Hey everyone, I am Mitch. I recently bought a 1987 xjsc v12 cabrolet convertible. Champange exterior and interior. I drove it for a few days and it dumped on me going down the road. It is fuel related. I have replaced the fuel pump, master relay and the fuel pump relay. I have constant power to the relays and ignition power to the master, but I cannot find enough info to diagnos further. Best I can tell, there has to be a signal, or voltage from the voltage amplifier to the ecu upon ignition request, then the ecu supplies the power to make the fuel pump relay engage? Send power to the pump and injectors?

 

Hi Mitch and welcome to the forum! Come over to the XJS model section XJS - Jaguar Forums - Jaguar Enthusiasts Forum, we have a pretty good group there with a lot of knowledge about these cars.

 

The ECU sends a ground signal to the fuel pump relay to the energize the relay which in turn powers up the pump. This circuit of the SCU often fails

Ground the orange wire at the fuel pump relay. The pump should now operate whenever the key is on.

The injectors are also grounded by the ECU. They get 12v from the main relay.

Cheers
DD

 

Welcome to the forum Mitch,

Follow this link XJS - Jaguar Forums - Jaguar Enthusiasts Forum to the XJS section for help, advice and information. The 'HOW TO' thread at the top there is a good place to start for info on regular issues.

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You may also like to visit the US Southern MidWest Region section by following this link https://www.jaguarforums.com/forum/southern-midwest-ar-la-ms-ky-tn-al-67/ to find other members in your region.

Enjoy the forum.

Graham

 

Welcome to the forum Mitch,

Good to have you with us.
Enjoy the forum.

If you haven't already done so you should add your car details to your signature to help others to help you.

 

Isnt there a signal from the engine bay to the ECU from another sensor other than the voltage amplifier needed before the ECU commands ground to the relays? Maybe the coolant temp sensor or something?

Now the silly question, how do I actually ground the orange wire on the pump relay? OHM it to the body? Jump the brown wire to the orange? That would blow the fuse or fry the relay, right?

 

To operate the *fuel pump* I don't the the ECU needs anything more than the signal from the ignition amp on the #18 pin. Not 100% sure on that.

To operate the *injectors* the ECU needs input from the various sensors.

Before getting into a long discussion, can you verify/clarify that both the fuel pump AND the injectors are flat-out inoperative?




I use a test lead with a probe and simply insert it into the connector cavity associated with the orange wire...so the the probe contacts the terminal of the orange wire. The other end of the test lead is then attached/touched/connected to a known good ground point or the "-" battery post.

You can home-brew something similar



No!


Right ! Don't do that! A solid brown wire carries constant battery voltage so you don't want to connect it to any sort of ground

Cheers
DD

 

No I cant verify yet. Waiting for a day off to stop by get a tester for the the injectors. Are the fuel pump relay and the master relay supposed to be the same part number?

 

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No.

See reply in this thread

https://www.jaguarforums.com/forum/x...-wiring-91055/

Cheers
DD