P0171 & P0174, Fuel Pump?

[bowtiegurl]

07 Yukon 5.3 Engine started to bog down and die when coming to a stop, then it would restart and shift hard upon acceleration. Service stabilitrack came on then the CEL. Pulled codes P0171 and P0174. Checked fuel pressure it was 52psi with key on, when started it went to 50psi then dropped to 40psi with acceleration. Does this mean it's the fuel pump causing the codes? Fuel pump was replaced not even a year ago so it's still under warranty. Don't want to pull pump again if there's something else that could cause the low fuel pressure.
I should add that the LTFT go as high as +32%. Also I disconnected the MAF sensor plug and it would not start with it unplugged.
TYIA

 

[Foggy]

07 Yukon 5.3 Engine started to bog down and die when coming to a stop, then it would restart and shift hard upon acceleration. Service stabilitrack came on then the CEL. Pulled codes P0171 and P0174. Checked fuel pressure it was 52psi with key on, when started it went to 50psi then dropped to 40psi with acceleration. Does this mean it's the fuel pump causing the codes? Fuel pump was replaced not even a year ago so it's still under warranty. Don't want to pull pump again if there's something else that could cause the low fuel pressure.
I should add that the LTFT go as high as +32%.
TYIA

Usually those codes are vacuum leak oriented
40 psi is lower than it should be.. does it stay at 40 \??? or go back up some
when you let up some on the throttle??
And how are you monitoring the fuel pressure ?

 

[bowtiegurl]

Usually those codes are vacuum leak oriented
40 psi is lower than it should be.. does it stay at 40 \??? or go back up some
when you let up some on the throttle??
And how are you monitoring the fuel pressure ?

Fuel pressure gauge connected to the Schrader valve. Fuel pressure started dropping lower than 40 when I let off the gas pedal. The warmer the engine gets the more symptoms I have it starts running like crap.

 

[Foggy]

Fuel pressure gauge connected to the Schrader valve. Fuel pressure started dropping lower than 40 when I let off the gas pedal. The warmer the engine gets the more symptoms I have it starts running like crap.

Good deal with a mech gauge. Sounds like a fuel pump for sure

 

[Fless]

Diagnostic path for fuel pressure (verify that I selected your vehicle, or navigate to the similar page for yours):

Fuel System Diagnosis — 2007 GMC Yukon 4WD V8-5.3L Service Manual | Operation CHARM

Detailed repair manual for the 2007 GMC Yukon 4WD V8-5.3L.

charm.li