Fuel Pump Not Prime

poppeman · #1 02-28-2009, 10:18 AM

I have a 99 GTP with about 175,000 miles on it. It's entire life the car will start right away with barely a turn over. A few weeks ago it would take a few turn overs to get it started. Oddly enough when i got a new tank of gas it started within the first turn over, so I attributed my problem with a bad tank of gas. Last night i went to start it and it was chugging and not really running. It almost sounded like not all the sparks were firing. Turned it off and tried again. Ever since I do not hear the fuel pump priming anymore. It will not start, just turns over. The fuel pump is not starting.

What are my first steps; the cheapest ones? If the pump is not even turning on, could it be the relays or fuses? I have not checked anything yet. What is common in this car? Or is it most likely that the whole pump went bad?

Any help would be appreciated. I am ready work on anything this weekend.

BNaylor · #2 02-28-2009, 10:23 AM

Obviously check the fuel pump fuses and the fuel pump and fuel pump speed control relays at the engine compartment fuse box. Then check fuel pressure at the front fuel rail. 48-55 psi. BTW - The two relays are interchangeable.

poppeman · #3 02-28-2009, 12:14 PM

I checked the fuses and i also swapped the relays, i did not purchase new ones but just interchanged them. I also unhooked the battery and checked the connections on the fuel pump itself. I unhooked them and rehooked them, everything seems to be correct.

I do not know how to check the pressure. Do i need something special to check it?

So far nothing seems to be fixing the problem.

BNaylor · #4 02-28-2009, 12:29 PM

Come to think of it since you do not have fuel pump prime checking fuel pressure would be moot at this point in time. At that electrical connector at the fuel pump assembly you can check for the 12 volts and ground needed for the fuel pump to work. Also, check for 12 volts at the fuel pump fuse socket even though the fuel pump fuse looks good. The fuel pump relays are controlled by the PCM module. The PCM applies a ground/low to the relay to energize and there is 12 volts at the other side of each relay coil at ignition to ON.

Also, there is a fuel pump test electrical connector located below the engine compartment fuse box at the wiring harness. You can directly apply 12 volts and a ground at that connector. Just be sure to use a fused wire jumper, 15 amps for the 12 volt source. Use any good chassis ground for the ground. When that is done you should be able to hear the fuel pump. It bypasses all the other circuits just for troubleshooting test purposes.

If you do not detect any fuel pump activity when this test is done then the fuel pump is suspect.

poppeman · #5 02-28-2009, 12:53 PM

I get 12V at the fuse for the fuel pump that is in the fuse compartment in the engine. I tried to test the connection at the fuel pump itself in the trunk and I only get 5V. There are two connectors on the fuel pump. One is a 4 wire and the other is a 3 wire. The three wire one is where i can get 5V off of the yellow wire with a stripe and either of the other 2 wires.

I looked below the engine fuse box and see a green/yellow wire connector. Is this what you are calling fuel pump test connector? If I unhook this and apply 12V fused I should get the pump to run if it is still good?

Thanks

BNaylor · #6 02-28-2009, 01:47 PM

The right connector at the top of the fuel pump assembly is the one with the most wires shared with the fuel level sending unit. The other connector is for the tank pressure sensor used only for evaporative emissions. See pic. Top connector.

When you use the test connector the fuel pump should start working if not then it is bad or maybe a short/open in the wiring.

poppeman · #7 02-28-2009, 02:14 PM

I am still only getting 5V on the correct connector at the fuel pump. I unplug it and turn on the ignition and that is all i get, 5V.

I am not sure if the disconnect connector under the fuse panel with the yellow/green wires is the correct one, i dont want to unplug it and apply 12V to it if its not the correct thing. What else can i try.

BNaylor · #8 02-28-2009, 02:17 PM

Just to clarify.

On the 4 wire electrical connector at the fuel pump assembly the two contacts for the fuel pump motor are the following:

Pin B - Gray Wire - 12 volts
Pin C - Black Wire - Ground

Pins A (purple) and D (black/white) are for the level sending unit only.

Note: The test connector is a pigtail so it should not be connected to anything.

poppeman · #9 02-28-2009, 03:04 PM

Alright, I was finally able to prove that on the B & C connectors at the fuel pump I am getting 12V for a second or two when I turn on the ignition. I hooked it back up and do not hear the pump turning on like i normally would. I would assume that since i am getting 12V there would be no need to give it a straight bypassed 12V, correct? The 12V it is getting for a couple of seconds would be enough to turn it on. I tried giving it a "Whapp" like i read in other posts, still nothing.

What would my next step be? Is there anything else that could cause it to not even prime. Would the fuel filter have anything to do with this symptom?

Whats next?

Thanks

BNaylor · #10 02-28-2009, 03:15 PM

The PCM module controls fuel pump prime for the two seconds. The fuel pump is forced in to high speed mode at that time. If you get the 12 volts there for the 2 seconds then that is enough and shows the circuits are working properly and that includes PCM module control.

IMO your fuel pump is bad.

I did not think hammer modulation aka beating on it would work like some morons we get have suggested.

poppeman · #11 02-28-2009, 03:29 PM

I was pretty sure the hammer modulation would not work either, let's call it I decided to hit it with a hammer out of frustration and then noticed it still did not work.

I checked local shops and found that one of the auto stores sells fuel pump assembly for $252. Does this sound reasonable. The other stores were $311 and $291.

Any key advice when I start to replace the pump that would save me time and frustration?

Thanks

BNaylor · #12 02-28-2009, 03:34 PM

You're welcome.

The price is reasonable for an aftermarket. The Delco units are higher unless you get lucky. Visit our Tips & Maintenance subforum for additional information on fuel pump assembly replacement. See link.

Click here

Good luck and let us know how it turns out.

poppeman · #13 02-28-2009, 03:39 PM

Also, I noticed that my tank is half full right now. Is it mission critical that i have less than a quarter of a tank? Since I can't even get the car started it is hard for me to run the gas down. I would almost have to siphon the gas out and can't even think of an easy way to do that. Am I just going to have a mess if I do it with a half of tank of gas?

BNaylor · #14 02-28-2009, 03:47 PM

Just go for it. Half tank will be OK. Just have plenty of old rags draped around the opening in the trunk area to catch any dripping off and soak up any excess gas. It will be there even with 1/4 tank since the pump assembly housing holds it. After pulling the pump assembly straight up and out do not tilt it. Also, just be sure to adhere to good safety practices. Battery negative cable disconnected, etc.

poppeman · #15 03-01-2009, 02:18 PM

Well I did the work this morning and had not hitches at all. I thought the snap ring was going to be rusted on, but a couple of taps freed it right up. I used the o-ring that was with the original pump, when I tried to get the new one down it just wasn't going. The old o-ring still looked in excellent shape and slid in a lot easier. I put it all back together, no leaks, no problems now.

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