Thread: inline fuel pump relay issues

this is for an s13.

its an sr, of course, but i dont think that matters with this problem.
i was having problems with low voltage at the fuel pump under high load after 5k rpms. so i jumped it from the battery and it ran like a champ. since it was a voltage problem, i installed an inline relay from the battery to the fuel pump and voila! problem solved. now heres the issue - when i turn off engine with the key, the relay continues to provide voltage to the pump and the car continues to run. if i put it in gear and kill it that way, the voltage goes away - like its supposed to. i checked and double checked the relay and its wired correctly. even tried a spdt relay and a spst relay and the problem persisted. i really dont want to install an inline switch, but its looking like i may have to.
anyone else have an issue like that?

Havent had an issue like that. You said you wired straight from the battery?

Make up a wiring diagram with relay part number. So we can trace it out.

A relay is a switch... So either you keep grabbing bad relays that stick and/or there is a mis-wire.

you need to wire up the relay so it steps up the voltage. I have mine wired this way with the stock fuel pump relay in place. you take the power going to the pump and run it through the relay which get direct battery voltage. So the stock relay turns on the the inline relay and when the stock relay turns off so does the in line relay.

here is how the inline relay should be wired. iirc the red/black wire is the power for the fuel pump. I usually grab the pump wire from under the back seat.



Relay Diagrams - Weak Positive Output to High Current Positive Output

cotrim had it right on the nose. Use the stock wiring to and at the fuel pump to turn the relay on and off. Supply the relay for the pump directly from the battery with a thicker gauge wiring. Use a heavy duty relay. If your ecu is commanding things correctly such as turning on and off the fuel pump then there is no reason this setup wont work. I have my inline pump wired this way and it works absolutely flawlessly with zero issues.

sorry, i never came back here and responded after i got it resolved...
it was actually very easy to do. i took a relay - spdt i think and then wired it in the trunk next to my battery. all i had to do was interrupt the 12vdc supply wire for the fuel pump and voila! done. full 12 volts to the pump and it runs like a raped ape.

to clarify - i was using the 12+ ignition as the trigger and that wasnt correct. instead of using 2 different wires, all i needed to use was the supply wire as the trigger and interrupted wire... make sense? lol

Glad you got it figured out.

thanks! me too. ever since i installed the lsx coils and fixed my fuel pump - i havent wrenched on the car at all and the evo has been sitting in the driveway. lol its WAY more fun to drive than the evo is, thats for sure.