Re: Code P0174 &P0171 65 miles after LS Swap installed.
What I do is....Scan the PCM for High LTFT & STFT readings (Lean) with he engine running, If they are high +15 or higher.......Unpin the Yellow wire from the MAF, Start the engine (It will set a P0101) & monitor the Long & Short Fuel Trims, If the fall back to Zero +/- 5....Suspect a faulty/dirty MAF OR the MAF in the wrong/bad location, My Camaro set lean codes using a stock tune truck PCM because where the MAF is located about 6 inches forward of the throttle body. A custom Tune fixed mine, If the same is true for you....Relocate the MAF closer to the stock Truck location.
If unpinning the Yellow wire has no effect on LTFT/STFT in closed loop, Suspect a Vacuum Leak.
Running open exhaust will also cause a Lean reading by the O2 sensors.
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