How to rewire your fuel pump for max efficiency!

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shift_down
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How to rewire your fuel pump for max efficiency!

Post by shift_down »

Most of our 240s are decades old, and it is no surprise that the wiring in our cars are worn down and deteriorating.
The fuel pump is essential to delivering the correct amount of fuel to your motor, ESPECIALLY during boost. To make sure your car is not running lean do to not enough fuel being pumped out by your pump, I highly suggest re-wiring your pump.

Step by Step instructions:

FIRST you will need to gather all your supplies. This includes:
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Bosch 40 amp relay with 4 prongs
Heat shrink or butt connectors (I HIGHLY recommend heat shrinkers)
12 gauge wire, yes I said 12 gauge
Soldering iron
Electrical solder material
Butt connectors
20 AMP inline fuse

Remove negative terminal from battery before you begin!

Step One:
Empty your trunk and pull the carpet and board out to expose your fuel pump cover. There is no need to pull the fuel pump out.
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Step two:
Unscrew the cover to the fuel pump wire harness. There are two covers, unscrew the one on the right next to the strut.

Step three:
Unclip the blue plug

Step four:
Locate the power wire. It is the white/purple wire.
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Cut that wire in half. Now you have one portion of that wire going towards the fuel pump, and the other portion going towards the blue clip.
Solder the 12 gauge wire to the positive wire that is connected to the fuel pump and then connect the other side of that 12 gauge wire to pin 87 on your relay. Solder the other portion of the positive wire that connects to the blue clip to a 12 gauge wire, and then connect the other side to pin 86.

Step five:
Connect a 12 gauge wire to your battery and run a 20 amp in-line fuse on that wire, then run the other side of that to pin 30 on your relay.
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Step six:
Connect a 12 gauge wire from your negative battery cable and connect the other side of that 12 gauge wire to pin 85.

DONE!
This is what it looked like when finished. I screwed my relay into the fuel pump cover to hold it tightly in place.
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Notes:
I made my own in line fuse by getting two butt connectors and connecting them to a 20AMP fuse. This is ghetto, but its what I had and works:
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I connected butt connectors on my relay prongs to make it easy to connect the wires:
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Here is a diagram so you can visualize it better:
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MAKE SURE TO PLUG THE BLUE CONNECTOR BACK IN WHEN YOU FINISH

I recommend you test voltage at the fuel pump before and after this mod if you want to see the difference.
Last edited by shift_down on Thu Jul 04, 2013 9:01 pm, edited 2 times in total.
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Re: How to rewire your fuel pump for max efficiency!

Post by Rick »

Sticky! Good write up!
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Re: How to rewire your fuel pump for max efficiency!

Post by Marcus »

I'd be timid with the spade terminals unprotected so close together. To help I will bring my electrical pigtail book back with me tomorrow so we can have a part number to use or x-reference to make this even better. Great write up!
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Re: How to rewire your fuel pump for max efficiency!

Post by airman »

Nice write up shift.
Marcus wrote:I'd be timid with the spade terminals unprotected so close together. To help I will bring my electrical pigtail book back with me tomorrow so we can have a part number to use or x-reference to make this even better. Great write up!
When I did mine, I soldered the wires to the relay and ran heat shrink over them. You could also get the plastic insulated ones, or a relay socket 'pigtail' if you will that has the bare wires coming off of it.
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Re: How to rewire your fuel pump for max efficiency!

Post by shift_down »

I heat shrunk them after putting the butt connectors on, I didn't trust them just hanging out like that either.
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Re: How to rewire your fuel pump for max efficiency!

Post by Marcus »

Ahh I see. Well carquest has a 4 wire pigtail number S-706 and a 5 wire pigtail number S-654. I assume the 4 wire excludes the center terminal. Edit: I hope other stores can cross reference the numbers...however this might help.

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Also if someone would want to get perfectionist style on the fuse as well....I have this information to offer.

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Last edited by Marcus on Wed Jul 10, 2013 4:36 pm, edited 2 times in total.
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Re: How to rewire your fuel pump for max efficiency!

Post by shift_down »

I've never heard of those before, I'm going to check them out.
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Re: How to rewire your fuel pump for max efficiency!

Post by airman »

You can probably find them at a local auto parts store. But I'm sure they're $10+
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Re: How to rewire your fuel pump for max efficiency!

Post by toky042 »

nice write up :)
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Re: How to rewire your fuel pump for max efficiency!

Post by chillmieste »

sweet write up may have to do this to mine. i go through walbros like every 8 months
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Re: How to rewire your fuel pump for max efficiency!

Post by Niys »

I this for just the stock pump or is this something to do for you aftermarket ones as well.
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Re: How to rewire your fuel pump for max efficiency!

Post by shift_down »

It affects the wiring, so anything at the end of the positive wire gets affected.
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Re: How to rewire your fuel pump for max efficiency!

Post by airman »

Niys wrote:I this for just the stock pump or is this something to do for you aftermarket ones as well.
You definitely want to do this with aftermarket fuel pumps, but it couldn't hurt for stock ones. If you're running boost, you should at least have a Walbro 255 or something.
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Re: How to rewire your fuel pump for max efficiency!

Post by BrokeKAT561 »

Damn I did that and it worked out so much haah, before I was putting straight power from the battery, and have a switch so if I forgot to turn it off my battery would die haha!
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Re: How to rewire your fuel pump for max efficiency!

Post by slo240 »

Right now my car is leaning out at wot, would this rewire fix that?
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Re: How to rewire your fuel pump for max efficiency!

Post by jmac636 »

If your leaning out going WOT then its either the wiring to the fuel pump or the fuel pump itself going bad. Its common for the wiring to have a bad connection and dropping voltage. I like to redo the ground wire also. Great write-up btw.
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Re: How to rewire your fuel pump for max efficiency!

Post by mig_100 »

Great write up. You can also wire in a kill switch in this location
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Re: How to rewire your fuel pump for max efficiency!

Post by street_240sx »

So what's the point of this? Is it just to have new wires for you fuel pump?
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Re: How to rewire your fuel pump for max efficiency!

Post by shftqikr »

Jut noticed this write up. Great way to avoid voltage drop on the fuel pump. This is a classic DSM move on 1g's. How much of a voltage drop was recorded before and after this mod?
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