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Fuel Pump wiring question


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05 OBXT Limited: For a modest stage 3 tune (VF-52) on an otherwise stock fuel system, I want to make sure the fuel pump is not going to be a weak point.

 

 

 

My plan was to swap the stock FP to an AEM 50-1215 (340 lph) because it is direct-fit and seems to have a good reputation, but I want to ensure the wiring situation is safe.

 

 

 

I am looking to bypass the stock wiring and have a relay wired directly from the battery to power it, but I am unsure whether that is the best way to do things.

 

 

 

From my understanding, in the stock configuration the controller will send power to the pump in 3 intervals: 33%, 66%, and 100% depending on load. If I wire in a relay to switch on via that signal, it will simply send 100% to the aftermarket pump at all times. Is there any potential problem with this setup?

 

 

 

I know there is an iwire kit that preserves the low/med/high function but it's quite costly ($250)

 

https://www.iwireservices.com/product-page/fuel-pump-controller-hardwire-kit

 

 

 

 

 

Any advantage to the more expensive route, or should I just go with a simple relay?

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So there are a couple of things you can do.

1. You can just grab power directly from the battery with a relay and have the SoB run 100% all the time, YOLO bichess!!!

2. You can grab an STI fuel pump controller, these are said to have a lower voltage drop and just swap it in directly.

3. (Which is what I did). I swapped the fuel pressure controller with an STI unit, I ran parallel wires from the FPC to the pump connector under the rear seat so there is no voltage drop. And this is the important part you can run a larger parallel 12v wire from the front of the car to a relay in the rear. You can use the original 12v signal from the car to activate the relay, and have the new larger wire provide power to the FPC.

Hope that makes sense.

 

In my car I am relocating the battery to the rear, so I did not have to run a wire all the way to the front. I have a remote fuse panel in the rear for "activities" should I need additional circuits.

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So there are a couple of things you can do.

you can run a larger parallel 12v wire from the front of the car to a relay in the rear. You can use the original 12v signal from the car to activate the relay, and have the new larger wire provide power to the FPC.

 

Won't any signal (even the low idle) from the FPC just activate that relay, resulting in it running 100% all the time regardless?

 

 

 

 

2. You can grab an STI fuel pump controller, these are said to have a lower voltage drop and just swap it in directly.

I'm not sure I understand the benefit of swapping out the FPC. Is it that much different from the OBXT/LGT unit? and would it be different from just running another parallel wire on the stock unit's 12v line to minimize voltage drop? Would it get along with the stock ECU?

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Won't any signal (even the low idle) from the FPC just activate that relay, resulting in it running 100% all the time regardless?

 

 

 

 

 

I'm not sure I understand the benefit of swapping out the FPC. Is it that much different from the OBXT/LGT unit? and would it be different from just running another parallel wire on the stock unit's 12v line to minimize voltage drop? Would it get along with the stock ECU?

 

No, there are still other wires running to the FPC that control the operation (this comes from the ECU), the only thing you would be providing is a new source of 12v.

Now if you remove it and bypass it then yes it is 100% all the time.

 

Now your question about the STI unit versus the legacy unit, there are a couple of threads pages and pages long search is your friend. But the short version is people tested it, there is a difference.

 

 

All of your questions are answered in those threads wiring schematics, the whole bit, you should just go read that at this point.

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I’ve had a typical stg3 setup (UP/DP/exh/intake/vf52/pump/injectors/bcs etc) running on stock wiring and FPC for years - as long as pump and injectors are upgraded and you’re not going to a larger turbo you shouldn’t be running out of fuel.
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