XPSII800HO

I have a 2002 GT(5 speed), it has not been running right for a couple weeks. I have changed the plugs, it still felt like it had a miss. You notice it most when idling down with your foot off the gas at 1800 rpm and again at 1000 rpm(it's worse at 1000) I had the car on a scope at a dealer and it showed random misfires on all cylinders, changed the plugs again and it got a little better for a few days. I cleaned the air filter, cleaned the MAF and IAC, and changed the fuel filter and nothing helped. I had the IAC gasket mod on the car and have put it back to stock.
Today I borrowed a scan tool, there is no codes showing on the car. But watching the scanner with the car running showed fuel pressure from 35 - 39 psi at start up, if you let it idle for 10 minutes it would climb to 65 psi, as soon as you start driving it goes back down to 35-38 psi. The car shows no misfires on the scanner, but it would it just be real weak on the cylinders not getting enough fuel? What should the fuel pressure be?

cliffyk

The '03 shop manual says 50 psi KOEO (Key On Engine Off), 43 psi at hot idle, 39 psi at 30 and 50 MPH w/ a steady load.

These are all "typical" values that may vary by as much as ±20%...

The slow rise to 65 psi at idle is troubling, I have no idea what might cause it except some overheating of the pressure sensor or some other fuel line related component.

Have you tried disconnecting the battery for 5-7 minutes to clear the KAM (Keep Alive Memory)? That's where all learned values like idle air, and fuel trims are stored, resetting it is always a good idea after mucking about with intake components.

XPSII800HO

Yeah I disconnected the battery when I cleaned the MAF and IAC. I reset everything again yesterday with the scan tool. There is a little round chrome thing in the fuel line, a diaphragm or something. It seems to be getting pretty hot, not sure if that is normal.

Silver01StangGT

The little round chrome thing in the fuel line is a fuel pressure regulator to the best of my knowledge. I have been told by the dealer at one time, those are not made anymore and the dealer does not stock them. Not sure if that means it is not necessary or not. Mine is still installed. Maybe someone else who knows more about that part will add to the thread about it, and if it is necessary.

cliffyk

I think it's a pulse dampener to keep pressure pulses from the injector's opening and closing from the messing up the Fuel Rail Pressure (FRP) sensor's readings.

The electronic returnless system doesn't have a classic mechanical pressure regulator as the PCM uses the FRP's output to control the duty cycle of the signal to the fuel pump driver module. The FPDM then controls the speed of the fuel pump so as to maintain the target pressure.

It gets hot from engine heat, but should not be any hotter than general under hood temps--which are pretty damned hot, 220°+

The odd part is that I cannot find it in any of the fuel system sections of the '03/'04 factory shop manual? Maybe it was found to not be needed and that's why it's no longer available...

SSFenris

sounds like the problem I'm having... subscribing.