Hopefully I've found the correct forum as I've recently inherited this car and am not that familiar with the models.
Fuel pump works, I have power to the fuel pump relay. If I jump the relay the pump works. However the pump does not work when I turn the key on and try and start the car. ???
Any idea's.

 

So there you are

I will be editing this post while I watch the Chiefs

See the 91 wiring guide on page 71 for the fuel pump relay that relies on the main relay

See this link post # 2 with the wiring guide download in red letters

https://www.jaguarforums.com/forum/x...oblems-221924/

We will be splitting the relay in half to understand

One half is the control side and the other half is the power contact side


You were jumpering across socket 30 and 87 to directly power the pump and this is the power contact half

But to control the relay power in the form of control power is sitting on socket 86 and a ground at 85 to close the relay is provided by the ECU , this is a ground seeking relay

This control power is from the power contact half of the main relay

You have a fuse for this main relay and you should feel for it to click closed anyway

Fuse C1 / 15 amp left fuse panel

This is point 27 square on page 71 top left side and back on page 11

Finished editing

 

Thank you so much for such a nice detailed reply. I'll be back working on the car tomorrow.

 

Easyest thing would be to swap relays but not between the 2 suspect

Maybe a headlight or simular with the same part #

 

Ok, both the fuel pump and air pump relays test good. Here’s what I now have. With the fuel pump removed from the car when I turn on the key the fuel pump now runs for a couple seconds and then shuts off. Should it continue to run as it’s not seeing any pressure?

 

I'm going to say something about how the fuel pump works on the later model X300 that may or may not pertain to the XJ40

The fact that you had it running for the 4 seconds is a plus

I feel the need for some tacos

Upon key rotation the ECU provides a ground to close the fuel pump relay for 3 - 4 seconds then off when it removes the ground

This primes the fuel rail with pressure that is trapped by the check valve in the fuel pump and the not opening of the fuel injectors and the fuel pressure regulator failing open or leaking through the rubber diaphram

The check valve can be replaced by a external fuel line ckeck valve or pump replacement or a stuck open fuel injector

But we will go forward before concerning replacing any parts

Once the engine is spinning the crankshaft position sensor sees engine rotation and triggers the ECU to agian provide a ground on the same wire to the FP relay to close for the duration of your drive

You can have failure in not getting this FP relay clicking 3 times on . off . on

Or falure to obtain combustion in the transition period before the fuel pump turns back on with the 3rd click

The starter rotation speed is 300 RPMs and the 3rd click of the FP relay may be higher then that

You can have failure in the CKPS in it's use as the fuel pump enable but still give you tachometer indication and ignition / injector timing or maybe ignition / fuel injector timing

In your case you have mechanical ignition timing with a distributor cap and the X300 is purely timed from the ECU and does not have a distributor cap

Looking for relay that controls injectors

Where you able to start the engine with the fuel pump relay jumpered ?

The trapped fuel pressure in the fuel rail will hold for days and can be checked by cracking the fuel rail lines fitting at a certain point at the fuel pressure regulator

Be careful to not twist the fuel rail so use 2 wrenches

 

Ok, good news I think. Bought a new fuel pump and hooked it up. It runs for a couple seconds when I turn the key on and then when I crank the motor it runs while cranking. So I'm pretty sure the pump is doing what its supposed to.

 

Ok so now we are at a new information package from what you observed

As the fuel pump motor fails it will pit the internal power contacts in the FP relay

It will also burn the sockets on the fuel pump itself connector

This will compromise and limit the current to properly drive a new fuel pump

If you had the V12 you have 2 fuel pumps to play with

 

Good news. I buttoned it up with the new fuel pump and she fired right up. Ran her about 20 miles and so far all good. Now I just need to reset the check engine light. Its showing Fuel 22 code. which appears to be a, you guessed it. Fuel pump.

I have an OBD tool so hopefully I can use that to clear the code so I can have the car smog checked. Good old California.

 

You can quickly clear the code by disconnecting the battery, no OBD2 tool will plug in to this car and certainly wouldn't be able to clear any code!
There are other ways to clear codes without disconnecting the negative terminal of the battery, but that is the most straightforward.

Larry