Misfires

[blazes9395]

This is an interesting problem. While it could very well be an engine problem, has anybody checked the injectors? Could be intermitent injector problems - its well known that the injector pack on these engines have had reliability issues.

[mdrush]

Truck is still at the dealership. The service manager told me they have checked both the ignition and fuel systems. Apparently the engine is out of the truck and they were waiting Friday afternoon for GM to determine whether they will try to "fix" the engine or replace it.

The Dealership also confirmed that they could not get the distributor to line up without having to slot the hold down clamp.

[mdrush]

One other piece of noteworthy info...When the technician was running diagnostics he told me that the misfire first appears at 2925 RPM on Cylinder 1 and at 3400 RPM stops on Cyl 1 and starts misfiring on Cyl 2. Backing off the acceleration causes the reverse (ie stops misfiring on Clylinder 2) and starts back on Cylinder 1.

[MT-2500]

Originally Posted by mdrush

One other piece of noteworthy info...When the technician was running diagnostics he told me that the misfire first appears at 2925 RPM on Cylinder 1 and at 3400 RPM stops on Cyl 1 and starts misfiring on Cyl 2. Backing off the acceleration causes the reverse (ie stops misfiring on Clylinder 2) and starts back on Cylinder 1.

Mdrush
That is interesting info on it.
No 1 and no 2 fires right next to each other.
What ever it is must be feeding back to the other cylinder.
A good old vacume gauge test on the engine may show something.
But it sounds like the dealer tech is really working up and beyond the call of duty on the problem.
Can you feel the missfire in engine running when it missfires?
Good luck and let us know how it goes.
MT

[mdrush]

Got my truck back from GM beginning of last week and she runs great. They replaced they ended up replacing the CAM shaft, CAM gear, Timing chain, CKP reluctor wheel, CKP sensor and sent the heads out. That fixed the high speed miss but it deveoped a miss at idle on Cylinder 1...replaced the main injector and ran the GM cleaner through the fuel rail and poppets and the miss went away.

After a couple hundred miles of scanning and my scantool is pulling no misfires. I'm obviously glad it's fixed but I would've like to have know the root cause. I've got an appointment on Tuesday to change the tranny fluid and filter...and hoping that my CAT is not damaged by all the misfiring.

BTW...when I got it back I had the classic "partially engaged" 4WD, right front axle...loud whining and vibration at high speed that goes away when you hit the 4WD selector....replaced the vaccum switch on the transfer case (did the axle one as well) and problem solved. Upon inspection, both swutches have the ball stuck in the "In" position.


Thanks
Mike

[MT-2500]

Originally Posted by mdrush

Got my truck back from GM beginning of last week and she runs great. They replaced they ended up replacing the CAM shaft, CAM gear, Timing chain, CKP reluctor wheel, CKP sensor and sent the heads out. That fixed the high speed miss but it deveoped a miss at idle on Cylinder 1...replaced the main injector and ran the GM cleaner through the fuel rail and poppets and the miss went away.

After a couple hundred miles of scanning and my scantool is pulling no misfires. I'm obviously glad it's fixed but I would've like to have know the root cause. I've got an appointment on Tuesday to change the tranny fluid and filter...and hoping that my CAT is not damaged by all the misfiring.

BTW...when I got it back I had the classic "partially engaged" 4WD, right front axle...loud whining and vibration at high speed that goes away when you hit the 4WD selector....replaced the vaccum switch on the transfer case (did the axle one as well) and problem solved. Upon inspection, both swutches have the ball stuck in the "In" position.


Thanks
Mike

Thanks for posting back and letting us all know how it went.
Glad they got it fixed and give them credit for taking care of you.
Not all dealers would have do that good of a job.
But I am like you sure would be nice to have known the main problem.
Good luck with it.
MT