2nd Generation Specific (1986-1992) 1986-1992 Discussion including performance modifications and technical support sections.

another approach to fuel pump rewire

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Old Dec 23, 2007 | 10:40 AM
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another approach to fuel pump rewire

Just trying to find a less tedious way to rewire the fuel pump to have full voltage. This has probably been suggested before but usually appears in text and is hard to make sense of.

Been looking at this a while and trying to find a configuration that allows leaving everything where it is and just adding in the extra larger gauge wires.

Would the setup shown work?

Everything would have the same common ground reference.

Attaching the 12V from the battery when the relay is triggered by the stock 12V supply signal and tying into the same common +Voltage supply coming through from the stock resistor.
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Old Dec 23, 2007 | 10:41 AM
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where are the pics?
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Old Dec 23, 2007 | 11:08 AM
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D'oh

Pic Attached
Attached Thumbnails another approach to fuel pump rewire-fuel-pump-diagram.jpg  
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Old Dec 23, 2007 | 03:03 PM
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EDITED......mistake corrected.

EDIT: Seems it should work. But I always find it interesting that theres always a large gauge wire involved in doing this type thing,............but the power still passes thru the contacts inside a little relay then on to the pump.

It's occured to me that just buying a new circuit opening relay and resistor/relay would be just as good an idea as the moving the whole outfit to the rear of the car etc. I'm talking new contacts in new relays vs ten/fifteen year old contacts in old relays.

I say "press on and see how it works out for you".

Last edited by HAILERS; Dec 23, 2007 at 03:12 PM.
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Old Dec 23, 2007 | 05:03 PM
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Yeah I guess the wire doesn't have to be that large of gauge, probably could get away with 14 even, and I agree it is pointless if it is going through a relay that is equivalently smaller gauge wire, they should be matched in current rating.

Part of it though is having a direct ground lead to the battery, this just allows the current to flow through the pump without additional resistance that might occur by going through the frame to ground and then to the battery and takes care of the problem of possibly having a poor ground for the pump, and would help
response time as well for when the 12V bat source is made, though probably not noticeable.. I guess if just going with a new resistor/relay wouldn't hurt to run the ground back to the battery for the fuel pump anyway.

I'll post up my results after I get a chance to do this.
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Old Dec 23, 2007 | 05:40 PM
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I'm sure you'll get other views other than mine on this. Just wait and see. It never hurt to have other opinions.
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Old Dec 23, 2007 | 05:55 PM
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Originally Posted by kleetuz
...I agree it is pointless if it is going through a relay that is equivalently smaller gauge wire, they should be matched in current rating.
You're assuming the stock relay is insufficient. Given its physical dimensions, and having seen inside one, I'd say it's more than sufficient. The stock pump's only drawing ~8A.

Part of it though is having a direct ground lead to the battery, this just allows the current to flow through the pump without additional resistance that might occur by going through the frame to ground and then to the battery...
You think the entire body has more resistance than a single wire? Not a chance... Running a whole new ground wire is just a waste of time.

...and takes care of the problem of possibly having a poor ground for the pump...
You can take care of that by simply doing a good job on the ground point.

Personally I think relocating the resistor and relay is a minor thing, and it gave me needed room for my intake. It also eliminates the voltage drop on both low and high speed settings, unlike this method which only treats the high speed. No biggie though.
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Old Dec 23, 2007 | 07:47 PM
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You think the entire body has more resistance than a single wire? Not a chance... Running a whole new ground wire is just a waste of time.
************************************************** ***************
There's a lot of truth in the above. I can take a Fluke with two twelve foot meter leads and touch a F-16 airframe, say near the right fwd hardpoint and the other lead aft of the wheel well, and the meter will read less than 0.3 ohms. I've had to do this in the past to convince certain people they were tracking down a non existing problem.

Then again I've seen ground points with paint under the wires lug cause *THE* problem. Rare, but it happens.
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