2001 Suburban 5.3 Parts Cannon Victim Running LEAN

My new-to-me '01 Suburban 5.3 (129k miles) has p0171 and p0174 and occasionally p0300 misfire codes.  Truck's history was that it has been in NC its entire life, but sat for 12 years and was sold to PO who wore out the parts cannon, replacing injectors (N115B 25317628, 46/psi), MAF, PCM (used), wires, plugs, coils, EGR valve, fuel pump, fuel filter, o2 sensors, etc.  IDK if the truck has a tune or a cam. 

Truck starts fine when cold but when hot often has a long crank before starting and surging.  Truck runs and idles fine otherwise but does have some pinging I can hear. 

I found the original intake manifold was warped and replaced it with a Dorman.  I also replaced the cheapo O2 sensors with Denso (up) and GM (downstream).  Bank 2 downstream O2 shows about 1/6th to 1/10th the voltage of bank 1 downstream, which makes me think there might be a clogged cat on that side.

Vacuum leaks at EGR tube gasket, oil dipstick tube and throttle body have been eliminated. A small leak on the throttle shaft seal remains.

MAF shows 6.39 g/s at idle, MAP at idle shows 37 kPa, (local baro is 100 kPa).

Fuel pressure at the Schrader valve was 48 psi at idle and 52 psi under load with vacuum applied to the FPR, 54 psi without vacuum to the FPR which remained consistent at idle and under load.

LTFT at idle are 25% on both banks.  STFT are usually positive as well.  Misfires have gone down a bunch since replacing the O2 sensors but there are still a few.  They were found mostly in the front two and rear two cylinders.

I'm at my wit's end trying to figure out why it's running so lean. Any ideas for next diagnostic steps welcome!

How do your fuel trims behave when you raise the engine speed up to 2,500 RPM with the engine warmed up? Better or worse?

If you watch Engine Load on the scan tool and run WOT through first and into second, what's the highest value you see?

LT Fuel trims do not fall off above idle or under load. LT FTs vary between ~17% and 25%, with bank 2 generally a bit below bank 1.

With your fuel trims being significantly lean at idle and under load, I tend to suspect a fuel delivery issue. Vacuum leak is unlikely, and your reading of 6.3 g/s at idle doesn't suggest an air measurement issue. Doing the Engine Load test like I described above would definitely help to prove or disprove an air measurement concern.

I see there's a used PCM in it. Do you know if the PCM was programmed to the vehicle after replacement? You could start with pulling the VIN out of the PCM and see if it matches that of the vehicle.

 

Thanks, I'll check the PCM. I checked the plugs on bank 1 and they were all close to white, very light coffee color. NGK brand fwiw. I am currently diagnosing a no crank no start condition that presented after I replaced the plugs.

I checked the fuel trims at WOT under load and they did not go down. STs went up a bit, LTs stayed high (25% B1, 17%B2).
PCM Vin matches the truck.

When checking compression, I found that two Bank 1 spark plugs had cracked ceramic. Replacing them has eliminated the misfires and caused Bank 2 LTFT to drop to 5%, Bank 1 LTFT to drop to 12-15%. No more CEL. I consider that a win at this stage.