Wiring fuel pump seperate

[Murse]

How it work if I wanted to run my fuel pump on a seperate circuit to a switch. So I would turn on the switch and power the fuel pump, how could I do that without the computer getting mad?

 

[jirwin]

I used the existing fuel pump relay pins to trigger another external relay that gives the big boy fuel pump power. That way I could retain all normal triggers and safeties. The ECU will turn off the fuel pump without a crank signal after a few seconds. Thats why turning the key it "primes" and shuts off. Its a safety feature so if you wreck it doesn't keep pissing fuel everywhere quite literally adding fuel to the fire.

 

[Gtstorey]

What's the purpose of the added switch and which fuel pump are you talking about. LNF has a two, the intake pump and the high-pressure pump.

 

[Murse]

The original builder messed up the wiring so my intercooler pump and fans turn off with the dash lights. So to make things easier im going to add a panel and control that system on its own, figured I could do the fuel pump on that system also. Kinda for cool factor also

 

[Gtstorey]

Cool until what jirwin pointed out happens. I would have to check the wiring diagrams to see how the circuit works to see if it looks like the ECM even knows whether it is being triggered. There often isn't any check to see if the fuel pump is being powered if you don't have a fuel pump control module.

Depending on what you exactly mean by shutting off with the dash lights, it sounds like the intercooler pump and fans may have been powered off the fog light circuit.

 

[Murse]

So when you turn the automatic headlights off, or if the sun is out and the dash lights turn off. The intercooler pump turns off and the heat exchanger fan turns off. I am adding another 2 heat exchangers on the sides of the engine bay and for the life of me cannot figure out where he wired things wrong. I have also dealt with some other wiring problems, had to rewire the pedal>throttle body curcuit. I'm almost certain that he shorted something out (probably to ground) but cannot figure out where. I will rewire the car this winter but I like keeping things simple, and its kinda cool to have to flip some switches to turn the car on hah.

I installed a new blinker handle/switch to see if that did anything but it didn't. Problem I am having is that it feels like there are too many systems involved that it could be and I don't want to unwrap the entire harness and start over. Any ideas that might be worth looking into would be great. Thanks everyone, this honestly feels like one of the best communities/message boards I have ever been a part of!

 

[Gtstorey]

If the fuel pump is working, leave it alone. What happens when you or someone else forgets to turn it off.

For the intercooler, find an ignition hot wire and use that to turn on a relay to power the fan and IC pump. With the appropriate fusing.

 

[Gtstorey]

But if you are dead set on a switch on the fuel pump, use a switch to interrupt the fuel pump relay signal. Takes away the negatives of a switched fuel pump, but still "racecar".

 

[Murse]

Every ignition wire I can find turns off when I turn off the auto headlights. Makes me wonder if he has that curcuit wired wrong

 

[Gtstorey]

If the car is still running when there are a lot of ignition hot wires left. I think the factory amp circuit may been what I am using. Have you looked a factory wiring diagram for your donor?

 

[Murse]

I have but just to see i used one of those fuse jumper wires and on any ignition fuse I can find power turns off when I turn off auto lights. Maybe I should just not mess with the fuel pump. The intercooler fans and pump I could just put on a switch. But you are probably right I should see if i cant just find an ignition power that is actually working.

 

[Gtstorey]

You may be missing a ground that is using the headlight or dash lights to back feed as a ground. I would start by ensuring every black wire in the BCM and Fuse box are connected to a good clean ground. But without know what you have checked, the IC may just be fed by the headlights, although I hope it is signaling a relay and not a direct feed.

I'm not sure of you level of electrical experience, but you don't typically want to feed fans through a switch. Intercooler fan probably can be with a good switch, but much better off to use relays.

 

[Murse]

why a relay instead of a fan? Just curious why a relay is better. electrical exp. is moderate but when I bought the car the guy specifically said he REEEEAAAALLLY struggled with the electrical side...and it shows. Electrical gremlins popping up EVERYWHERE.

 

[Ross]

A relay allows a thick high amperage wire to go straight to the load (fan or fuel pump), and a small low amperage wire to go to a switch or a transistor controller like we have inside the ECM or BCM. Adding a relay is good practice, as it reduces the amount of copper wire resistance, allows the switches to last longer, makes the wiring harness lighter and cheaper.