Hey SD community, my name is T.J., and I've got a weird fuel control operation, just curious if anyone else has seen this/can provide some insight into what I'm experiencing. So this is an 08 Suburban with the 5.3 that came in with CEL, intermittent misfire, and intermittent low power on the freeway. Vehicle has 260,000 miles. I've already diagnosed as O2 faults; vehicle needs genuine OE O2S, but I'm not sure if it will also need a PCM due to what is happening with the decel fuel cut operation.
Codes were:
P0054 HO2S heater resistance B1S2
P0134 HO2S circuit insufficient activity B1S1
P0152 HO2S circuit high voltage B2S1
P0161 HO2S heater performance B2S2
P0171 Fuel trim system lean B1
P0175 Fuel trim system rich B2
P0300 Random misfire
P0430 Catalyst system low efficiency B2
P1174 Fuel trim cylinder balance B1
P1175 Fuel trim cylinder balance B2
Customer has had a different shop install new plugs, has had B1S1, B1S2, and B2S1 O2 sensors replaced 3 times, and I believe the fuel filter as well trying to fix this truck. Plugs are Bosch and are gapped correctly, but I will be recommending installing AC Delco plugs as part of the repair procedure because I'm not a big fan of using Bosch parts in newer GM engine control systems. The 3 O2s that were replaced are no name sensors, and the B2S2 is an original AC Delco. So that this post isn't a full novel, I wont detail my diag process unless it becomes needed info. The B2S1 O2 would stick over a volt @ cruise on the freeway and the PCM would pull the B2 STFT negative 22% to negative 25% on that bank, but the LT would never adjust, just stayed @ 0%. Sensor voltage would drop lean, below 100 mv under 3/4 to WOT throttle, and ST would climb positive quickly, but still no B2 LT adjustment. Now this is where I first noticed this oddity; I accelerated from freeway cruising speed under that 3/4 - WO throttle to around 4,500 RPM, but when I let off to trigger decel fuel cut, the computer would never cut injection. Inj PW would show 1.9ms on both banks and the B1S1, B1S2, and B2S2 would show activity as though there was still closed loop control occurring, and the B2S1 would return to over 1 volt, but still no fuel cut. So, I hope that's enough preliminary info to help answer my question of why this vehicle won't ever command fuel cut during full decel from high RPM conditions, and why the B2 LT value would never compensate. That LT adjustment may prove to be a non-issue once the correct O2s are installed, but the failure to cut injection is concerning to me as far as the PCM's fuel control operation goes. Any ideas are welcome with open arms, because I don't want to overlook a potential issue with the PCM in addition to the O2s. I can provide any further pertinent info/test results as needed. Thank you all, look forward to hearing any and all input!
Travis T.J. Harrison
Foreman @ Kelley Automotive
Sacramento, CA
Topic Author
