Misfire at Idle and Slight Acceleration No DTC's

[Duce57]

I own a 2007 GMC Yukon Denali with the L92 6.2. It currently has 203,000 miles on the clock and I am kind of stumped. I have a misfire at idle and slight acceleration with no codes. I have replaced all Spark Plugs with AC Delco Iridium Plugs, AC Delco Spark Plug Wires, and all AC Delco Ignition Coils but the misfire is still there. I as trying to track it down by looking at a scan tool but the misfire seems to move cylinders. I also replaced the negative battery cable due to it being in really rough condition thinking that could be a cause.

- I even have an issue with an extended crank when the vehicle sits in for awhile in warm weather. I figured the VVT Oil Control Valve sticking and causing the issue but after replacing the Cam Sensor, VVT Solenoid, VVT Oil Control Valve, and Timing Chain and Sprocket, the issue is still there too.

 

[j91z28d1]

sometimes extended crank after sitting a while can be fuel pressure bleed down and has to build back up, takes a little while longer to fire up.

can be injector leaking or fuel pump check valve. could check fuel pressure, and if that look good have the injectors cleaned?

 

[Fless]

Look up a Crankshaft Position Variation Relearn, and have it done. Just to rule it out.

 

[solli5pack]

The fact that the misfire jumps to different cylinders is interesting. You able to view misfire history with a scanner to see if any cylinder was missing more than others? Or maybe isolate a bank.

 

[Duce57]

The fact that the misfire jumps to different cylinders is interesting. You able to view misfire history with a scanner to see if any cylinder was missing more than others? Or maybe isolate a bank.

I found some time to take it for a few test drives and it seems like the misfire occurs most often on cylinder 4. But it seems like it is intermittent. I know that exhaust manifold leaks can sometimes cause a misfire but all but a couple bolts are broken on it and I don't think that would be the cause of a seemingly intermittent misfire.

 

[solli5pack]

My Yukon has a only at idle misfire on 5 and I hear either lose lifters, exhaust leak or cat rattle on that side. I've been so tied up with working on my Suburban I haven't had a chance to figure it out. It's on my list of things to do. I saw a cool trick on a you tube video where some dude hooked his shop vac up blowing into the tail pipe and sprayed soapy solution all around the exhaust connections. You see bubbles you found a leak. If you have exhaust leaks it probably good to fix them first and then troubleshoot the misfire. They need to be fixed anyway.

 

[solli5pack]

Just did the shop-vac trick on the Yukon. Cyl 7 & 5 got bubbles like a mofo at the exh manifold. I really hope when I fix that it clears my misfire.