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Fuel Pump Wiring Double Checking having issue

Old 03-02-2015, 10:46 PM
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Default Fuel Pump Wiring Double Checking having issue

Hello, I am having an issue with the sending unit wire in my 95 teg gsr. Blk/White ground wire keeps melting to being live some how... Please let me know if I did this wiring correctly for the relay.

Factory Blk/White (large) Fuel Pump wire is grounded to rear of car... does not go to relay on 85. I have 85 going to kill switch then ground of chassis.

*Edit: 2nd diagram at bottom is the revised one, final outcome
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Last edited by ESP.net; 03-15-2015 at 03:11 PM.
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Old 03-03-2015, 06:50 AM
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Default Re: Fuel Pump Wiring Double Checking having issue

The fuel pump should be grounded with as short of a ground wire as possible not all the way up to the thermo housing. I never use the small black relays for a high load situation either. Use a 100amp battery isolator relay. They're inexpensive and work flawlessly. I had issues melting wires on the black relays with a walbro 450 previously.
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Old 03-03-2015, 07:18 AM
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Default Re: Fuel Pump Wiring Double Checking having issue

Thanks for the post.
I dont believe the bosch relay will be an issue. The ground ran to thermostat is best possible ground for unibody? Alternator post has a breaker 30 amp type fuse. Fuel pump works...prime hums right etc. Nothing is getting warm but the single blk/white sending unit wire which is melting. As in my other thread.
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Old 03-03-2015, 08:56 PM
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Default Re: Fuel Pump Wiring Double Checking having issue

Not smart to have a kill switch to turn off just the pump. That's asking for lean conditions.

Also, you need to upgrade the ground. It should match the power in awg size.
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Old 03-04-2015, 06:16 AM
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Default Re: Fuel Pump Wiring Double Checking having issue

Cluster film or repin harness...?

Last edited by 89turboaccord; 03-04-2015 at 06:55 AM.
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Old 03-04-2015, 07:19 AM
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Default Re: Fuel Pump Wiring Double Checking having issue

Tepid... fuel pump ground goes directly to thermostat in 10 gauge. Trigger wires 85 n 86 are both small wire like 16. Where would you put the kill switch ground seems like a better option then positive trigger 86
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Old 03-04-2015, 10:47 AM
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Default Re: Fuel Pump Wiring Double Checking having issue

Originally Posted by ESP.net View Post
Tepid... fuel pump ground goes directly to thermostat in 10 gauge. Trigger wires 85 n 86 are both small wire like 16. Where would you put the kill switch ground seems like a better option then positive trigger 86
Kill the ECU, not the pump.
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Old 03-04-2015, 11:20 AM
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Default Re: Fuel Pump Wiring Double Checking having issue

I see what your saying but regardless this should not effect any of the issue I am having with the Fuel Sending Unit blk/white wire frying in my other post
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Old 03-05-2015, 01:49 PM
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Default Re: Fuel Pump Wiring Double Checking having issue

What is your reason for grounding this at the thermostat? You're adding quite a bit of length for absolutely no reason. You mentioned/asked if the thermostat housing was the best ground for a unibody? That's what battery negative is for.
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Old 03-05-2015, 03:22 PM
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Default Re: Fuel Pump Wiring Double Checking having issue

the body is metal, not plastic. Do you have anything tapped into the sending unit ground? There are multiple ground locations on the car besides the thermo housing. anything at or less than 5 ohms on the ground side is acceptable. It doesn't have to be .1 ohm. Besides, it's all about voltage drop, not continuity.
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Old 03-05-2015, 03:59 PM
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Default Re: Fuel Pump Wiring Double Checking having issue

I have since taken out the Kill Swith on the negative. Wired up the stock larger blk/white negative wire to the relay 85.

For trouble shooting sake and melting wires... I have grounded the blk/white small fuel sending unit wire to the chassis in the cargo area with an inline fuse. Been using 10 and 15 fuses still blowing them now upon ignition. The Blue/White wire is getting 11.8 volts when grounded with voltmeter. The Yellow/White is getting 7.1 volts when grounded with the voltmeter...

I then took the relay out to turn the pump off... turn ignition on and no blown fuses with all wires hooked up.... The pump is causing it to fry and heat up the ground for the sending unit???? I am going to take the Fuel Pump out tom. and double check.

I used the thermostat housing thinking it would be the best ground. I will go ahead and extend the wire to the battery negative.
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Old 03-05-2015, 05:09 PM
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Default Re: Fuel Pump Wiring Double Checking having issue

I have since ran the negative off the thermostat to negative on battery. No change.
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Old 03-05-2015, 05:29 PM
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Default Re: Fuel Pump Wiring Double Checking having issue

I am thinking I have narrowed the culprit down. I will know more in the morning...

The below post is a guy with the exact same problem:

Fuel sending unit phantom power. | DSMtuners

Maybe the pump is causing a short in the tank? As shown above maybe wasnt a good idea to use that screw clamp to make sure it would stay in and zip ties might of been a better option...
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Old 03-06-2015, 12:39 AM
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Default Re: Fuel Pump Wiring Double Checking having issue

Before taking the pump out. Disconnect the power wire going to the pump after the relay (don't ground it). If wire still burns fries whatever then you know it isn't the pump and it's in the relay or wiring.

if you unplugged the relay to turn off the pump and it didn't fry the wiring then that leaves more than one option for your problem is why I'm suggesting this. This sounds like it's been a huge headache for you and hopefully gets figured out.
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Old 03-07-2015, 09:59 AM
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Default Re: Fuel Pump Wiring Double Checking having issue

Yes it has been a big pain in the neck on the better part of 3 days... I am no electrical wizz so took twice as long... I knew wasn't going to be easy...

Fuel Pump was indeed grounding out on the top hat. Negative stud was shortenin through the thin rubber grommet.... used my other fuel pump hanger took out n de-pinned 20 gauge wire n pinned up 10 gauge.... problem fixed...i am keeping my inline fuse on the ground blk/white sending unit wire just incase...
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Old 03-07-2015, 11:16 AM
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Default Re: Fuel Pump Wiring Double Checking having issue

Glad it got sorted out man.
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Old 03-10-2015, 08:16 AM
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Default Re: Fuel Pump Wiring Double Checking having issue

Good job. Yes electrical is and can be really difficult. Especially when brain ******* yourself. Melted wires are created by excessive load or short. I still wouldn't run the fuel pump ground all the way up front.
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Old 03-10-2015, 02:14 PM
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Default Re: Fuel Pump Wiring Double Checking having issue

If I had to do this again... I probably would of but the ground to chassis in the cargo area. Wires already ran and I don't think it will hurt a bit to negative battery terminal. I read somewhere about having the negative and positive being carried the same length also is better... I wont even try to get into the science of it lol... So from alternator post back and negative battery back is how I have it now...
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Old 03-11-2015, 04:10 PM
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Default Re: Fuel Pump Wiring Double Checking having issue

science smience...lol (maybe for car stereo). you want the ground to be shorter so there is less voltage drop. It should be alright, shrugs shoulders, Just another way to make the pump work harder. And your right, learn from mistakes and apply it on the next one. Don't take me for a dick. internets show no emotion.
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Old 03-13-2015, 08:51 AM
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Default Re: Fuel Pump Wiring Double Checking having issue

The Aero 340 and Walbro 255 have current draws of less than 15amps. Unless he runs wire more than 20 feet, he could use 12 gauge copper wiring for both power and ground, and ground it anywhere in the car with proper contacts to sheet metal.
The 14g ground does need to be upgraded.
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Old 03-15-2015, 02:54 PM
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Default Re: Fuel Pump Wiring Double Checking having issue

Far as I know 85 and 86 trigger wires can be small. Although they are 14/16 gauge from stock 18 gauge or so fuel pump + and -.

All hot wire in and out to pump are 10 gauge. Blk negative from pump to negative post on battery 10 gauge as well.

Yes you are correct you probably could get a way with 12 gauge. Although everyone uses 10 gauge and so does Aero recomendations.
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Old 03-16-2015, 09:44 AM
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Default Re: Fuel Pump Wiring Double Checking having issue

Correct, the relay trigger wires require very little current to trip.

The amperage of the pump gets higher as the fuel pressure rises. At 80psi, I believe it gets close to 15amps. That's still far below a 12g wires 20amp rating, but I can see how Aeromotive would recommend a heavier gauge in case of crimping, heat, oxidation, etc.
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