TBI-to-CARB just trying to understand the fuel pump relay - Third Generation F-Body Message Boards

Token · 06-01-2005, 02:26 AM

I'm looking at this thing like a cat watches you in the shower. I understand schematics no problem.

The orange wire has +12v at all times. This connects to the ECM, the relay, and the oil pressure switch. The gray wire connects to the fuel pump (which is grounded) and has two chances to get power; one from the fuel pump relay (which is only activated by the ECM) and the oil pressure switch.

Please explain to me why the oil pressure switch does not complete the circuit on its own. I was under the impression that after 5psi, the oil pressure switch would trigger "on" giving the fuel pump it's needed voltage, thus once the car is running the pump will activate itself from this switch.

Right now I have my pump wired to the ignition from the distributor power wire. I just gave the gray wire 12v. I want to do this the right way, and I've read everything else. Everyone just says to wire it to the oil pressure switch- well it IS! It came like that stock! So why isn't it working the way I thought it is supposed to?

Also, approximately what RPM is enough to cause the oil pressure switch to turn on? will it come on during cranking, or is there a need for a momentary "prime" switch? I did notice something, however. My car would not turn off when I turned the key off the first few times. I had to remove the ECM fuse (it was the first thing I checked when this happened) to shut the thing off. This means it was getting power to the distributor (probably from my wiring the fuel pump to the distributor... seems to me like oil pressure switch completed the circuit, which fed through to the distributor still... lol)

Token · 06-01-2005, 07:03 PM

You know, I never checked to see if my oil switch was working... I might as well jsut replace it.

vrtc350 · 06-01-2005, 08:38 PM

You don't have a better copy of that image do you. I'm doing the exact same thing right now. The 305 is completely out and now I getting ready to start with sorting out the wiring. What pressure regulator are you using? I found one made by Holley for $25. Just curious.

Token · 06-01-2005, 08:48 PM

Quote:

Originally posted by vrtc350
You don't have a better copy of that image do you. I'm doing the exact same thing right now. The 305 is completely out and now I getting ready to start with sorting out the wiring. What pressure regulator are you using? I found one made by Holley for $25. Just curious.

I'm using the $70 mallory one... Actually more like $80 after buying all of the fittings I needed

Oh well, I'm satisfied.

the picture is taken with a digital camera, thats why it's crappy. From left to right goes the relay, the oil pressure switch, and the fuel pump.