Hello,

I have searched long and hard for an answer to this, but I am officially stumped.

A while back I did the 12v mod on my fuel pump. This created no problems for me. Since then I have installed aftermarket headlights, and that is it.

Yesterday, I turned off my SC and noticed the fuel pump was still running. It didn't shut off until I pulled off the round, gray cylinder in the farthest to the right slot in the engine fuse box.

Every time I get out of my car I have been doing this, since I don't want to kill my fuel pump or my battery.

Thoughts?

Thanks,
Tim

 

When you say you did the 12v mod, how did you do it? Maybe some details around this would help answer the question.

 

^^ Seconding RXRodger. The right way to do the +12V Fuel Mod is to wire it up so as to use your stock SC fuel ECU bypassed but retained as a safety and control trigger for a 30/40A automotive relay which will carry the main current to your fuel pump.

 

I disconnected the ECU from the harness and jumped two of the connections on the harness together.

 

My current fuel ECU is fried, am I still able to do it like this?

 

It depends on whether or not it was burned due to too much current or blown capacitors and if you can repair it. I'm not sure if the main ECU will still be able to control it correctly if it has a malfunction. The capacitors should be replaced inside it if they hail failed and are leaking.

There is a procedure for repairing the SC300/400 Fuel ECU here:

https://www.clublexus.com/forums/sc-...rt-itself.html

Barring that you can always get a used working one off ebay.

Technically using the +12V Bypass Mod with a relay will take the current load off the factory fuel ECU and should allow it to last longer as just a safety control device.

The reason it's better to retain the safety control function of the fuel ECU is because it in stock form or it when combined with a 12V Mod w/Relay disallow the pump from staying running if the engine shuts off. This is especially important if the car is ever in an accident. Something none of us ever want to think about but with a fuel pump it is better to be safe about things like this.

 

For the time being I have wired in a switch that I toggle every time I get in the car. I'll just do this until I get a new fuel ECU.

If I get in a crash before then, hopefully I'll have the presence of mind to turn off that switch.

 

You could use a weldon or aeromotive fuel pump ecu instead. Both use a RPM input, so if the engine stalls or turns off it kills the fuel pump. It's a more expensive option, but probably more reliable.