need help with fuel pressure test

[dave1967]

I just tried to check fuel pressure but not sure what reading to use. When key is turned to run and fuel pump starts pressure is 50psi but after pump stops pressure holds at 38psi. Im tring to find out why 98 gtp starts but dies after a few seconds.

[troy1]

not sure for a GTP but my GT is about 42psi @ idle pull vac line off 50psi @ idle with engin off its 40psi & holds steady for about 5 mins GTP's should have more PSI than a GT.

Is your security light on?

[gprixgtp]

Ok this is out of the Motor Auto Repair Manual Service Pro edition
Fuel pressure is to be between 48-55psi. That is for the 98-99 3.5, 3800.
The 3.1 is 41-47psi.
Testing is as follows.
Loosen fuel filler cap to relieve vapor pressure.
With shop towel wrapped around fuel pressure valve to prevent fuel spillage, connect a suitable fuel pressure gauge to fuel pressure valve.
Check fuel pressure with ignition switch on, engine NOT running.

Hope that helps.

[BNaylor]

The L67 GTP has a two speed fuel pump via two relays in the engine compartment fuse box. There is a fuel pump relay and a hi-speed fuel pump relay. A common problem is the hi-speed relay not energizing due to a defective fuel pump resistor. Unless it is a security issue the symptom is the engine will die shortly after starting and may run only a few seconds. BTW - The GT and SE do not have a fuel pump resistor and hi-speed relay.

The proper way to check fuel pressure which will test both relay, flow from the fuel pump, fuel filter, lines and the fuel pressure regulator (FPR) is to connect a fuel pressure tester at the Schrader valve located on the FPR. With vacuum off the FPR proper pressure should read 48 - 55 psi. 52 psi is the median pressure for a GTP.

Initial fuel pressure is checked without the engine running (checks only fuel pump prime mode), however, full fuel system checks should be done with the engine running and disconnecting/connecting the vacuum line at the FPR.

Here's a procedure which is right out of the GM GP service manual which will check the fuel pressure regulator to rule it out:

Install fuel pressure gauge to Schrader valve on the FPR.

Remove vacuum hose from FPR.

Turn ignition to on (not start) and note fuel pressure reading on gauge.
Record reading.

Start engine and verify you feel vacuum at the hose end.

Reconnect vacuum hose to FPR.

Note fuel pressure reading again and record reading.

Now compare the first and second reading.

Fuel system pressure reading should be 4 -7 psi less with vaccum hose re-connected/installed. Fuel pressure should decrease as vacuum increases.

To rule out the fuel pump resistor checkout the procedure below:

http://rmcgp.clubgp.com/fpresistor.html

[dave1967]

Thanks for the advice. the security light is off so I've ruled out any security problems. I've replaced fuel pump, crank pos. sensor, checked and cleaned IAC, ran engine codes (none), and checked resistor with jumper wire. I've tried to check fuel pressure with engine running but it dies too soon to get a reading. I can keep the car running if I hold accelerator at rev limiter but then you can hear the fuel pump kick on and off. Is there an oil pressure shut off switch that could cause problem. Im running out of ideas

[BNaylor]

Originally Posted by dave1967

Thanks for the advice. the security light is off so I've ruled out any security problems. I've replaced fuel pump, crank pos. sensor, checked and cleaned IAC, ran engine codes (none), and checked resistor with jumper wire. I've tried to check fuel pressure with engine running but it dies too soon to get a reading. I can keep the car running if I hold accelerator at rev limiter but then you can hear the fuel pump kick on and off. Is there an oil pressure shut off switch that could cause problem. Im running out of ideas

To the best of my knowledge and reviewing the GP Vin 1 wiring diagrams there is nothing oil pressure switch related that could cause the problem. However, there is the engine oil level switch which the PCM monitors to shut down the engine. Switch is located on the side of the oil pan. It supplies either a ground or no ground to the PCM if oil level is low.

On theft deterrent although the SECURITY light is not on it could still be a TD problem. The body control module (BCM) and theft deterrent system sends a fuel system enable to the PCM. Normally if this is the problem you can at least get down the road for a few to several seconds before it shuts off.

Have you looked into the MAF sensor being a possibility? Just pull the electrical connector to the MAF and see what it does. At least you can rule it out. Is your PCM stock or re-programmed?

Whatever your problem is it is a doozie.

[dave1967]

I'll give the MAF a try and any ideas where the theft deterrent module is located? I'll post what i find out. Thanks

[BNaylor]

Originally Posted by dave1967

I'll give the MAF a try and any ideas where the theft deterrent module is located? I'll post what i find out. Thanks

If you have a theft deterrent module in your '98 GTP it should be located behind the right side of the instrument panel. However........:

Owning a GTP too I have never been able to find one. What I do know is the GTP has a Class 4 Body Control Module (BCM-4) meaning that all theft deterrent functions are integrated into it. In addition to all that there is a theft deterrent relay and a shock sensor relay. All these components are located on the left hand side of the dashboard. Just remove the kickpanel. The theft deterrent relay and BCM are located together in the tray that holds the BCM. The shock sensor is located next to those items but can be accessed through the panel at the left side of the dash. Fuel cutoff is generated by the BCM.

Hope the info helps and good luck!

[susanj]

Has anything worked for you yet? Having the same problem as you with my 97........it is driving me nuts........had at the dealer as a last resort and they had no clue........please let me know if you figure this out [email protected]. Thanks

[bbptech]

What fixed your problem? Son's 2000 GTP has same problem?

[BNaylor]

Originally Posted by bbptech

What fixed your problem? Son's 2000 GTP has same problem?

Sorry but please check the date and do not resurrect old threads. Best to start a new post explaining your current symptoms and what you have done to resolve the issue, if any action. In the meantime a common problem applicable only to the '97-'00 GTP is a bad fuel pump resistor where the fuel pump is not switching into the hi-speed mode. See link below located at our Tips & Maintenance forum.

http://www.automotiveforums.com/vbul...d.php?t=658282

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