Sounds like a bad MAF..... Be willing to bet swapping em fixes it!!!

 

Hope its the MAF that would an easy fix,

I'll swap it this afternoon and see

Neal

 

Could try cleaning it too but ive seen that play hell with an already f'd up MAF, seems to do more harm than good...

 

Well pulled the Denali MAF and put it in the silverado and the same issues with the random misfires and cold cranking so back to the drawing board.

I sprayed the intake and everything around it with starting fluid while watching the fuel trims and nothing changes. The only vacuum line I didn't restrict was the evap purge line so thats next on my list to cap off and see if that may be the issue. I have another set of injectors that i can put on but I really don't think this is the issue as the misfires are random not specific to any one cylinder. I'm going to do a cylinder balance test to see if maybe I have an issue with a particular cylinder but this also wouldn't cause random misfires on all cylinders.

I'm going to do some more comparing the PID's with the Denali to see if anything looks out of the ordinary other than the low MAF sensor readings.

Neal

 

sub'd

 

did some more trouble shooting,

pulled the brake booster vacuum line to make sure the booster was not the problem, nothing there.

Pulled the evap purge solenoid and plugged the hole to verify that wasn't the issue, it wasn't.

the one thing i notice about unplugging the MAF is that the IAT is located in the MAF as when I disconnect the MAF the air temp drops to -31*.

Still looking over the PID's and comparing them to the Denali

Going to swap the fuel injectors as soon as I have time since I have another set sitting there.

If that don't do it I'll be pulling the intake to verify I don't have a leak.

Neal

 

Found some testing software within my scanner software so plan on doing a few tests to see what I can find out.

We ended up changing the upstream O2 sensors as one failed while we were trouble shooting last week. The wave forms look better than the old sensors but the misfires are still there.

I found a little test procedure that I'm going to do to check the fuel injectors. The test procedure is called an injector balance test. I can turn off each injector 1 at a time with my scanner software and watch the fuel trims to see how much the trim compensates to get the AFR back to 14.7. By comparing the fuel trim percentage of compensation per injector turned off it should tell me if there is an issue with the injectors.

Next I plan to do a VE test and see if there is something there that is out of spec.

I'll post back and give an update once I get the testing done.

 

Post the original 4.8 tune, and the modified tune you are using.

 

I'll check with the guy that changed the tunes for me and see if he can get them to me.

The tune right now is the GM factory tune for a 02 2500 with a 6.0l and the original tune was the GM factory 99 4.8 tune.

 

What year was the Engine out of???