Oil Pressure Switch Disbaling Fuel Pump

[Brin]

Good evening fellow commodore drivers.....

Problem: Last night the trusty VN stalled and left us stranded at a servo. Oil light came on, could not hear the fuel pump prime, it was blowing fuses and every time we tried to crank her over, oil spluttered all over my recently degreased bay from the switch. Grr.

Waited for NRMA fella who was pointless and unhelpful. I explained the problem and he looked at the bay and said "thats red oil... your power steering" He was adament of it without even starting the car so I cranked it over to show him where it was coming from and she shut up quickly. He did not even look at the fuel pump, fuses or relay, didn't even give the tank a good bung or anything.. When I asked what to do in regard to that he just said if it was blowing fuses to replace the pump. I got his rego and plan to complain. That was my last "free" callout and he was the most unpleasant and uncaring fella I have come across yet. Oh, he also added that i'd cop a hefty cleaning fee if his guy towed me coz i'd leak oil all over his tray. Heavn forbid, NOT THE TRAY!!!

Four hours later, we were towed home for $100. Towing is expensive. I'm getting used to seeing the old girl on the back of a truck now.. lol.

Checked relays, fuses and pump for power. Nothing. Started at the easiest spot and replaced oil pressure switch. Oil light went away instantly. Checked relays etc again and had power.... Fuel pump primed and what we though was going to be a dreaded job we would send to the auto elect was that easy..

My qu is though, how does the oil pressure switch affect the fuel pump relay?
My understanding is that is so if the pressure drops, the engine will cut out intead of siezing..

My car starts without the fuel pump relay so im assuming that is effed..
As long as the 15 fuse is in, does not matter about the relay, she sends fuel..... In my thinking, if my relay is dodgy, is it my oil pressure switch thats running the fuel pump completely?

Also, the oil pressure switch used was an old one in the garage from a VC or VH...... =\ It's working, oil isn't going everywhere or leaking, theres no lights on the dash, but how long will this hold? Or continue working, as this one does not have the same sensor/plug on top.

Sorry about the journal... Haha...

Thankyou for reading, and your replies of knowledge are appreciated! haha

[SweetWagon]

The fuel pump relay primes the fuel pump when first turned to ignition, Once the car starts ie. (oil pressure) the pump draws power through the switch AND relay, so yes the car will run without the relay once started, It is possible it will start without the relay if theres enough pressure in the lines...they both share fuse 21 (15amp) so it wont run without that.

Also the car will continue to run with low oil pressure, It simply signals the oil pressure light, both fuel pump and motor will continue running.

Cheers

[Brin]

I get ya butttt, my car STARTS AND RUNS without the relay.. All it needs is the 15amp fuse.

The relay is just there for show, hehe

[SweetWagon]

I get ya butttt, my car STARTS AND RUNS without the relay.. All it needs is the 15amp fuse.

The relay is just there for show, hehe

I'm guessing that's only because of pressure left in the lines. Might not start if you left it overnight without relay as the pump does not prime without the relay.

[Cheap6]

The fuel pump relay primes the fuel pump when first turned to ignition, Once the car starts ie. (oil pressure) the pump draws power through the switch AND relay, so yes the car will run without the relay once started, It is possible it will start without the relay if theres enough pressure in the lines...they both share fuse 21 (15amp) so it wont run without that.

That might have been better expressed as "...the pump draws power through the switch AND/OR relay...".

If the oil pressure switch works, the pump will be powered whenever oil pressure is present. It's normal to be able to remove the relay and the car will still start (after extra cranking time required to generate oil pressure) and run. It sounds like the old switch was shorting to earth. Not 100% sure if the 'new' switch will be a permanent fix but V6 oil pressure will be similar to VC or VH so I doubt that will be an issue. If it was my car and the electrical connection was good and not just 'twist and tape' I'd leave it and save the money otherwise spent on a new VN switch.

I have never seen what I would consider a definitive reason for using both the ECM switched relay and oil pressure switch to control the fuel pump. There is a connection to the ALDL diagnostic connector so it may have something to do with the diagnostic tool.