Lean codes. MAF codes wont go away. P0171/P0174/P0102

JC1188 · February 8, 2020

I have a 2004 suburban. I didn't see a pre 2015 topic so I chose silverado being they're basically the same. Anyways I have the LM7 5.3. 95K miles. When I bought it, it was throwing P0171/P0174 system too lean. I put on a new MAF, intake gasket, fuel pump, pcv line. Sprayed carb cleaner all over anything I thought was leaking and couldn't notice anything. Cleaned the k&n air filter and did not oil it. Nothing made the code go away. Put a second MAF on, delphi brand. Cel went away for a while but evap monitor would never complete and P0171/P0174 codes were still there. Ignored it for some time.

Now cel comes on and will not go away under a new code of P0102. I cleaned the MAF, cleaned the throttle body and cleaned the air filter again. Nothing. Cel comes right back on with P0102.

Haven't checked anything with an ohm meter yet but the wiring and connectors look good. Any thoughts or help would be greatly appreciated.

davester · February 8, 2020

Are all the exhaust manifold bolts still there and tight? And the bolts clamping the manifolds to the exhaust downpipes?

As for the P0102...didn't read your post close enough... Actually check the wiring harness to ensure it has good connectivity and doesn't have a short,

JC1188 · February 12, 2020

I figured out the problem and fixed the p0102 code. Loose wiring on the maf connector. But unfortunately now I'm back to the P0171/P0174 codes.

CamGTP · February 12, 2020

Smoke the engine to find leaks from the intake and the exhaust. Anything before the o2 sensor will come up as a lean issue.

Other possible cause is fuel pressure. You will need to get a fuel pressure gauge and hook it up to the fuel rail. See what your key on engine off pressure is. See how fast is bleeds back, see what your idle fuel pressure is and what the running fuel pressure is while driving.

The computers injector data is based off of a base pressure of ~58psi, so if the fuel pressure you are seeing is only 45-50psi, then it will read lean because not enough pressure is behind the injector.