Ok guys, here we go...

1989 Firebird, 305 TBI VIN code E

I just finished (so I thought) fixing all of the convoluted wiring mess that came with my new Firebird project so imagine my surprise that now my newly installed fuel pump stays on all the time even after I take my keys out of the car!

I just replaced the fuel pump relay and repaired the wiring to it. I just replaced the oil pressure switch above the oil filter. I cleaned all the oil out of the connector that the old leaking switch was depositing there one drop at a time.

Now my oil pressure gauge works (it didn't before.)

This problem just reared its head after an extended, high spirited test drive. Before the test drive, everything was working as it should.

I keep thinking it must be the oil pressure switch keeping the circuit "latched" on by a malfunctioning switch. Unplugging the relay did not shut the fuel pump off. I finally shut it off by removing the fuse next to the battery in its little connector.

My new oil pressure switch isn't for the fuel pump circuit is it? Surely not, with such little wires going to the sender. I was thinking it should be back near the distributor but my manuals aren't showing me the picture and I just can't see it through the maze of wires and vacuum hoses.

Anybody got any experience with this one? I've been searching but no one has put a picture of it up and I can't tell if they are talking about the one above the filter that I just replaced or a different switch behind the manifold. Maybe the TBI engine uses a different one? I just am not seeing it...

Thanks for the help guys!

 

Ok, update...

I just went out now that the car is cooled down, plugged in the fuel pump fuse next to the battery, and... nothing. Which is exactly the way it should be.

So now the question has changed slightly. Why does the fuel pump stay on after the car is warmed up, but not when its cool? Oil pressure switch seems to be number one on my list and I'll check it next.

I just don't see how the switch next to the oil filter can be the one. The wires are small and doesn't a switch that runs the gauge AND an oil light need three wires? Not sure, but I guess I'll start ripping through the wiring and vacuum lines tomorrow morning.

Any help out there?

 

Drove it today, and nothing unusual.

I got to the back of the engine where the older chev engines used to have an oil pressure tap and there's just a pipe plug there. I guess my NEW oil switch on the side of the engine was the culprit, as I just don't see anything else in the schematic or on the car that could do it.

 

The Oil Pressure Sending Unit on your car is a 3-wire unit - one wire sends signal to the guage, the other two (which are slightly larger guage wires and red and orange I believe) control the fuel pump. This is a backup system so that you'll retain fuel pump if the ECM or fuel pump relay circuit goes bad. The OPSU senses oil pressure and will run the pump if it's not already being run by the ECM/relay circuit. This connection between fuel pump and OPSU has a direct uninterrupted path directly to the battery, as you have witnessed with the fuse there by the battery.

If the pump continues to run after the car is turned off, and you're not way overfilled on your oil, then you have a bad OPSU, even though it's new.

Also, if the pump will not run without that fuse by the battery in place, then there is something wrong with your ECM/relay fuel pump circuit. Remove the fuse by the battery, and see if the pump primes - if it does, then see if car starts and runs without it. If it does, great. Keep the fuse out, but don't lose it - I suspect there's an issue with your ECM/relay circuit as the OPSU circuit should not work if the ECM/relay circuit does.

You can replace the OPSU again (try a better brand part maybe CarQuest or NAPA rather than Oreilly/AZ/Advance), or you can simply remove that fuse and leave it out (but keep it in case the ECM/relay circuit stops working).

 

Thanks for the feedback.

As to the wiring, I just went through the pains of removing all the hack job re-wiring stuff from under the hood and the dash, re-wired the relay, and it DOES work properly without the fuse near the battery in. According to my schematic, it seems to be an either/or circuit from the factory. Also according to my schematic, the fuel pump should work if there is oil pressure (ie, engine running) through my fused circuit.

At any rate, it is working fine now. I am wondering if maybe the last of the old oil residue made its way out of the oil switch plug and maybe that shorted the contacts? I'm not sure but I did clean it out one more time. Its not doing it now but I will give one more extended and heated test to be sure.

I don't want to burn out my Vortec fuel pump because of a cheap oil switch.

Thanks for the input and help.

 

I had this happend last week when I put in a brand new OPSU. It turned out the Advance OPSU that I bought was bad. I put my old one back in and it fixed it.

 

Well, it seems that my oil switch is the problem as well, although it has stopped for now. I'm monitoring this situation and going with it for now.