How to properly rewire your aftermarket fuel pump Options

[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. EDIT: Dont use this type of fuse holder. Mine ended up catching fire after about a year of use! I replaced it with a higher quality fuse holder from radio shack and have not had any problems since.



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!



This post has been edited by lagos: Mar 18, 2013 - 11:11 AM

[95st-celica]

very nice!

[presure2]

good stuff art, i am planning on doing this very same thing when i do my install.

[cax_11]

Awesome write up.. any improvements in performance??

Reason for edit: no need to quote all the photos