2012 Tahoe 5.3 with Misfire on 4 ...

[Ivanhoe]

Hello,

I have turned to this forum for ideas as I’m losing patience with my Tahoe. I have a 2012 5.3 Tahoe with 225,000kms. It has rough idle, the stabiltrack and traction side orders and misfire on cylinder 4. A friend mechanic has pulled the head to check the AFM lifters and cam - all seem fine. Plugs changed, coils and leads all ok. I believe injectors were checked as well. Looking for ideas of where to check next ? Code reader gave up p0300 random multiple misfire then p0304 cylinder 4 misfire.
New engine/ dealer repair price is beyond my means .
Any ideas ?
Thanks

 

[wjburken]

How did they check the coils? Did they swap them and get the problem to move or did they stay?

Might be your coil harness.

 

[Ivanhoe]

How did they check the coils? Did they swap them and get the problem to move or did they stay?

Might be your coil harness.

Not sure as I was away working at the time. The mechanic is usually very thorough and very experienced, the work was done for a favour so I didn’t want to question his work too much. I changed the coils and cables myself as well and no change. I cleaned MAF sensor and after attaching battery again the faults cleared for about 10 minutes then returned

 

[iamdub]

The problem could be in the VLOM, which wouldn't be visible. Clear the codes and drive with it in manual mode in gear 4. This will keep AFM from engaging. If all is well, shift into "D" and see if the misfires come back as soon as it tries to go into V4 mode.

 

[Ivanhoe]

I have a range afm disabler on it now to prevent the afm kicking in

 

[BG1988]

I have a range afm disabler on it now to prevent the afm kicking in

did you make sure it has enough oil low oil can cause misfire as well

 

[malvizar]

When I had this issue with my 07 Tahoe, it was a collapsed lifter due to oil starvation. I had to get an AFM delete kit and that revised valve cover for oil consumption. Runs on all 8 cylinders now at all times like it should’ve to begin with. Runs great now. Good luck

 

[iamdub]

I have a range afm disabler on it now to prevent the afm kicking in

Well, shit. Your problems may be more serious. No ticking or anything when it's misfiring? Maybe it is injector or spark after all.

 

[wjburken]

I really think it’s worth while to check the harness going to the coils.

 

[wsteele]

The multiple misfire code might be telling you something about a general condition that exhibits itself most often in number 4 due to tolerance stacking and/or maybe two separate issues.

Does your mechanic friend (or you) have access to a scan tool where he/you might look at misfire counts, watch the numbers in real time, check O2 sensors, fuel trim, etc?

Although a long shot given the inspections that have already been performed, I probably would do a quick and dirty compression check on 4 as well.