HELP!! Strange issue

[Blkdoutbird]

Hey guys I recently ran across a vehicle with a strange issue that I can't seem to get figured out. The vehicle in question is a 2007 Avalanche that has a small Crane cam and longtubes. The stft and lftft are reading max lean 25+ after the startup enrichment ends and the vehicle goes into closed loop. It gets so rich the engine begins to bog down and wants to die due to the excess fuel. When I put it into open loop it clears up and idles normally. The O2's have been tested and work normally, the MAF and MAP are reading correctly, a smoke machine has been put on the manifold to check for intake leaks, there are no exhaust leaks, cam timing has been verified. I keep circling back to it being an electrical or ground issue from what I'm seeing. Have any of you ever ran across or experienced this before? I'm sorry for not having a datalog of what's going on and I am currently away from the vehicle.

[blindsquirrel]

I have seen something similar. At the dealership there was a brand spanking new HHR that tripped a P0171 after lot-idling.

All the data looked perfectly normal, except at idle the trims would slowly drift and max out and set the code. No leaks anywhere. Reset trims, let it idle for 5 minutes, code comes back. Clear it, reset trims, go drive it for hours and hours and NO codes. Stop and let it idle, CEL again.

Changed O2, no difference. Swapped MAF/airbox lid with another new HHR, no more codes. I eventually found a tiny little piece of plastic airbox swarf lodged against one of the bars in the MAF. It was in just the right place that it would skew things at very low airflow volumes, above idle it was a small enough effect that the ECM could compensate for it.

[Blkdoutbird]

Thanks, I'll try that next.

[5FDP]

I've seen the virtual alcohol sensor cause weird fuel trim issues. It will report 30-50% ethanol content even though the tank is E10 at the most.