to pull hard,
pops out the exhaust when slowing down, I'm going to work on the harness this weekend. Tracing. Checking, Shaking. So far since Aug 2017 nothing seems to help, once in a while a new MAS seems to make it somewhat driveable, but low RPM's it misfires and bucks. Towing is impossible, Oh the engine has 230k, burns no oil, the heads have 1500 miles brand new. 120-130 compression all around.
cats are new, magnaflows--has a flowmaster exhaust
Build 4/98 Sold new in 99, California sold, long wheelbase 5.7 4x4 Suburban. With tow package
pump in it is a Delco Remy
spider injection (3 times) what is in it now is STANDARD, what we pulled is Borg Warner. They are the upgraded ones with the injectors at the nozzles.
Yesterday a reman-computer was installed, 4 hours of learning then the variance crank sensor routine. Code 1236,
Countless caps, various spark plugs, what is in it now I believe is AC 996, secondary wire replaced twice.
Every sensor on the Suburban has been swapped. It has a slight misfire at idle, it misfires all over the place pulling away, then around 2500 it seems to pull hard,
pops out the exhaust when slowing down, I'm going to work on the harness this weekend. Tracing. Checking, Shaking. So far since Aug 2017 nothing seems to help, once in a while a new MAS seems to make it somewhat driveable, but low RPM's it misfires and bucks. Towing is impossible, Oh the engine has 230k, burns no oil, the heads have 1500 miles brand new. 120-130 compression all around.
cats are new, magnaflows--has a flowmaster exhaust
Build 4/98 Sold new in 99, California sold, long wheelbase 5.7 4x4 Suburban. With tow package
Last edited by Rusty Gringo-Person; Jan 22, 2019 at 6:40 PM.
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Long list of what has been replaced. 4 pumps, 4 MAF maybe 5, at least 4 maybe 5 distributors, map, tps (2), 02's are GM bought,
pump in it is a Delco Remy
spider injection (3 times) what is in it now is STANDARD, what we pulled is Borg Warner. They are the upgraded ones with the injectors at the nozzles.
Yesterday a reman-computer was installed, 4 hours of learning then the variance crank sensor routine. Code 1236,
Countless caps, various spark plugs, what is in it now I believe is AC 996, secondary wire replaced twice.
Every sensor on the Suburban has been swapped. It has a slight misfire at idle, it misfires all over the place pulling away, then around 2500 it seems to pull hard,
pops out the exhaust when slowing down, I'm going to work on the harness this weekend. Tracing. Checking, Shaking. So far since Aug 2017 nothing seems to help, once in a while a new MAS seems to make it somewhat driveable, but low RPM's it misfires and bucks. Towing is impossible, Oh the engine has 230k, burns no oil, the heads have 1500 miles brand new. 120-130 compression all around.
cats are new, magnaflows--has a flowmaster exhaust
Build 4/98 Sold new in 99, California sold, long wheelbase 5.7 4x4 Suburban. With tow package
for usual misfire problems click here
pump in it is a Delco Remy
spider injection (3 times) what is in it now is STANDARD, what we pulled is Borg Warner. They are the upgraded ones with the injectors at the nozzles.
Yesterday a reman-computer was installed, 4 hours of learning then the variance crank sensor routine. Code 1236,
Countless caps, various spark plugs, what is in it now I believe is AC 996, secondary wire replaced twice.
Every sensor on the Suburban has been swapped. It has a slight misfire at idle, it misfires all over the place pulling away, then around 2500 it seems to pull hard,
pops out the exhaust when slowing down, I'm going to work on the harness this weekend. Tracing. Checking, Shaking. So far since Aug 2017 nothing seems to help, once in a while a new MAS seems to make it somewhat driveable, but low RPM's it misfires and bucks. Towing is impossible, Oh the engine has 230k, burns no oil, the heads have 1500 miles brand new. 120-130 compression all around.
cats are new, magnaflows--has a flowmaster exhaust
Build 4/98 Sold new in 99, California sold, long wheelbase 5.7 4x4 Suburban. With tow package
for usual misfire problems click here
This seems like a hard nut.
So, you have changed your ECU with another one, and there was no change?
Did you change your crankshaft position sensor (althought this is a long-shot)?
You have mentionee that engine harness has not been changed yet. This might be your source of problems. Maybe it would be best to swap it out.
Tnx!
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OK I held my breath for 3 days. I shopped around town for another shop. The one who has been working on all of my cars, trucks, jeeps, (5) Ford Exploders, and the GMC could not figure this out. They are the ones who put the heads on. I am serious about how many pumps have been installed. How many spiders have been installed. How many MAF's...still to get a misfire that got worse and worse.
I found shop after shop who would not take this project on. I guess they are not hungry nor competent. FINALLY--a 40 year shop I landed in his office. Mike and I talked. for well into an hour about all the possibilities involved here.
He pulled a roller lifter out from his desk, handed it to me. The roller was worn. GM has a service bulletin that when you change heads, to do the lifters too. I do not know if the lifters were changed in June 2017 when the new heads were installed. All I know it was running great then BANG the Suburban went south. And has been since 2017.
One of his younger techs was in the office. "Mike, I want that Suburban, I can fix it." The two chatted about getting buried into this project, but this kid diagnosed the Viper sitting out front, he fixed a 5.3 Suburban that the dealer could not, .....SO----it was towed.
It hardly moved. Popping, you would think it was running on 2 cylinders.
48 hours later the cell phone rang. Owner to me, "Pull over, we need to talk." I expected the worst. Bad lifter ruined the cam. $$$$ into an already money pit 99 GMC Suburban with 230k
"well, you wanna know what is wrong?" I held my breath, Computer. We reflashed your rebuilt one, then reflashed your OEM. The OEM has a fault on one of the chips, that was the original problem.....
Distributor connection was worn. Too many times previously noted shop yanked the connection on it probably swapping in dizzy after dizzy. That repaired. #8 fouled out, and the ignition wire all burnt at the end. The cap is a low-end cheapo from Walmart maybe. Once Delco Remy was installed it purrs.....the kid is known as a
"Suburban Whisperer". He's on my Christmas list.
This shop when I pulled in with the tow truck behind me, was packed with newer high-end cars. AMG's, Viper, Vettes. He did not need my business. But it is repaired and I pick it up today. $800- 800 well spent to get the tank to a competent shop. Not the bottom feeders who swap parts.
Oh they did what is called a running compression test. I never heard of this. Shradder valve removed, Start the engine, watch the compression. Next cylinder. Then next. Once it was all completed they could see that the cam, the heads and gaskets were solid...
Fixed. Now what to do with a dozen MAF's, fuel pumps, distributors.....
I found shop after shop who would not take this project on. I guess they are not hungry nor competent. FINALLY--a 40 year shop I landed in his office. Mike and I talked. for well into an hour about all the possibilities involved here.
He pulled a roller lifter out from his desk, handed it to me. The roller was worn. GM has a service bulletin that when you change heads, to do the lifters too. I do not know if the lifters were changed in June 2017 when the new heads were installed. All I know it was running great then BANG the Suburban went south. And has been since 2017.
One of his younger techs was in the office. "Mike, I want that Suburban, I can fix it." The two chatted about getting buried into this project, but this kid diagnosed the Viper sitting out front, he fixed a 5.3 Suburban that the dealer could not, .....SO----it was towed.
It hardly moved. Popping, you would think it was running on 2 cylinders.
48 hours later the cell phone rang. Owner to me, "Pull over, we need to talk." I expected the worst. Bad lifter ruined the cam. $$$$ into an already money pit 99 GMC Suburban with 230k
"well, you wanna know what is wrong?" I held my breath, Computer. We reflashed your rebuilt one, then reflashed your OEM. The OEM has a fault on one of the chips, that was the original problem.....
Distributor connection was worn. Too many times previously noted shop yanked the connection on it probably swapping in dizzy after dizzy. That repaired. #8 fouled out, and the ignition wire all burnt at the end. The cap is a low-end cheapo from Walmart maybe. Once Delco Remy was installed it purrs.....the kid is known as a
"Suburban Whisperer". He's on my Christmas list.
This shop when I pulled in with the tow truck behind me, was packed with newer high-end cars. AMG's, Viper, Vettes. He did not need my business. But it is repaired and I pick it up today. $800- 800 well spent to get the tank to a competent shop. Not the bottom feeders who swap parts.
Oh they did what is called a running compression test. I never heard of this. Shradder valve removed, Start the engine, watch the compression. Next cylinder. Then next. Once it was all completed they could see that the cam, the heads and gaskets were solid...
Fixed. Now what to do with a dozen MAF's, fuel pumps, distributors.....
