02 Silvy 5.3 p0171 headscratcher

[gmchevroletruck]

Hello all. Having a rough time finding an issue, was hoping an actual expert could chime in...

2002 Silverado 5.3 LM7 built in Canada.

Symptoms: p0171 code, left bank lean. No driveability or idle issues whatsoever.

 

Replaced: Intake manifold gaskets, front 02 sensors (different part # for Canada models), checked / replaced vacuum hoses under the hood.

Cleaned MAF sensor.

 

Notes: 1) CEL illuminated consistently, with the following exception. Once in a great while, after refueling, the CEL will go off, stay off for maybe a few miles and return.

2) In hotter weather, upon removing the fuel filler cap if the tank is very low on fuel, a very very very long and very powerful air release occurs at the filler cap upon removal. Not sure if this is related. Fuel cap has been replaced.

 

Anyone care to chime in? Yes, I know the dealer can fix it...haha

[txab]

Check fuel filter, fuel pressure and injectors. Also check for any exhaust leaks between the engine and O2 sensor

[Wiggy McCrackin]

I just had the exact same as issue. For me it was cleaning out the mass air flow sensor. Be sure to plug it in when you're done too or it will shift hard. Ask me how I know. Could be an o2 sensor. If you're not getting enough fuel pressure, you might have to replace a fuel pump. I think anything below 50 psi means that you're not getting enough fuel pressure. But I would double check that to be sure. There are YouTube videos on how to test your fuel pressure. And you can rent a fuel pressure contraption at autozone. Do you have trouble starting it when its really cold out?