GTP fuel pump resistor problem...

[gtp4life]

I bought a 98 grand prix GTP 3800 supercharged. Since I have bought it, I have replaced many parts. The other day I started having problems with the fuel pump not running, I changed the relays for the fuel pump, and the car would start and run for about 2 seconds then die. When I unplug the MAF, it will run for about 15-20 seconds, then die. I have looked around on the internet, and everything pointed to the fuel pump resistor.

I bought a fuel pump resistor today, and went to put the resistor in, and the guy that owned it before me didnt even have the resistor hooked up! He had a wire connecting the two prongs of the connector that are supposed to go to the resistor. I plugged in the resistor already on the car and it ran like crap, engine rocked like crazy then it died, put the new resistor on, same thing, and tried it with no resistor, same thing. I now hooked it back up the way he had it with the wire and have the 85 prong on the relay bend out like you would to bypass the resistor and it runs fine now, you can just smell that its running really rich

My questions are, why will it not run right with the resistor in there now, and why did it never do this before and just happen all of a sudden? HELP!!!!!!!!!!!!!!!!!!

[3100]

Resistor decreases voltage to pump to slow down pump motor and reduce pressure. Check the voltage at the fuel pump connector with ignition key to on position you should see battery voltage for about 2 seconds, so tell someone to turn the key to the ON position for you while you are checking for voltage. Be careful under the car.

Also tell someone to hit the gas tank with a rubber mallet while you are cranking see if it starts. If yes pump could be ready for new one.

[tblake]

Will the car run if you plug the resistor in and bend the tab out on the relay.

[gtp4life]

How would that work? Bending the tab out on the relay bypasses the resistor to be able to test and make sure it is what is bad an not the pump itself...so if the tab was bent it wouldnt matter if the resistor was there or not, it is bypassed all together..

[tblake]

Originally Posted by gtp4life

How would that work? Bending the tab out on the relay bypasses the resistor to be able to test and make sure it is what is bad an not the pump itself...so if the tab was bent it wouldnt matter if the resistor was there or not, it is bypassed all together..

Yeah but you are missing my point. You said the first owner bypassed the resistor all together by unplugging it and inserting with a jumper wire in its connector.

If you plug the good resistor in, the car should run regardless with the 85 tab bent out, only the pump should run in high speed mode. This would test the fuel pump system wiring. If the pump wont even run with the resistor plugged in and 85 bent out, you have issues elsewhere.

I suspect whoever you bought it from had the fuel pump go out, so they replaced it with the wrong one (maybe a single speed pump from a GT or SE or 01+ GTP) and in order to get it to run they jumpered the resistor's connector as a half @$$'d repair. Now your having issues. Maybe with a bad pump, or with the shoddy 'repair' job from the previous owner. Who knows.

I will see if I can track down a wiring diagram.

Just my

[BNaylor]

Makes sense to me Tim. Good reply.

The bottom line is what does the fuel pressure read at the front fuel rail using a standard automotive fuel pressure testing gauge? '98 L67 engine fuel pressure should read around 48-55 psi at fuel pump prime (ignition to ON only).

[old_master]

The schematic shows two relays and the resistor. One relay is the fuel pump relay, and the other is the fuel pump speed control relay. They are not interchangeable.

PM me with your email address and I can attach the PDF and send it to you.

[BNaylor]

Originally Posted by old_master

They are not interchangeable.

Sorry but I disagree. The fuel pump relay is the one right above the fuel pump speed control relay shown in the pic below. Same part numbers, therefore, interchangeable.

[old_master]

Ahhh, could very well be. In the schematic it shows the coil being wired differently... probably for illustration purposes. I stand corrected, thanks.

[richtazz]

I agree that first you need to check fuel pressure, but both at prime and while running at idle. If the pump is borderline, it may run while in high-speed mode (which is also used in key-on prime) but not i low speed mode. The higher current supplied in high speed mode may be enough to keep it running, but in low-speed mode, the weak pump fails. I agree with Tim that the resistor/relay/jumper wire mess up front was a prior owner/mechanic's half-a$$ed attempt at a repair.

[gtp4life]

Yeah the fuel pump is definetly bad...The car wouldnt start again today and the fuel pump wouldn't prime at all untill I smacked the tank with a rubber mallet then it fired over. As far as the resistor mess goes I'm not sure if the one I have now is bad or not. I guess once I get another fuel pump I will be able to tell It just sux they cost around 280 bucks ohhh well.

[gtp4life]

Ok, replaced the fuel pump and the car will not run without the fuel pump resisitor bypass STILL! I got a new resistor and put it in with a new relay and the car just went crazy...idle was all over the place then it made an ungodly scrape kind of sound for a few seconds and died. Started it again, idled fine for about a minute then did the same thing..so..its back to bypassing the resistor again...any ideas? I am starting to point toward PCM or fuel pressure regulator...?? HELP! lol

[BNaylor]

Since you are not the original owner(s) I wonder if the fuel pump re-wire mod was applied? Could be a component or wiring shorted. Using a wiring diagram I'd check out the wiring looking for shorts or opens. The PCM module energizes the fuel pump relay by applying a low so that can be checked out before replacing the PCM module.

Have you checked voltage at the fuel pump electrical connector with a multimeter to see what voltage is present?


Unless properly troubleshot all you will be doing is throwing parts at it and wasting money like in the case of replacing the fuel pump.