Jaguar Repair: jaguar xjs v12, jaguar xjs, fuel pump relay

Question
Hi Howard you say i now need to follow your wiring diagram from the fuel pump backwards toward the power source and the relay trigger (main relay). But im useless with electrics and dont really understand what im to do really and what im looking for ? Everything seems to now work apart from when turn key on i dont think fuel pump works but i does if i connect a live direct to it . You say about 3 vin numbers maybe it will be better if i gave you my vin number its SAJJNAEW3BB157790

Answer
That Vin number does not match any of my diagrams so the UK or Euro versions of the Vin numbers don't match the US versions.

However, they may be close so go to the fuel pump relay with the key in the "ON" position and test the pink w/black wire for power and if it does, check the orange wire from pin 85 on the fuel pump relay to see if it is grounded, and if not, ground it to see if it activates the fuel pump relay. If it does, go to the orange wire on pin 15 of the ECU and ground it there to see if you get the same result. If you do, it will be necessary to use the diagram at the ECU and test the ECU for powers and grounds and the ignition pulse signal of the ignition system when the engine is spinning. Because that proves the relays are working but the ECU is not telling the relays to work. Which requires that all the powers and grounds of the ECU must be tested and the "Start" signal and the "Ignition" signal to the ECU must be tested. The powers, grounds and "Start" signal can be tested with a test light or volt meter but you should test the ignition pulse signal with a lodgic probe. The ECU looks for a "Start" signal from the driver to start doing something and a signal from the ignition system to do something and if it don't have ALL of it's powers and grounds and those signals it, will not activate the relays to make the injectors and fuel pump start working.

If all this tests to be ok, you may need to contact your local Jaguar dealer to see what they will charge you for a diagnosis as they use to have a piece of test equipment to just plug in and test the system and in one minute can tell what is wrong. Most small shops and individuals don't have that piece of test equipment and have to do what you are doing now by testing a point at a time down the trail of electric on all the items that make it run which you already see it extensive. Some Jag dealers here don't work on the older Jags or have disposed of the old test equipment. So you need to ask what they charge for a diagnosis first.

If you get to the ECU and need to test it, you can not do that with hand tools nor test lights.
It requires the Jaguar test equipment.

Howard