okay I have a 92 SC400 that won't start so after doing some research I thought I would troubleshoot the fuel system. When I turn the key on I can't hear the fuel pump running so I decided to try the FP ECU bypass to see if it's the pump or the ecu that is causing the problems. Now when I turn the key on I hear the fuel pump running, but when I turn it off the pump will continue to run until I either disconnect the battery or remove the EFI relay. I'm pretty sure the system isn't suppose to work like this. Does anyone have any idea what could be causing this?

 

would this likely be a fuel pressure problem or an electrical problem?

if electrical is the likely culprit a grounded wire, bad sensor or a bad engine ecu

if it's the ecu is there a diy test for the ecu or do I just need to replace it and see what happens?

 

I'm having a similar problem.

My Fuel Pump ECU shat out on me a while back and i ran a jumper wire to the fuel pump in the fusebox to bypass the ECU.

the car ran fine for a little while, but it seems like once it warmed up, and even while driving sometimes, the car would shut itself off and I was not able to restart until some time later or even the next day. The fuel pump relay was excessively hot as well. (possibly a faulty relay?)

I then noticed that with the car off, I could hear my walbro fuel pump continuing to run, making me think that the jumper wire was directly draining the battery, with the key on, engine off. So i'm kind of in the same boat as you.

Before I do the 12v mod to the ECU i'd like to know if it causes the same problem that we are experiencing - I currently have a parasitic drain on my battery and would like to fix it, so if the 12v mod is the answer, someone please let me know