[dmarty]

I learned a little more today. I replaced the O2’s and as expected, the problem remains. I was able to use the PC to record the problem, but with my inexperience with the software, only recorded about two thirds of what I should have. I found that for a period of about 4.8 seconds when the popping and backfiring (sounds like a string of firecrackers going off under hood) was going on, the short term trim on 1&2 went to 0.0 and the long term on 1&2 went to 9.36 and the O2 trim on 1&2 went to 0.0 and all held constant for the full 4.8 seconds. Normally was getting 0.0 to -4% ST and -1.5 to +1.5 LT and 0.0 to +4% O2. I should have recorded RPM and throttle position, but failed to.

The new O2’s have a nice pattern and healthy cross count and the downstream O2’s have a nice flat line if I let things settle down for a few seconds after moving the throttle.

It did set a code today. P0336 for the crank sensor, but I thinking it’s a result of the backfiring and may have jerked the crank around enough to set the code. I was stupid and erased the code without checking to see if the PC could read a snapshot of it. Hope I can set another one tomorrow.

Had to quit today as the truck warmed up and would not repeat the problem and the PC battery went dead. It was so warm today, that the truck never really cooled off. I’ll try again in the morning with cold engine and charged PC battery.

I did notice the PC read an ECM test report and it said something about the EGR failed the test. Still no codes though other than the crank position. I tried to repeat the test, but it wouldn’t do it and erased the data. Maybe the engine has to run for a longer time? I’ll try again tomorrow.

Found a thread on another site today where someone with a similar problem found that it was weak exhaust valve springs on 3 and 5. Hope that’s not it. I’m still thinking it’s bad injectors or bad EGR.

Any thoughts? Thanks!