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No Fuel Pressure

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derekstl

New member
Hey Guys,

Brand new to the forum here, looking for some advice. I have a 07 GP with the 3.8L V6 and 191k miles. It had an issue overheating and I flushed the coolant and replaced the thermostat, but no luck. Took it to a shop and they suspected the head gasket went bad. Long story short, I did the work myself, tore it down to the block, found several coolant passages completely blocked up, (will have to share pictures of that later) and put everything back together. Having some issues with it starting now. It will crank just fine but with kind of sputter but never actually start. I thought it was a timing issue and checked the basics, then replaced the camshaft sensor as it got really wet with some coolant and thought it was malfunctioning. Still doing the same after so I rented a fuel pressure gauge from AutoZone and tonight realized I have no fuel pressure after hooking up to the fuel rail. (i checked it on my other car and the gauge read correctly) So now I am looking for some advice on what to do next. When I turn the key I do not hear the fuel pump, but dont want to just jump into replacing it, instead want to identify the root cause. I tried to look at fuses and relays and everything looked normal, not sure how I should proceed from here. Any advice???
 


It's most likely the pump.

You will need to check voltage at the connector above the fuel tank to make sure the signal is getting there.
 
Thanks for the reply. Do I just need to turn the key on and then use a test light on the wire to see if it has voltage? Or if I need to use a voltmeter what should the reading be?

I just think its so strange when you have random things like this where the fuel pump randomly goes out when I am doing something completely unrelated . . .
 
I didnt have the time to work on the car tonight, but poked my head under the car while it was still on the ground. Am I even able to access the connector above the fuel tank without dropping the tank itself? Didnt seem like I could see or get to the connector at all.
 
pull the carpet out the trunk and the back seat, theres a trap door you can ope up. like 8 nuts. pumps right under it and the plugs.
 
You most likely won't have the trap door in the trunk on your car. It's worth the time to check though.

If it's not there, you'll have to drop the tank.
 


Scottydoggs said:
pull the carpet out the trunk and the back seat, theres a trap door you can ope up. like 8 nuts. pumps right under it and the plugs.
Click to expand...

Yeah I checked, I dont have the access panel. I think they stopped that in the 04 model and mine is an 07. No idea why they would stop, I wish they didnt, but unfortunately they did. I am considering just cutting a trap door to access it and then silicone sealing it back in after. I know its not ideal but reality is that its a 12 yr old vehicle with close to 200k miles and the car really isnt worth anything if its not running . . . would be nice to make it a much quicker and easier process if I have the trap door.
 
they saved a ton of costs having one less big hole to punch and a total of 8 or 9 extra parts that didn't need to be put on the car removing that door that's why they did it. whoever thought of the idea probably got a nice raise lol but screwed over anybody servicing the pump in the future. I would probably do the same as you and just cut a trap door but just be warned there is less than an inch of clearance even in the good spots where the hoses and connecters are even less so id be extra careful doing the cutting having a power shear would be optimal but I know most people don't have this tool
 
Yeah I have a sheet metal "nibbler" that I can use, only goes like 1/4 inch under the surface so I should be good. Would still like a little advice, once I cut the trap door and have access to the pump and wires, how can I verify the pump is currently getting power? Is there a way to jump the wires and see if the pump kicks on? Want to make sure I am fixing the issue before replacing the pump.
 
Test light or digital multimeter. If it has power and won't run, as a hail Mary you can reverse polarity and see if it will run just for a couple seconds. Sometimes the impeller can get stuck by debris and this will free it.
 


Ok. So I cut an access panel for the fuel pump and replaced it . . . It still will not prime. I have taken my test light to the fuel pump relay and can verify it's got power there. The other fuses are fine. I also took the test light to all 4 wires in the connector to the fuel pump but cant get a live read on any of them. This is strange because if I leave the key to the ignition in the ON position and unhook the fuel pump connector the fuel gauge goes down and the low fuel indicator beeps. When I plug it back in it goes back up. This tells me that the purple wire does indeed have power, I have switched the ground of the test light to about 10 different locations but still dont get a read. Long story short, I still cant verify that the fuel pump is getting power or not.

I have kept the fuel pressure gauge hooked up the whole time but can never get fit to budge from 0, not even when cranking the car. Another wrinkle to it, I sprayed lots of starting fluid into the intake manifold and tried to start the car but didnt get any different results. (The car cranks just fine but never really acts like it might start) Theoretically if all I was missing was fuel then it should start for at least a second. Maybe something else is wrong??

Can anyone help me please?!?
 
Sounds to me like you have a bad wire or connection someplace. I would try to power the pump directly from the battery to confirm the new pump is good.
 
GTPpower said:
Sounds to me like you have a bad wire or connection someplace. I would try to power the pump directly from the battery to confirm the new pump is good.
Click to expand...

How exactly do I power it directly from the battery? Any idea where other connections are? Not sure what connections to check.
 
You don't have power to the pump. Hook up any 12v you can to test the pump. If that means taking out the pump and taking it to a battery, or taking the battery to the pump is your call. You said there was 12v to the relay. How did you test that? Under the fuse block? You need 12v on pin 30. Pin 87 will always be powered. I'd swap in a new relay first. I've never had one go out but you never know. If the relay is confirmed good, and pump turns on when jumpered to 12v, then you might have a break in the power wire somewhere. Quick fix is to install a fuel pump wire upgrade.
 
bandook said:
You don't have power to the pump. Hook up any 12v you can to test the pump. If that means taking out the pump and taking it to a battery, or taking the battery to the pump is your call. You said there was 12v to the relay. How did you test that? Under the fuse block? You need 12v on pin 30. Pin 87 will always be powered. I'd swap in a new relay first. I've never had one go out but you never know. If the relay is confirmed good, and pump turns on when jumpered to 12v, then you might have a break in the power wire somewhere. Quick fix is to install a fuel pump wire upgrade.
Click to expand...

You were right, no power to the pump. I hooked it up to the battery directly and it kicked on. I have swapped out the relay multiple times and it didnt help.

When I tested the fuse block I had power on one of the pins. (I just used a basic test light with a ground, doesnt measure voltage or anything) When you are looking at the 4 slots it was the top right one. I dont know which one is pin 30 or 87 and couldnt find any diagram that would show me.

I traced the wires from where it connects to the fuel pump and I found a connector under the car near the rear passenger tire. I tried my test light on all the pins from the connector and didnt get anything. So I am not getting power back there. That connector goes into the trunk and you see the wires run under the back seat. Didnt notice any cuts or anything that would cause a problem.

How would the power wire go bad? I did just replace a blown head gasket so I have been in the engine bay a lot. Is there a link to the fuel pump wire upgrade tutorial or products to buy? Trying to do this cheap so I can sell the car.
 


Fuel Pump Rewire Kit – ZZPerformance

The pins on the relays are labeled on the underside. But you said you've tried new relays so I doubt that's your issue. Maybe check continuity on the pump ground wire. This rewire kit would be the surest bet IMO. Or you could trace the wire and figure out where you lose power. Remember to seal any area of the wire you probe with liquid electrical tape, nail polish or whatever. Or you'll have the issue again. Good luck man, pixie demons are the worst.
 
bandook said:
Fuel Pump Rewire Kit – ZZPerformance

The pins on the relays are labeled on the underside. But you said you've tried new relays so I doubt that's your issue. Maybe check continuity on the pump ground wire. This rewire kit would be the surest bet IMO. Or you could trace the wire and figure out where you lose power. Remember to seal any area of the wire you probe with liquid electrical tape, nail polish or whatever. Or you'll have the issue again. Good luck man, pixie demons are the worst.
Click to expand...

Thanks again for the info and help, really appreciate it. So today I uncovered the wire where it goes to the connector in the trunk and it does not have any power. I took the back of the fuse panel off to get a better look at the wires coming in and believe that I located the same gray wire. With the key on, I dont have any power to that wire directly out of the fuse box. I took a quick video for reference to help explain. My thought now is that maybe the computer is not sending signal to power the pump??? How the F do I fix that???

07 Grand Prix no power to fuel pump - YouTube
 
I couldn't tell if that was tested with key on. Also, I had the pins backwards. Pin 30, the one you had power on, is straight to battery basically. With key on you should have 12v at pin 87. Look at the bottom of the relay. Pin 85 will be what switches the relay on, closing the circuit between 30 and 87. 86 is your ground. I'm no electrician for sure but this shouldn't be that complicated.

Basically you can't get power to the pump without the relay in and key on.
 
My bad, the video was misleading. I checked the power to the wire with the key on and relay plugged in. But your right, when I took the video I took it.
 
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