Fuel Pump won't kick on?

[Wildone]

I am reaching the ends of my knowledge here guys. My fuel pump will not kick on when I attempt to start of the car. I have an aftermarket fuel pump, a hotwire kit, and a new fuel filter, I had the fuel pump installed about a year ago. I have checked the fuel pump fuse, the relay on the passenger side of the car, the relay on the hotwire kit. I have hotwired the pump to see if it is bad and it kicked on for me, so I know it is working. I have replaced the computer thinking the ecm may be bad and not sending a signal to kick on the fuel pump. Is it possible one of the grounds are bad in that area? Any help would be appreciated.

John Wilde

 

[UNGN]

There is a fuel pump relay that has to be working to have the fuel pump cycle when you turn the key to "on".

If the FP relay is bad, the Oil pressure switch will provide power to the circuit, once oil pressure has reached a certain level.

 

[Steve Wood]

John,

Why don't you start at the factory fuel pump relay on the passenger fender?

It should have four wires on it.

1. Pink/black wire from the fuse block-should be hot when the key is in the Run position.

2. Dark Green wire which comes from the ecm. It should be hot for about two seconds when you first turn the key on.

3. Gray wire.....this goes to the fuel pump. It becomes tan/white at a connector in the rear of the car. It should be hot for the same two seconds when the key is first turned on.

4. Black/white wire.....goes to ground. It should read ground all the time.


Assuming you have been checking the right relay, before you test the individual wires above, take the fuel pump test lead behind the alternator and connect it with a jumper to the battery stud on the back of the alternator. The fuel pump test lead is connected to the same gray wire going to the rear of the car. If the pump runs, I think the problem has to be in the original circuit under the hood and not the hotwire kit.

If it does not run, then I think we have to look at the hotwire side.

 

[Datsunboy]

Steve, I troubleshot it for john. As best i could without a schematic anyway.

Hotwire is working fine, If i jumper with a test light the pump kicks on.

He has no current to the hotwire to trigger it. I didnt think there was a relay in the car for it.

John, sounds like ill be back out to the Wilde compound sometime LOL. We can try swapping relays out of my GN, but I have school stuff till friday. Let me know if i can help.

Later man - Evan

 

[Wildone]

Thanks guys, I will try this out this evening.

John

 

[Steve Wood]

I think most of the commercial hotwire kits retain the factory relay and use the tan wire at the rear of the car that originally powered the pump to now trigger the hotwire relay.

Therefore, if the factory relay fails with age, the hotwire quits working....however, if the factory oil pressure sender is still intact, power should be restored after enuf cranking has incurred to build 4# of oil pressure.

It's a jury rigged setup, in my opinion, but it makes it easy to "plug and play".

 

[Wildone]

Steve,
Is it possible the ground it the fuel pump is bad? How would I
check this. As Evan stated he was able to get the fuel pump to kick on, but I am not sure how he did it ( I was the key on/off man). My neighbor has checked both relays at work, and says they are both good. What else could be causing it?

John

 

[Steve Wood]

Kinda doubt that the ground is bad...otherwise it would not have run when he put power to it.

Go back to my first post and check the wiring out. Start with supplying power to the fuel pump test lead under the hood.

If the pump does not run, go to the rear and check the tan/white wire for power at the original tank connector plug (be sure the fuel pump test lead is still connected to 12 volts when you check at the rear.

 

[Datsunboy]

John, i was able to engergize the hotwire kit with they key on OR off. I basically took constant power from the wire that runs to the battery (thick, red) and tapped into that, then plugged it into the wire that activates your fuel pump (tan wire?). This popped on the fuel pump, so that leads me to belive there is something wrong in the stock wiring. If you cant trace it down, let me know. I think its either the oil pressure switch, or the relay under the hood. Im still a bit unfamiliar with the factory wiring, but know for sure that the hotwire is good. I read the schematic for the fuel system on www.gnttype.org I really reccomend you check it out. Its in PDF form and very easy to read and understand (If i had it at the time i would have identified the relay under the hood immediately).

Did you say you had a larger turbo sitting waiting to go onto your engine? I thought you had. I plan on some clever plumbing with the new air intake, so if you are interested in selling the factory unit let me know.

BTW, the wheels do look much better without nasty rusty lugnuts! Thanks again man.

Later bud - Evan

 

[Steve Wood]

The oil pressure sending unit has nothing to do with it unless the wiring harness shorts out and pops the fp/inj fuse. This happens sometimes when the the sending unit is discarded when using an aftermarket gauge and the connector is left dangling.

 

[Wildone]

Datsunboy,

Last night I bypassed the hotwire kit, and still the pump would not kick on. You checked all the fused none of them were blown, correct? I had my neighbor test my fuel pump relay today, and it works. So I have elminated, the fuel pump fuse, the factory relay and the hotwire relay. You jumped the pump, so we know it is working. What else is there, other than a bad ground? Thanks again. As you stated, there is constant power going to the tank, as you were able to kick over the pump that way. Did you use the contstant power from the stock power lines or the hotwire lines? Thanks again

John

 

[y-hate]

Just had that problem, i rehook my hotwire kit to the intank pump and the pump did not come on, it only work with the stock wire. I also heard the hotwire kit relay kick on, but still did not work, so luckly i had a spare relay the same as the hot wire kit and just replaced it...then like WHOA the intank pump was humming louder than ever....so just replace the hotwire relay, just a thought

 

[Datsunboy]

Alright bud, I got the constant power from the wire that was run for the hotwire kit. I dont THINK you have a bad ground or I would not have been able to trigger your fuel pump manually.

You are correct in that I did test all of your fuses in the fusebox. Hell, its so easy with a test light why not?

GUYS here is what we have it narrowed down from;

Hotwire Kit is functioning properly.
No power at the factory fuel pump wire.
Relay under the hood is good for the fuel pump
ECU has been swapped, hoping that would help.
I triggered the fuel pump by jumpering past the factory wire and applying power to the hotwire, pump fired right up.

I am NOT sure whats going on here folks? Help john out! I need to hear his hooker catback system

John, your ground has to be solid because I was able to power up your fuel pump by applying power to the relay trigger.

I also attempted to bypass the hotwire when I was at your house and got nothing (like you did).

My question is how the oil pressure switch works. Why is it there and whats its purpose and hows it do it? If I remember correctly that is the sender that tells the car to not run the fuel pump with no oil pressure right? Maybe its bad and broken (making the car think theres no oil pressure when there is).

John, you had some serious undervoltage going on there. How did the battery take to the charger? I am still thinking that might be a problem.

I also unhooked the ECU, and plugged it back in. When i turned the key on, it built fuel pressure and shut off. When i went to start it didnt do squat, i got like nothing for pressure. Thats why im thinking hes undervolting his warlboro 370 pump. His voltage was dropping (the day i was there) down to like 7 volts during cranking. I dont think thats enough to keep the fuel pump pushing fuel when attempting startup.

Any ideas guys?

Evan

 

[Steve Wood]

think I gave you the procedure for checking out the wiring up above

 

[Racetronix]

Steve is right! You can sit and hypothesize all day about this problem but until you go through the proper diagnostic procedure step by step without missing a beat you will not be able to find the problem. You could quite easily have a defective factory harness / connection

I will scan and post the GM diagnostic flow chart later today as this will help find your problem.

Jack
Racetronix

 

[Datsunboy]

Turns out john had a fuel pump cutoff switch that somebody bumped. Thats right isnt it john?

The reason I was hypothesizing was because I live about 40 minutes from john and wanted to go armed with as much knowledge as possible.

THANKS ALL - Evan