Weird Fuel Pressure Issues

[Austen Leach]

Hi I have a 2004 Tahoe with a 5.3 flex fuel engine. It has a small cam, long tubes, and a cold air intake.

The issue that I’m having is that at idle my fuel pressure is only showing about 42-44psi with my regulator plugged in and only about 52psi with the regulator unplugged. I’ve already replaced the fuel pump with a stock unit and the fuel filter was replaced with a Wix at the same time as the pump. I’m getting rich fuel trims and setting lean codes for both banks. Does anyone have any ideas on what could be happening? Bad fuel pressure regulator?

 

[91RS]

Sounds normal. Should be 48 or higher with the engine OFF after the pump primes.

 

[Fless]

Sounds normal. Should be 48 or higher with the engine OFF after the pump primes.

The spec for NBS Flex is 48-54 psi, with (as @91RS states) KOEO (key on, engine off). Make sure the intake is solid and not leaking any unmetered air after the MAF, and clean the MAF with -- you guess it -- MAF cleaner. Could be a vacuum leak, O2 sensor. Any exhaust leaks?

 

[Austen Leach]

The spec for NBS Flex is 48-54 psi, with (as @91RS states) KOEO (key on, engine off). Make sure the intake is solid and not leaking any unmetered air after the MAF, and clean the MAF with -- you guess it -- MAF cleaner. Could be a vacuum leak, O2 sensor. Any exhaust leaks?

I replaced the MAF with a brand new Delphi unit. I’ve smoked both the exhaust and intake to check for leaks and can’t find any. Both upstream O2s are swapping pretty consistently from .1v to .9v without any weird spots on the graph

 

[Austen Leach]

Sounds normal. Should be 48 or higher with the engine OFF after the pump primes.

Could my tuner have possibly set me tune up to try and get 58 psi out of it and the computer is trying to compensate?