Hello all,

My wiring skills are at best, primitive.
(Didn't have a very firm grip on the 20th century, and here we go with the 21st .... DAMN ...!!!)

Trying to sort out a 1990 XJ40 that's been sitting & neglected for a long time.
Got it to run briefly on starting fluid, but apparently the fuel pump isn't working.
At the connector leading to the pump itself. I get 12 volts for a nanosecond when the key is turned on, then no voltage. It will repeat this same scenario every time the key is turned on.
My question is:
Is this normal, or is it my problem rather than the pump itself?
The interaction between all the various sensors and relays is a total mystery to me.
Thanks in advance for any help.
Retro

 

The electric supply to the fuel pump is maintained only if the ECU is sure that the engine is running; if it determines it is not the fuel pump feed is cut off. So how do you start the car, you ask, as the engine is clearly NOT running ? Well the answer is that Position 3 on the ignition switch, which you turn to against a spring to start the car, bypasses this mechanism, then as the engine starts and you release the key back to Position 2, the ECU has already detected engine is running and switches the fuel pump supply, normally via a relay.

That's the theory, you just have to work through the components that are involved in the fuel pump supply. First off is the fuel pump relay, I would think.

 

Fraser,
Thanks for your response.
That all makes sense, and gives me some other things to look for. Will check voltage with ignition in "start" position .... then work from there.
Regards,
Retro