HI-

I recently purchased a non running 1989 XJS V12 on a whim Always liked the cars- The car would not start and the previous opwner said he thought it was ignition oe fuel pump related-
So first i wanted to check and see if i was getting fire- Good spark at both the coil and off one of the cap terminals- I could not verify if i was hering the fuel pump prime so i just removed the pump- Supplied 12v and it ran fine- I could not get 12V to wires connecting to the pump so i replaced the relay and still did not see 12V and could not hear it prime (the car is parked by a busy road so i may not be hearing it). So rather than continue troubleshooting that i jumped ahead and bypassed the relay and ran the pump off 12V- Checked up front and i had fuel to the injectors- So now i have fuel and spark and it fired right up? NOPE- Did not even try to start- So i twisted the throttle capstan and can hear no click of the injectors- So i removed the EFI resistor pack and cleaned the terminals and while i had it out and disconnected i checked the harness side of the plug for power and with the car in the ON position i did not have 12V to any of the terminals- I also checked 2 injectors and with the car in the ON position do not have 12V to either- Also behind the capstan when opened it completes a circuit via a mechanical connector- I do not have 12V to either side of that at any point- So basically I have spark and fuel to the injectors but nothing getting past them into the cylinders-

Are any of these power issues related? Do they have/not have power at certain times and I am mis-diagnosing?

Amy tips or where to check next would be a huge help!

Thanks
Gabe

 

The 12 volt supply to the injectors comes from the "main relay" which is in the trunk/boot. The relay may have failed

I'd make a few quick wiring checks......

The solid brown wire at the relay should be 12v "+" at all times. The white wire should be 12v "+" with the key on. The black wire is ground. The pink/black wires are output to the injectors and should be 12v "+" with the key on.

We might well have to dig deeper but as a jumping-off point (ya gotta start somewhere, right?) , this ^^^^ is where I'd begin

Note that if the relay has failed it must be replaced with one having an internal diode.

Cheers
DD

 

I might add that the "main relay" also powers-up the ECU itself and provides voltage to the control side of the fuel pump relay

Cheers
DD

 

Doug-

Thank you so much- This sounds like it could be the ticket- The relay i replaced was fuel pump rather than the main relay- It sounds like all of my power issues are all common in the fact they originate from this relay...

Quick question- The relay with the internal diode may not be something my local autozone carries- Is there a temporary workaround to test it if i have to order the part online? Also off hand do you have the part# for the relay with the diode handy? The car is sitting in a parking lot down the road so i cant just walk out and check myself

Thanks Again

 

If you have 12v "+" output on the pink/black wires with the key "on" then the relay is OK. if not, check the other wires as noted

The original part number was AGU1070 which is no longer available from Jaguar. Search the archives under that part number for discussion on replacements. Some vendors are selling an incorrect part

Gotta run ! Chores to do !

Cheers
DD

 

Doug-

I owe you a beer my friend- Ran over there and swapped out the main relay with the old fuel relay i had swapped earlier today and it fired right up and i drove it home... Man I owe you

I will get the correct relay ordered asap-

 

Glad you're sorted ! I only wish they were all that easy

Cheers
DD

 

No kidding my issues are similar and I have a click back there to when I turn key so I'mma go inspect!!!!good info btw,

Corey