Jonathan Dyer

iTrader: (5)

I changed my clutch yesterday and all of a sudden the fuse for the fuel pump blows when I turn the starter.

At the fuel pump relay there is one wire which has constant power with or without the fuse. There is another wire that runs to the to the oil pressure switch - the other side of the switch grounds to the firewall - this has power with the key on. A third wire goes directly to the fuel pump and a forth thinner wire disappears through the firewall somewhere below the master cylinder this maybe goes to the fuse box or the ECM?. The forth wire also has power with the key in the run position.

With a fresh fuse and the key "on" all but the fuel pump wire have power. Once I crank the starter though the fuse blows in the fuse block and I only have power to the one that has constant power with the key off.

If these wires were shorting the fuse would blow as soon as I turned the key to the run position. so I reasoned that when the relay sends power to the fuel pump that's when the short occurs.

I snipped the wire going from the fuel pump relay to the fuel pump put in a fresh fuse and turned the key to "on". Power everwhere it should be. but when I cranked the starter the fuse blew.

I'm stumped....

Thanks,
Jon

JSD MOD 06/03/09

Jonathan Dyer

iTrader: (5)

Alright, so the wiring has all been hacked at some point. None of the wire colours match the manual. The keyed power to the fuel pump relay is from the fuse box (fuse for the wipers). I noticed that the wiring for my reverse lockout ( I have a T56 trans.) was nicked during removal or installation of the transmission. That was temporarily plugged straight into the fuse box with a spade connector so it wasn't fused. It was on a completely different circuit though...At any rate the wiper motor fuse no longer blows when I crank the engine.

The fuel pump has not run yet but it usually doesn't prime unless I try to start the car and fail. Then the pump runs for 4 seconds and stops. I have been cranking the engine with the distributer trigger unplugged because it's after 3:00 AM and I have open headers. So, I'll have to wait until tomorrow to see if the fuel pump comes on.

I'm still confused though. The ECM is what runs the fuel pump to prime the carb (or more probably the car was originally equipped with a TBI) and shuts the fuel pump down if there is no signal from the oil pressure switch right? But three of the four wires to the relay are accounted for (power to fuel pump, keyed power, power to oil pressure switch) and the forth has a constant 12V. How is the ECM connected here?

Thanks,
Jon

deadbird

Do you know what motor was in the car originally ?
The only FI I can think of offhand for 83 was crossfire and the 'el iron dookie.

What is residing in the engine bay now ? Do you have a regular carb'd engine and the original ECM as well ?

BigBadLou

iTrader: (3)

I replied in your oil pressure thread.

You refer to TBI so let me just slap a diagram here for you to look at if it matches your wiring:
http://www.austinthirdgen.org/mkport...ta_sensors.jpg

Hope it helps.
Lou

Jonathan Dyer

iTrader: (5)

Yes, it's carbed now.Maybe it always was. The ECM is still functional although not doing much. I just figured that the ECM would be the only thing that would run the fuel pump for it's priming cycle.

Jon

deadbird

I kind of had a feeling you were going to say that. It sounds as though the previous owner was trying to make the OPS run the fuel pump in a different way.

See if this post helps you out...

https://www.thirdgen.org/forums/elec...fuel-pump.html

Jonathan Dyer

iTrader: (5)

I just wanted to thank DeadBird for responding and BigBadLou for taking the time to post that schematic. In the end, it all works fine once I unplugged the wire for the reverse lockout.
Thanks again,
Jon