Spyder 4G64 Spyder GS Fuel Pump Relay Module Bypass

Disclaimer: This documents mods made by me. I make no claims about any mods you make on your car that follows my process.

Hours were spent trying to trace the cause of our performance problems on our 1999 4G64 Spyder GS. The car would run great, switching from open loop to closed loop, until it warmed up. Then it would stumble and die. Since the problem was happening starting at different temperatures, it was not easy to pinpoint. Once, when I went to unplug the OBDII logging cable, I about burned my hand on the Fuel Pump Relay Module, which has a metal case. I knew something was wrong.

In 1999 (and 1993-97 for Galant), Mitsu added a Module to control the Fuel Pump Relay. We have been unable to determine the need for it, but some quick research indicates it was an attempt to vary the voltage to the Fuel Pump Relay in order to throttle the speed of the Fuel Pump.

Here is what the Fuel Pump Relay Module looks like, with the cover removed

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Here is how the fuel circuit is wired in the 1999 4G64

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Complicated. By unplugging the Fuel Pump Relay Module, and making three connections, you can eliminate the need for the Module, and just use the Fuel Pump Relay, like all other DSMs.

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Your Fuel Pump Check Connector will still work. Keep in mind that the Fuel Pump will now run with the key in the "ON" position.

If you are going to upgrade to a GST or GSX ECU, keep in mind that Pin #8 on those ECU's is a switched ground, so you could make your new grounding connection (#4) on Pin #8, and the Fuel Pump would only run when the engine is cranking.

Hopefully this helps save hours of time for someone who is having mystery rough-running, or no-start issues on their 4G64 GS.

 

[Justneedthisfixed]

Where exactly is this module located?

 

[DogWhistle]

Where exactly is this module located?

Under the driver's side console cover. Next to your right knee as you sit in the driver's seat.

 

[steve]

If you are going to upgrade to a GST or GSX ECU, keep in mind that Pin #8 on those ECU's is a switched ground, so you could make your new grounding connection (#4) on Pin #8, and the Fuel Pump would only run when the engine is cranking.

Interesting, this is a variable speed controller for the fuel pump. Did you have a stock fuel pump or something aftermarket?

With the GST/GSX ECU's pin 8 is pulled to ground whenever the ECU thinks the fuel pump should be running so you should connect pin 2 on the Fuel Pump relay to pin 8 on the those ECUs.

Do you know what the voltages are on pin 8 with the 4G64 ECU? Is the ECU or the control module sourcing the control voltage and is it a pulse train switching on and off or a varying voltage?

 

[DogWhistle]

Yes, Mitsu did a ‘pulsed’ approach with this relay. I had a stock fuel pump with factory wiring. Since the circuitry in my module was fried, I couldn’t determine if it was the module or ecu that pulsed the voltage. I didn’t measure voltage on Pin 8 on the 4G64 ecu since I wasn’t planning on keeping it installed.

Eliminating this relay gives you a choice to either ground on Pin 8 on a GST or GSX ecu, or to run a wire to ground to the body with the 4G64 ecu. As mentioned, if grounding to the body, the fuel pump will run when the key is in the Run position, even if the engine is not rotating.

 

[NVdsm]

Sorry to bring this back from the dead. Do you have a picture of how this is bypassed? I need to bypass this on my sons car but don’t know how to read the wiring diagram

 

[DogWhistle]

A picture was almost impossible to get to show this accurately because the two black wires you need to work with both have color stripes that aren’t visible from all angles.

For specific help, please DM us and we’ll go from there.