What else could cause low fuel pressure?

[Grand Prix SD]

I have a 2000 GT that seems to have low fuel pressure. I replaced the original fuel pump because the car wouldn't stay running. It had about 42 psi fuel pressure. Turns out it was the MAF that caused the problem. I replaced the original pump with a bosch unit and the pressure was still low. So i took it back to the autoparts store and got a new one. Same thing. My car is stumbling like crazy when i floor it so their must be a major problem. I have replaced the fuel filter and the regulator and neither helped. I am going to check the pressure on my 99 to make sure the pressure gauge is good. If that's not the problem i am out of ideas. Hopefully one of you have the answer.

[BNaylor]

How many miles do you have?

42 is on the low side but that depends on how fuel pressure is tested. What brand fuel pressure tester gauge are you using? What are the readings at fuel pump prime - ignition to ON not start? And what is the reading with the vacuum line disconnected and plugged that goes to the fuel pressure regulator?

[Grand Prix SD]

It has 135,000 miles. I used a novia equus tester. I just rechecked the pressure and it is 47 psi with the key on, 42 psi engine running, and 52 psi with the vacuum line disconnected/plugged. Maybe the pump needed time to break in? I do have the original ignition wires on this car but new rapidfire plugs. By the way, i checked my 99 GT and it has 42 psi key on, 42 psi running, and 52 psi vacuum line disconnected/plugged. So maybe fuel is not my problem?

[BNaylor]

I agree. Fuel supply looks good. AC Delco Rapidfire 14 plugs??? Although they can be used but not a good replacement spark plug for the OE AC Delco 41-921. Ceramic has been known to crack so check that out. IMO best one to use for stock is the AC Delco 41-101 Iridium or the NGK TR55IX Iridium.

Also, your ignition wires sound suspect due to the mileage.

[Grand Prix SD]

I replaced the wires since i already had them and it turns out one of the contacts on the coil was completely covered in rust. So it was either that or the wires that were bad because now all the stumbling is gone. My only other problem now is my car seems to restart too fast when it's hot. I turn on the ignition and it seems to start the second it cranks. It wouldn't really be a problem except that it seems to idle low for a bit like it's in drive then kicks up. You can just tell it's not right. I'm thinking maybe the injectors are leaking into the manifold?