Hello,
I had a question regarding the fuel pump voltage during cranking. I've been experiencing 4-5v during cranking and also 4-5v when putting the key into ignition. What is the proper value that I should be seeing?

Jason

 

you should have battery voltage. If you're getting only 4-5V. Rewire your fuel pump.

-AzEKnightz

 

Thanks! I just did the rewire and hopefully it'll work!

 

HI there,

I think rewiring the pump - while a solution, does not look to get at the heart of the problem.

Firsty, are you checking the voltage at the pump/tank?
Secondly - have you checked the voltage going into the fuel pump aka circuit opening? I would start there as if you have an issue there, a rewire will not work.

The circuit opening relay feeds 12V to the fuel pump (via the fuel pump resister and another relay, fuel pump 'speed' - depending on load and engine speed.

See page z28 for the circuit diagram

http://wright-here.net/files/manuals...%20diagram.pdf


The fuel pumps 12V source comes from a thick blue wire that comes from the engine loom out of the 20 Amp fuel pump fuse. Have a look at the big relay box beside the battery - if you can't see it, just pull the circuit opening relay (yes it does comes and takes some wiggling from side to side). Check with a mulimeter with the key on for a 12 V and make sure its the thick blue wire. If that checks out ok - then thats eliminated that.

So, you can now 'jump' the terminals in the relay box (again I am assuming you have basic electrical knowledge. You need to feed the 12V from the thick blue wire to the blue wire with a red tracer. Now - go check the pump voltage - Same?

The other source is the fuel pump resister - you will need to test the voltage out of this (the thick white wire with red tracer). You can test the continuity of the FPR too - should be -.57 - 0.7 Ohms.

The earth side of the rekay could be bad too. Its a very light gauge wire, that earths the relay through the diagnostic port....but, lets see if the other things bring up any issues first.

So - a few things to try there first to see if you can find the source of the problem.

All the best - Rusty

 

Sorry for bumping an old thread,

The FD I'm working on (94) is having fuel problems. The white wire at the fuel pump shows 0v when it's keyed on. I can only get it to start and get 12v when I jump F/P to GND in the diagnostics box. I've tried changing out both relays and the resistor for different used ones. Is it a bad ground in the diagnostics box like you were saying?

 

When you first turn on the ignition but stop there instead of cranking, the ECU only turns on the FP for a second and then turns it off. Read the FSM section "F" all about it.

For testing as per section "F", you have to go to the diagnostic box and connect between terminals F/P and GRND.

 

I was on the phone with someone else helping me troubleshoot. Turns out that one of the blue (resistor?) in the ecu was all brown. There was no continuity on each side so I got another one. Hopefully this will fix it. Have yet to try it out.