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No power getting to fuel pump, please help


SlowGSX
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Hey all.

I am new to this platform

but not to cars in general. I recently bought a 98 Regal GSX. It has a few mods

but nothing extreme. Last night on the way home it just stopped running. No

sputtering or anything, it was running fine then just suddenly cut off. It will

crank but not fire. The fuel pump wasn't priming so I pulled it out and tested

it directly off the battery, it still works fine. Which it should since its an

AEM pump that's less then three months old. Anyway, I checked all the fuses and

replaced both the relays, one labeled fuel pump and the other labeled fuel pump

speed control. That didn't help so I broke out the voltmeter. I have power at

the fuse block both at the fuse and at the input to the relay, but its not

making it all the way back to the pump. I even tried jumping the relay connector

pins 87 and 30 which if I'm reading the wiring diagram correctly should have

provided power to the pump but I still get none.

 

I am at a loss here.

The only other thing I can think of is maybe the factory security system is

interfering? Any other ideas/suggestions? Please help, this car is my only

transportation at the moment. Thanks.

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Broken/corroded wire between relay and pump??? Do you have voltage on the pump power wire at the harness connector closest to the pump? (Should be nearly battery voltage when fuel pump relay is activated or jumped.)

 

Broken/corroded wire between pump and ground??? Do you have voltage on the pump ground wire at the harness connector closest to the pump? (Should be less than 1 volt, because that wire is grounded.)

 

Wire harness problems inside the tank are epidemic.

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I do not have voltage at the pump connector.

Work backwards from there to where there IS voltage.

 

Do you have voltage at the #30 terminal of the relay socket? I don't have a wiring diagram for your vehicle, but If you jump 30 to 87, yeah, I'd expect the pump to run.

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I have power at terminal #87 of the relay socket. According to the diagram I was looking at, 87 is power in and when the relay is active, 30 is power out to the pump. But when I jumped 87 and 30 I didn't have power at the connector. So the loss is presumably somewhere between the power out from the relay and the pump connector.

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you could have a bad oil pressure sensor my sensor went out in my car but instead of it killing the fuel pump it made it stay on all the time even when the car was off

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Does the fuel power circuit go through the oil pressure sensor after the relay on this? The diagram I looked at made it look like after the relay it went straight back to the pump.

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Does the harness that runs to the fuel pump for power/ground actually run through the tank?? I didn't want to have to drop the gas tank to look for an open circuit.

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The ground at the connector is good. I did a continuity check between the power wire at the connector and terminal #30 of the relay socket and there is no continuity. So that power circuit between #30 and the connector is where the failure is. I think instead of dropping the tank and ripping the harness apart, I'm just going to run a new power wire with a toggle switch and a relay and use the power from the fuel pump fuse to trigger the relay. It'll run a little rich at idle and low load but that's fine, the car needs to be retuned anyway. This will be alot easier then tracing the break in the harness I think.

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you could have a bad oil pressure sensor my sensor went out in my car but instead of it killing the fuel pump it made it stay on all the time even when the car was off

1. I think his car is new enough that GM may have done away with the oil pressure bypass.

2. The oil pressure switch can't turn the pump "off" if the ECM has activated the fuel pump relay, and the FPR and wiring is in good condition.

Doesn’t the 98 supercharged Regal have a fuel pump resistor like the 98 Grand Prix?

I'd love to see that schematic.

The ground at the connector is good. I did a continuity check between the power wire at the connector and terminal #30 of the relay socket and there is no continuity. So that power circuit between #30 and the connector is where the failure is.

This is the connector closest to the fuel tank?

 

I think instead of dropping the tank

Why would you drop the tank when you know the problem is in the harness ahead of that connector?

 

I'm just going to run a new power wire with a toggle switch and a relay and use the power from the fuel pump fuse to trigger the relay. It'll run a little rich at idle and low load but that's fine, the car needs to be retuned anyway. This will be alot easier then tracing the break in the harness I think.

The way my '92 and '93 are wired, the fuel pump fuse is hot all the time. The ECM turns the relay on to activate the fuel pump when desired. You can't use the fuse to trigger another relay, the pump will have power all the time.

 

Why would that make the engine run rich?

 

 

 

You don't want to trace down the real problem? Route a new wire from the existing fuel pump relay socket (#30) to the proper cavity of the connector you've been testing from. Fixed, and with no change to pump operation.

 

 

 

 

 

 

 

To my way of doing things, you need to look at the schematic for your vehicle to see what else in involved with the fuel pump power circuit.

Edited by Schurkey
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It is the connector closest to the tank. As far as dropping the tank, I hadn't actually looked at the routing of the wiring and my friend said I'd have to drop the tank to access part of it so I took him at his word. I hadn't actually checked to see if the fuel pump fuse was hot all the time or not, I just figured if it was I would trigger the relay with a toggle switch. Or do it how you said and run a new wire as a direct replacement for the broken one, I feel stupid that doing that didn't occur to me. I thought these cars decreased fuel pump voltage at low load and idle, so I assumed running a constant 12v to the pump would mean it would run rich at idle unless the PCM could dial the injectors down enough to compensate.

 

According to the wiring diagram I looked at, there is nothing else between #30 power out from the relay and the connector at the pump, the wire runs straight back. Which tells me the problem is a break in the wire itself, right? Call me lazy but I don't think its worth the time to trace the break when running a new wire is much faster and easier.

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