2002 2500hd Fuel Pressure Question

[ChrisJ914]

Working on a 2002 2500hd 6.0L that was having some hard starting problems. Would turn on the key, pump would come on, and the motor would turn over, but wouldnt start at first. Turn off the key, try again, starts right up. Replaced the fuel filter (up until 03 still have the in-line filter) and it seems to start right up no problem now. Still wanted to check pressures just to be sure though.

Connected my pressure gauge to the test valve on the fuel rail. When the ignition turns on and the pump primes it comes up to about 55psi like its supposed to, but then drops right back down. Still starts, and at idle sits at 49 psi, which in my research seems to be just fine. If I disconnect the vacuum line on the pressure regulator, the pressure jumps up about 8psi, just like it is supposed to.

The question I have, is why does the pressure drop off right after the pump and ignition come on? Is it supposed to do that? I thought I read that it was supposed to come up and stay, but could have read it wrong.

Thanks

[txab]

Check valve on the pump is probably bad

[8.1HD/ALLISON]

+1

 

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