Jumper the Oil pressure unit

[TMRuddy]

Hi all -

I'm trying to help my husband diagnose our fuel pump not turning on and a common reason seems to be the oil pressure sending unit. I see that if I jumper wire it we can tell if that is the issue. However, not sure how to do that?

Any help would be GREATLY appreciated!

Thanks!
Tina

P.S. We have a 77 Vega Hatchback. Just got the car and looks to be 98% original. Just installed a new fuel pump, so the pump "should" work, but we are not getting power to it.

[monzaaddict]

Another thing to check is the ground wire in the tank. That is that flat black cable that goes from the pump up to the terminal where the wiring harness connects. Twice on cars my family owned there was corrosion between the cable and the terminal it connects to. That little clip has to be removed and the cable and terminal cleaned. There is a plastic insulator that breaks easily between the terminal and the flange it attaches to where the fuel pump assembly attaches to the gas tank. I remember my brother banging on the bottom of the fuel tank to get the pump running so he could get to work. The pump intermittently worked after replacement and cleaning the ground cured the problem.

check the fuse too.

pull the harness off the fuel pump and see if there is power to the pump.

[TMRuddy]

Fuse is good, but no power going to that fuse location. Rest of the panel has power.

We'll check on that clip.

Thanks!

[cjbiagi]

The way GM had them wired is still just about the best way to power a fuel pump. The original plug had pink(ignition), violet(starter) and blue(pump+) wires. at rest(0psi.) the blue is connected to the start wire so it will power the pump while cranking for initial start up. When there is oil pressure(minimum 10lbs., I think) the pink is connected to the blue taking over from the starter. This is a fail-safe method so that in the event of a crash(or stalled engine), the pump will be off. Most fuel injected vehicles are wired like his now, showing once again the Vega was ahead of it's time! This is much safer than just running ignition power to the pump- which is what you'll have to do to get this thing running. For now, find the pink in the harness and splice it into the blue.

[stage169]

If you don't want to turn the engine over to see if the fuel pump will run REMOVE the connector to the oil pressure switch.

Then get positive 12 volts to the blue wire and the fuel pump should run. Just make sure you REMOVE the connector on the oil pressure switch or the engine will turn over when you put power to the blue wire!!!

Not sure about the 77 Vega Hatchback but on my 77 Skyhawk there is a connector for the fuel pump at the back. The wires come up from the tank and then go to the connector inside the car. If you DISCONNECT it there you can access the blue wire. Don't jump power to the blue wire with the connector made or the engine will turn over!!!

Might be a good idea to use a fused jumper wire, if you do it from the oil pressure switch connector at least it will go through the fuse box before the pump. But a fused jumper wire will give you protection in case there is a problem from the oil pressure switch to the fuse box. If you jumper power to the back connector your fused jumper wire is the only protection. The fuel pump has a 10 amp fuse.

Brian

[cosvega76]

Tina,

An easy way to check the pump is to make a jumper wire, about 2" long, with a male spade connector at each end. Pull off the connector to the oil pressure switch and jumper the two parallel connectors in the plug. The pump will be energized whenever the key is in the ON position. The trouble I had with my Vega's fuel pump turned out to be loose connections in that oil pressure switch plug. I used pliers to squeeze the female spades in the plug slightly so they made better contact with the switch terminals. You can use your jumper wire to check the snugness of the fit.

There's some more fuel pump/oil light wiring discussion in this thread:
viewtopic.php?f=44&t=41060


Chuck