How to properly rewire your aftermarket fuel pump

[lagos]

Aftermarket fuel pumps such as the Walbro or the Denso OEM Supra pump flow a lot more fuel then the factory fuel pump our cars came with. This also means that they draw more current then the factory 16 gauge wiring can support. I ran a few voltage drop tests between the battery and the fuel pump wiring and noticed that, just at idle, I was loosing around 1v to 1.5v of power between the battery and the fuel pump, because the factory wiring was not sufficient enough for the extra load created by installing a high flow fuel pump.

I decided to rewire the fuel pump to have its own dedicated power source directly from the battery using 12 gauge wire, a 20 amp fuse, and a 30amp relay.

First I started out by connecting 12 gauge ring connectors to my 12 gauge wire. I crimped the connection making sure there was some wire still sticking out, and then I soldered the remainder of the wire for a secure connection. This is one of those things that you really have to do the right way. Crimping alone could come loose from all of the vibrations of the car.
You will need two ring connectors. One for the relay ground, and one for the main power wire connected to the battery.





I ran brand new 12 gauge wire from the battery, through the firewall, along the door still, and to the back seat area of the car with a 12 gauge fuse holder and a 20amp fuse that I bought at Walmart. Just be sure to wait until you are finished wiring, to connect this to the battery.



Then I wired up my relay. The idea here is to connect the wire from the battery and the wire that goes directly to your fuel pump to the "switch" part of the relay, then connect your factory fuel pump wire and use that to trigger the relays magnetic coil as power, with a new ground wire from the relays coil to any ground point on the car.



I found a bolt under the rear seats that would work perfectly for a ground and bolted my ring terminal to it, with the wire running to the relays magnetic coil ground wire.



Then I cut the factory power wire that goes to the fuel pump and connected the end that goes to the pump to my relays switch normally open wire, and used the end that would normally power the fuel pump to trigger the relays magnetic coil. This way, when your cars factory wiring starts sending power to the pump, it will flip the switch, and supply power to the fuel pump from its own dedicated power source releaving the strain on the rest of the cars EFI wiring.



Then I ran the wire along the factory wiring route and hid my relay behind the interior plastics under the rear speaker.



... and wrapped up the wiring at the pump for a clean install.



Then I connected the main power to the battery and tucked the wiring off to the side.



I fired up the car and immediately noticed a difference. Prior to this, my safc would show a high of 13.5v on a cold start, and the voltage would drop down to as low as 11.5v once the car was warmed up with all the accessories on. This is the same efi wiring that also supplies voltage to the fuel pump. After rewiring the pump and offloading that power draw to its own circuit, I now get 14.5v at cold idle. Exactly 1v more then I had before!

[russiankid]

I like to put heat shrink tubing on the connector as well. The plastic part of the crimp isn't exactly weather proof.

[TalonTsi97]

Nice writeup, I was already planning on doing this at least once in the next few months.

[lagos]

Originally Posted by russiankid

I like to put heat shrink tubing on the connector as well. The plastic part of the crimp isn't exactly weather proof.

I did on the ring connector that goes to the battery, but there was no need to do it on the one that supplies a ground to the relay.

[russiankid]

Originally Posted by lagos

I did on the ring connector that goes to the battery, but there was no need to do it on the one that supplies a ground to the relay.

Oh ok good. I am anal about stuff so I would have put it on ground too, and probably some di-electrical grease to prevent corrosion.

This is a good thread for people to see how electrical connections should be made. Electrical tape sucks over time so I wouldn't recommend using it. When soldering you're looking for a clean connection. Here is a pic I snapped when I did my HID harness:


It should look clean when done:


/thread jacking.

[lagos]

No problem with the thread jacking. I love wiring porn.
I should take a few picks of the harness im doing right now. Totally rewiring a 1990 3sgte wiring harness to mate up to a 1994 celica car. Its a big project. Takes a long time to figure out how each car works and convert everything over.

[Got Insulin?]

Good write-up, man. They ought to make this a sticky.

[russiankid]

Originally Posted by lagos

No problem with the thread jacking. I love wiring porn.
I should take a few picks of the harness im doing right now. Totally rewiring a 1990 3sgte wiring harness to mate up to a 1994 celica car. Its a big project. Takes a long time to figure out how each car works and convert everything over.

I am no where that level yet.

The harness I made was to illuminate the computer from telling me my low beams our out when HID's are installed. Many people spliced in bulbs and such to trick the computer since it reads resistance. Instead, I made a harness that can be removed and doesn't hack the stock wiring.

[TROLL]

Nice informative post, thanks for contributing. Moved it to the electrical section of the forum as I feel this tech info fits better there.

[lagos]

Ah, you killed it! No one ever checks the electrical forum! haha

Anyway, the really cool thing about wiring it up this way is that you fully retain all the benefits of your factory setup. Things like fuel cut, or fuel pump dignostic boxes will still work like stock.
This is also the same way that toyota wired up its denso pump in the Supra by placing it on its own EFI2 relay with its own fuse. So clearly there is a need to do this with an upgraded pump.

[frosti108]

nice writeup. ive been running a walbro 255 in my s13 with stock harness. so if I ever get it running again, i'll definatly be doing this. best part is, my battery is right in the hatch less than a foot from the pump

one random question, in the 7th picture, what is that little spool of wire? i found a couple of those that i thought were solder at 1st, but I think they are something for a speaker...?

[lagos]

Its solder.
Radio shack also sells spools of speaker wire, electrical wire, etc... So you just have to read what it says on the package.

[lagos]

Btw, I HIGHLY recommend getting one of these butane soldering pens. Radio shack sells them for 20bucks. Its one of the best things you an own. Not only is it super portable, but will solder through almost any gauge wire without a problem.


Now I just need to get myself one of those mini torches for heatshrink tubing, because using a lighter takes longer and leaves burn marks.

[DC2.2GSR]

nice writeup! i just did this to my own car and my buddy's RB S13. it's a huge help to get that draw off of the system onto its own circuit, it's great that you posted the SAFC pic as proof.

good call on the butane solder pen too. i've used some of the best soldering irons ever made, weller, snap-on, etc... none compare to the speed and control of a good butane pen. i've used a few different kinds in the past, but i've been stuck with a crappy $8 harbor freight one temporarily since i accidentally ran over my good one. i'm an idiot. lol.

[lagos]

Yeah they effing rock. Best thing for soldering, and it fits in your pocket. The only thing that its really not great for is for circuit board soldering. It puts out a little bit too much heat for such detailed work, but for anything car related, you cant beat it.

[frosti108]

Seems to me that as long as I use flux, any soldering gun works awesome.