Misfire

[Oathkeeper]

2001 Tahoe LS 5.3 I keep getting a misfire code in either 4 or 7 also have the code for primary secondary circuit on both of those cylinders, I've replaced plugs,wires,the ignition coil sub harness,map sensor,, replaced knock sensor and intake gaskets, valve cover gaskets,did a compression test and leak down test everything was right, what throws me off is if either cylinder misfires I can disconnect the connector,wait a minute and it works like it should until I turn the Tahoe off or I hit a bump in the road, and now I smell gas fumes while the car is running, idk what else to do,I've tried finding where my grounds are located but no luck ,any advice would greatly be appreciated

 

[TollKeeper]

Im a little out of date on these PCM's, but it almost sounds like the Coil Driver in the PCM has failed, or is failing. You have done most of the things I would do to test..

There are 2 more tests, and for the first one on both of your problem cylinders, is going to be a pain in the a$$. A engine HOT compression test.

The second test is a injector test, which either means using a tech2 or taking out the injectors and having them tested.

Personally, I would start with the second test, since you have the smell of gas. Like the injector is getting stuck open/closed, depending on its mood.

 

[Fless]

What are the specific codes that are being set?

Ditto on the injector balance test @TollKeeper mentioned.

Suggestions: pull the PCM connectors off and inspect for water intrusion and pin cleanliness. Have any coils been swapped? If not, mark the coils in their numbered positions and swap 4 or 7 (whichever one you're testing) with one from a known good cylinder. See if the misfire follows.

 

[iamdub]

2001 Tahoe LS 5.3 I keep getting a misfire code in either 4 or 7 also have the code for primary secondary circuit on both of those cylinders, I've replaced plugs,wires,the ignition coil sub harness,map sensor,, replaced knock sensor and intake gaskets, valve cover gaskets,did a compression test and leak down test everything was right, what throws me off is if either cylinder misfires I can disconnect the connector,wait a minute and it works like it should until I turn the Tahoe off or I hit a bump in the road, and now I smell gas fumes while the car is running, idk what else to do,I've tried finding where my grounds are located but no luck ,any advice would greatly be appreciated

I'm with @Fless on revealing the codes and testing the coils themselves. It's odd that two coils would fail at or near the same time. What connector are you disconnecting for a minute? With the problem returning after hitting a bump, it could be an intermittent open or short in the PCM or the harness. Maybe even a faulty or loose crank or cam position sensor. Although that'd probably throw a correlation code.

Where do you smell gas fumes? Stronger near the rear wheel wells? Is rust an issue where you live?

 

[Snowbound]

Hitting a bump leads me to believe it’s a connector issue or maybe a chaffed wire. While is sitting there running see if you can wiggle the harness around and it causes the issue. The gas smell could be from the lack of spark in either or both cylinders sending fuel out the exhaust. That’s not good for the cat either.

 

[rockola1971]

Sounds like a broken wire(s) going to affected cylinder's coils. Those wires can break their copper stranded wires but look perfectly fine from the outside. Usually you can feel the stiffness gone when your fingers come across the break(s) while running them down the wires. A really common problem for DBW harness to the throttle body motor.

 

[Oathkeeper]

What are the specific codes that are being set?

Ditto on the injector balance test @TollKeeper mentioned.

Suggestions: pull the PCM connectors off and inspect for water intrusion and pin cleanliness. Have any coils been swapped? If not, mark the coils in their numbered positions and swap 4 or 7 (whichever one you're testing) with one from a known good cylinder. See if the misfire follows.

I tried swapping before replacing the 2 coils ,and the misfire stayed in 4&7

What are the specific codes that are being set?

Ditto on the injector balance test @TollKeeper mentioned.

Suggestions: pull the PCM connectors off and inspect for water intrusion and pin cleanliness. Have any coils been swapped? If not, mark the coils in their numbered positions and swap 4 or 7 (whichever one you're testing) with one from a known good cylinder. See if the misfire follows.

I swapped them around before replacing the coils on 4&7.. the misfire stayed , so the codes I just now got are p0300,p0327,p0332,p0354,p0357, and p0650

 

[Oathkeeper]

I'm with @Fless on revealing the codes and testing the coils themselves. It's odd that two coils would fail at or near the same time. What connector are you disconnecting for a minute? With the problem returning after hitting a bump, it could be an intermittent open or short in the PCM or the harness. Maybe even a faulty or loose crank or cam position sensor. Although that'd probably throw a correlation code.

Where do you smell gas fumes? Stronger near the rear wheel wells? Is rust an issue where you live?

I smell the fumes while in my car ,and the sub harness that connects on top of the coils

 

[Oathkeeper]

Hitting a bump leads me to believe it’s a connector issue or maybe a chaffed wire. While is sitting there running see if you can wiggle the harness around and it causes the issue. The gas smell could be from the lack of spark in either or both cylinders sending fuel out the exhaust. That’s not good for the cat either.

I tried moving the harness around while running, I've even opened up the harness looking for a short in the wiring... And I don't have cats

 

[Oathkeeper]

Sounds like a broken wire(s) going to affected cylinder's coils. Those wires can break their copper stranded wires but look perfectly fine from the outside. Usually you can feel the stiffness gone when your fingers come across the break(s) while running them down the wires. A really common problem for DBW harness to the throttle body motor.

Ok thanks I'll start that this weekend after this rain stops