Well I had my car running great yesterday and today I went to start her up and the fuel pump came on like normal but the starter wouldn't engage (problem with my starter usually means wiggling the high current connections as I need a new one) but anyways when I turned off the ignition and took out the key the fuel pump continued to run. I unplugged the battery and when I replugged everything the fuel pump would not run regardless of the keys position. The only change from stock I have in the fuel pump relay wiring is that I ran a hot wire (when ignition on) to the white/green wire on the relay to allow the pump to run at all times through my fuel pressure regulator but this setup has been working for about a week. Any ideas?

Thanks in advance!

 

Try the Oil Pressure Sending Unit (OPSU). The OPSU is located either on the china wall atop the intake or above the oil filter. There is a direct connection from the battery to the fuel pump through the OPSU. The fuel pump can run regardless of the relay, and even regardless of the key, as this circuit is connected directly to the battery and not in the ignition circuits. Thus, a bad OPSU can keep the pump from running - AND a bad OPSU can also make the pump run continuously regardless of the relay or even the key.

My 1992 - when I first got it the battery would drain every 3 days - took me a few weeks but I finally figured out this OPSU circuit - the OPSU was bad, and "thinking" there was oil pressure it made the fuel pump run 24/7 until the battery drained dead.

New OPSU about $30.

FYI - to make my fuel pump run, and delete this OPSU circuit that could fail - I cut the fuel pump wires from my OPSU (the two larger wires), and ran them into a factory relay with a ground and a hot-in-run. Now, when I turn the key, the hot-in-run energizes the relay, and makes the OPSU fuel pump connection for me - that way a bad OPSU will never drain my battery, or ever leave me stranded with no fuel.

Make sense?

 

Gotcha I am going to take a look in the morning. I have a feeling I may have fried an in line fuse today though. The car was starting up perfectly normal yesterday, but I realized what may have happened today. I spent some time tucking in some wires temporarily and forgot to tape them up before I tried starting the car. There were some random fast ons that may have been shorting against the body. It was right after this attempted start that the starter did nothing and when I pulled the key out, all the dash lights (Service engine soon, Brake, and seat belt lights) remained on and the fuel pump as well. I unplugged the battery and moved the connections out of where I thought they were shorting and when I reconnected the battery everything was normal except the fuel pump would not turn on and the starter would not do anything at all.

 

I sanded my ground points and bypassed the OPSU and the Relay and ran a hot in run to the fuel pump. Works great now! Thanks for the help.

 

camaro newbie has a good point and good info there to help with a bad OPSU if it ever happens to you.

this will work great.


the OPSU allows the pump to run after crankin and starting time.

it is supposed to cut power off to the pump when the rpm is next to nothing or is zero

by rpm i mean oil pressure