Fuel Pump Relay

** Update - I wouldn't do this modification again **

** This has pictures from the 165 and so wire colours may vary between other GT4 models **

What is this modification for?

The voltage applied to the fuel pump is reduced by a resistor, (click for picture), so the pump supplies less fuel. At some point the ECU determines that the fuel delivery is not adequate and flicks over a relay which then supplies battery voltage to the pump, so more fuel can be delivered. If modifications are made then fuelling becomes more and more important.

The voltage supplied to the pump through the dropping resistor is ~9V, and this then rises once the relay clicks over to ~14V.

Supplying little or reduced fuel may not be adequate for your modified engine and the time that the relay takes in flicking over and then starting to speed up the fuel pump may be too long. Modifying the relay so that the pump runs constantly at the battery voltage helps the fuelling.

Any downsides?

As you will be modifying the relay to supply the pump with constant battery voltage the fuel pump will be running at top speed constantly, thus shortening its life. Is this a problem? No. 18 months/20,000 miles and the pump is still running fine on the car. I have yet to hear of anyone having a problem with their fuel pump after completing this mod.

Another downside is probable over fuelling, particularly in the mid rpm range...

How do I sort it?

The fuel pump relay is behind the intake manifold mounted on the firewall - it's labelled clearly on the front of the unit.

Relay location. Relay and connector indicated Relay removed The underneath of the relay
Remove the cover by carefully folding back the metal tabs keeping the plastic cover in place Under the cover is a rubber seal which makes the plastic housing difficult to remove Connect the black/yellow wire to the red wire as shown

Undo the relay mounting bolt and remove the relay from the wiring loom. Turn the relay upside down and prise the metal clasps away from the side of the relay. Pull off the plastic cover, this seems like it won't budge, but that's only because it is stuck to the rubber gasket - give it a firm tug! Now you can see the wires coming from the bottom of the relay. Connect the two wires together - black/yellow to the red wire.

Note - use a thick piece of wire and solder this securely in place. Look at the existing wiring and size it appropriately. If in doubt about the size of the wire, go big!

Take the car for a test drive, making sure to get the turbo up to pressure at least once.

Job done.

Anything else?

The dropping resistor for the fuel pump can now be removed to free up a little room in the engine bay. This is also a handy place to mount the Water Injection relay! The resistor is located on the right hand side of the engine bay next to the diagnostic connector.

Fuel pump dropping resistor

The wire colours that connect the Fuel Pump Relay to the loom are:

Relay Loom
Black/Yellow Blue/Orange
Blue Blue/White
Red Blue/Black
White/Black Blue/Red