the fuse is between the pump (displayed as M on the diagram) and the relay/pressure switch section. The red from the battery turns to orange, then orange is a split 12V for BOTH the relay and the pressure switch, when the relay is switched or the pressure switch is activated they energize the 12V on the tan/white wire and THAT wire is fused and goes to the pump. All the way to the fuse box it's tan white but from the fuse box to the rear conenctor at the tank it's blue, why? So that no 2 tan wires run in the same wiring harness where 1 is a feed from relay/pressure switch to the fuse and the other back to the pump. That would be quite confusing if you needed to find otu which of the 2 was the "from" and which was the "to"
So, this means that there is NEVER 12V at the fuse if:
- the relay does not switch on
- the pressure switch doesn't switch on

The relay ONLY switches on for a couple of seconds after the ignition is turned on. It's timed by the ECM so the ECM powers the relay on and off, it's to prime the fuel system for proper pressure. If you turn the ign. on but don't start the engine the pump will cut out. Turning the ign. off and back on again won't necesarily prime the pump again, there's a timer and if the interval between the 2 actions of ign. on is too short the pump won't prime again. I don't know what the interval is, never clocked it but it should be something in the order of 30-60 secs.

The pressure switch only switches when the minimum pressure setting is met, I think it's around 10psi but I could be wrong (never relly checked it) So, when you don't crank the engine it won't switch the pressure switch on so when testing w/ the ign. on you will only see 12V at the fuse for as long as the relay primes the pump. If it never primes the relay is either shot or not being actuated by the ecm..or there's a wiring problem.
If the relay does prime the pump and the car still won't start and/or keep running then it's the pressur switch msot likely, if there's a proper 12V and the pump will never run then it's the wiring, the fuse or the pump itself.

The green white is the fuel pump drive.

Since your car started it means the pump is good. After it started try taking away the 12V that you bypassed directly to the pump, if it keeps running the 12V is being supplied by the pressure switch and that is fine also. If not it's very unlikely that both the relay and the switch are bad, which must mean there's a seriosu problem w/ the 12V Feed. Probe the tan white wire at the press switch for a 12V source (which is there constantly - it's ignition switched) and the same for the relay. If there's no power on either (they come from a shared wire, a split connection) then check the connection to the red battery wire, I'm not 100% psoitive where that one is but I suspect it's in the main harness under the console or the engine harness pulling directly from the alternator to battery wire, I could check for you but only as early as next friday. I have the entire wiring harness in a box.

If there IS power to both then it can mean only 1 thing..there's a wiring problem and it can be either the connector or the fuse box itself.

 

Yes, once I take away the 12V I bypassed directly to the fuel pump fuse, the car shuts off.

Based on all the information given, I suspect my problem is between the harness where the relay and the oil pressure switch meet and the fuse. I guess my next step is to check the continuity of tan/wht cable from the relay to fuse and from the oil pressure switch and the fuse.

Twin_Turbo, if you can get me the location of where the tan/wht cable from the pressure switch and the tan/wht cable from the relay meet, that would be very helpful. Since its back to work tomorrow, I can wait for you to check the harness next Friday.

 

Is your oil pressure sensor good? Your car won't start if it isn't. Regardless....if Twin turbo can't figure out no one can...

Keep us posted on progress. It may be a problem I have some day.

Jim

 

I don't know where the junction is, sorry. If you really need to run the car, pull a wire from the ign. switched terminal (there's an open one down left on the fusebox) and run it to a switch, then run that (w/ a 10 amp fuse) to the pump, that way you can manually turn the pump on and off and still run the car (it will go on/off w/ ign. but you can use the switch to turn the pump off if you want to trouble shoot it and need the ign. to be on)

 

My '82 once had a hard time starting, I would crank it for a couple minutes sometimes before it would fire up, turned out to be the fuel pump relay, it had some black goo on the contacts, where the goo came from is still a mistery, it wasn't on any other parts, just the FP relay. I cleaned it off the it worked, but I replaced the relay anyway just to be safe since I had everything apart and it's such a pain to get at it.
P.S. your best advice comes from TwinTurbo, he's the guru, helped me on several occasions.

 

Well I had some free time today to continue troubleshooting my problem and amazingly, the car started. Now I dont know what the problem was. I am afraid of driving the car and leaving me stranded somewhere, but I guess this is part of owning such a car. Anyway, thanks for all your help and advice.

 

start and let it warm up and go for a drive around the block,,or as far as you want to walk and see whats up