Random misfire - 8.1 104,000 miles

[wakecumberland]

I purchased a 2006 Suburban with the 8.1 about 2 months ago and it is throwing a random misfire code periodically. I get the flashing check enigine light any time I am unloaded and exceed aprox 65 mph and it usually occurs on the downside of a hill or rise. I also get the light around 50 mph when I am towing something. I do not sense a misfire and the truck seems to drive fine with no noticeable difference in engine revs or power before/during/after the light.

 

I have just changed the sprak plugs and wires and that did not solve the issue. I also tested the fuel pressure and it checked out. Where do I go next? Could it be an O2 sensor or something similar?

[Jsdirt]

That code sends me into an angry frenzy ....

 

Not familiar with that particular engine at all, but on the 4.3 V6 that problem could be related to intake gaskets or the injection spider. No spider on that engine that I know of, so could be an injector issue, fuel pressure issue, ignition issue, vacuum leak, or intake gasket leak.

[ATMINF]

It might be the crank position sensor, on the 8.1 L engines they have had some issues with that sensor. It has caused some headaches.

[Z45]

Perform a crankshaft sensor variation relearn.

 

I know of 3 people with 2500 and this same problem. Each had the problem go away after doing this. One fella spent a lot of $$ replacing parts to no avail and it took a lot of persuasion to convince mechanics it could be this.

Sooooo, I went by my buddies shop yesterday and had a discussion about the misfire problem. He used his diagnostic scanner to relearn the cps. Took a whole two minutes. I then hit the hwy, cruised at 80 and no flashy da CEL! I went about 15 miles with no issue (knock on wood).

[wakecumberland]

Thanks! I'll try the CVS relearn and report back.

[wakecumberland]

Well the relearn did not fix the problem. The check engine light went away for a couple days but now its back to its old tricks again. Any other thoughts?

[yukon25008.1]

check the coil packs.. go thru the carwash and see if it starts missing I had that issue, Also watch the rear drivers side manifold bolt for exhaust leaking.

[wakecumberland]

Car wash causes no problems. I would expect some specific cylinder misfires if it was a coil pack issue. How could I know whaich coil pack is bad?

 

How can I check to see if i have an exhaust manifold leak?