Utinator

Ok, I logged some data on the 2003 Surburban. See attached. I think the injectors are ok. The duty cycle seems low enough. I'm a little concerned with the fuel trims on the left side. It looks like the left side is running a little lean. I suspect there's a small vacuum leak on the left side somewhere. Can someone take a look and see if I'm on the right track?

PetZ

on idle there is only about 1-2% difference between B1 and B2 which is normal, but in the middle it is about 6-9% and in the upper range it is about 10% which is too much I think. It seems like a leak or bad O2. Try to switch the O2's if the results are the same.

Utinator

Ok, I just checked the volts on all 4 O2 Sensors. The Bank 1 sensor 2 and Bank 2 sensor 1 readings were almost off the chart. They were jumping around, but they stayed around .90 volts.

The Bank 1 sensor 1, and Bank 2 sensor 2 were reading around .45 volts. So it looks like those are ok.

I turned off the rear O2 sensors on both sides with HP Tuners. None of the MIL codes came on after turning off the rear O2 sensors. The engine was hot, so maybe that's why the engine light didn't come on....?

Another thing I noticed, was that the engine would not go into closed loop automatically. I had to command it into closed loop with the HP Tuners Scanner. Once I did that, it started trimming fuel again. When the weather clears up, my step-dad plans to swap the right side O2 sensors from front to back. I know that doesn't explain the lean indication on the left side, but that might clear the P0155 code for the right side.

cheep

Swap the FRONT O2 sensors from left to right and see if the fuel trims reverse.

Utinator

I just talked to my step-dad. He found the right front O2 sensor was unplugged. That would explain the bad readings and why it wouldn't go into closed loop. I'll scan it again the next time I am there.