testing fuel pressure on 04 grand prix and hard starting when hot

I have been having problems starting my car after its hot and sits for 20 Min's approx, I have to press the gas peddle to get it to start and turn it over lots

what i have done so far is:

1. changed fuel filter
2. checked spark while the symptom is happening and with spark plug wire tester and it showed spark
3. cleaned throttle body tore it apart
4. cleaned MAF sensor it reads (g/s) 4.92 on obd2 (not sure if that is goo still learning about this)
5. checked codes with obd2 scanner
6. codes showed up as
7. p0455 - p0128 i have a ect just have to change it my reading is 89 de C
8. changed antifreeze (to prep for winter)

What I get when I hook up my fuel pressure gauge and the car is running is 57-58 psi but when I turn my key off it drops to 0 right away is this normal?

When I turn on the key without starting the car I can hear the pump priming but the gauge reads 0 psi till I turn it over quite a bit then the pressure climbs up to 57 psi and starts right away (again is this normal or is it not priming right? )

i would say you need a new pump/sending unit.... when it primes you should be getting fuel pressure

That's what I was thinking new pump sending unit but its weird that it only does it when the car is hot . is there a reason for this ?

i'm still trying to figure out the fuel system on this its the first time i ever seen one with out a return line at the motor and just a return at the filter does anybody have a good explanation for this because my service manual is not helping me at all !!!

Its a returnless fuel system.

Seems that tons of people are having issues with these cars hard starting after they are hot.

Originally Posted by skinner

That's what I was thinking new pump sending unit but its weird that it only does it when the car is hot . is there a reason for this ?

i'm still trying to figure out the fuel system on this its the first time i ever seen one with out a return line at the motor and just a return at the filter does anybody have a good explanation for this because my service manual is not helping me at all !!!

i would check the fuel pressure regulator for leakage.