The fuel pump is the most vital part of your EFI system, because if you don’t have the pump and fuel pressure your ECU is expecting you will have problems. By popular demand, we’ve brought back and revised one of most popular How To and DIY articles, How To Rewire a Fuel pump. The process of completing this task is very easy and straightforward once you understand what you are trying to do.
What Does Rewiring your Fuel pump do?
The act of rewiring a fuel pump is simply replacing the power or feed wire to a larger gauge wire. Because your stock wire is thin and can struggle to carry the much needed voltage to your fuel pump under high boost, your fuel pump performance can suffer under load. We’ve tested stock fuel pump setups on our Dynojet 448X dynamometer, and found voltage can dip to as low as 9 volts during a dyno pull.
What will you need? Larger gauge wire, and inline fuse and a relay is about all the parts you truly need to complete this job. Many people replace their stock fuel pump wire with a larger gauge wire ( 10 gauge is recommended ) and run it to the fuel pump and think they are done. The problem is when you run just a wire or even a wire with an inline fuse to your fuel pump, you can cause other electrical problems elsewhere in the car.
These problems can range from annoying issues, like your electrical devices not working properly or intermittently, to dangerous as in fire. Always rewire your fuel pump using an automotive grade relay to prevent these kinds of problems.
To begin our how to rewire a fuel pump guide, take a look at your automotive grade relay. Most of these kinds of relays are known as single pole double throw, meaning that there’s a single feed and a dual output. These relays can be found at any automotive store and even your local hardware stores as well. Sometimes the identification on the terminals and poles may be switched or numbered differently, but the relay acts in the same manner.
There should be 5 terminals in total on your relay, and we’ll be explaining what the relay does and what each relay terminal does.
Terminal 30 or the feed pole on your fuel pump relay is what we’ll start with first, and this terminal should be the one supplying the power from the battery or switched power source. Because this wire is constant and high voltage, use a 10 gauge wire and solder in an inline fuse to your 30 relay terminal.
The next terminal we will be wiring on your relay is the 85 pole, which should be wired to your vehicle chassis for the low reference or ground signal. When you have this wired, you are ready to start digging into your stock wiring harness for the final part of our how to rewire a fuel pump article.
The last part of our guide requires you to find your stock fuel pump harness and then locate the power wire for your fuel pump itself. If you need a guide on how to install an aftermarket fuel pump, check our How To Articles to check out the vehicle you own.
We’ll be briefly showing you how to access the fuel pump in a 1997 Nissan 240SX, equipped with a SR20DET JDM engine swap. To reach the fuel pump and fuel pump harness, open your 240SX door and slide the driver seat forward as far as it will go.
Now reach under your back seats and undo the clips and 12mm bolts that hold the back seat in place. Remove the back seat to access the fuel pump cover.
Undo the 10mm hex screws here ( there’s 4 total ) and remove the fuel pump access plate to expose the fuel pump and the wiring harness.
The harness you pull off must be tested with a ohmmeter or a voltmeter to determine the power wire in the harness. This particular application is using a black wire with yellow stripe as the power wire from the ECU, this wire must be run to the 86 terminal of your fuel pump relay. This acts as the trigger because it’s a switched power source, and the relay will kick over to use the 30 position power wire when this trigger is activated.
Now run the 87 pin to the other side of that fuel pump harness, which leads to the fuel pump itself. Try to limit the distance between the 87 terminal and your fuel pump wiring, because the longer the stock wiring is the more of a potential voltage bottleneck remains.
The single pole double throw automotive relay has many uses, and can be used in a variety of different ways so if you see instructions on how to wire a relay and they differ from this one, don’t worry. Here’s the complete fuel pump relay wiring schematic and wiring diagram in case you want to figure out your own use.
Rewire Fuel Pump with SPDT Relay
- 30 – feed wire
- 87A – Normally Closed (NC) terminal
- 87 – Normally Open (NO) terminal – the wire that the relay switches to when the relay coil is energized
- 86 – relay coil
- 85 – relay coil
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