1990 not running

I am new to the group. Someone recently gave me a 1990 with 66k miles, that sat a very long time. It will not run. I pumped and flused the tank. The fuel pump does not run but it does if i jump the relay connectors pins. I have fresh fuel up to the requlator but not out of it. I have no pulse at the injectors. I cleaned everythig related to the injectors that i can find. I have spark at the plugs and if when i squirt fuel into the intake it fires right up. I turn the key on and open the throttle but no pulse with a noid light. What else shouldI test. I have a fuel requlator and fuel pump relay on the way.

Welcome to Jag-Lovers!
Your 1990 XJ-S likely has the 5.3L V12 with the Marelli digital ignition system and Bosch/Lucas electronic fuel injection system. There is a Crankshaft Position Sensor (CPS) located at the front of the engine beneath the harmonic balancer that provides the critical signal of when to fire the fuel injectors. One possibility is that the CPS has failed and without that signal the EFI ECU won’t fire the fuel injectors. The Jaguar XJ-S Repair Operations Manual (ROM) has detailed instructions of how to test the CPS with an oscilloscope if you have one available. If you don’t have an oscilloscope available then your best bet would be to remove and replace the CPS. This is a common failure mode for these cars as they age and/or sit. The Jaguar part number for the CPS is DBC12507. If you are in the USA Jaguar parts suppliers like Moss Motors, Welsh Enterprises, and SNG Barratt will likely carry them for about $100 but local auto parts stores may be able to get one for you. You will probably find them for sale on eBay as well.
BTW, pretty much everything that can be discussed about these cars has been many times over and is in the archives. If you search the Jag-Lovers archives for “crankshaft position sensor” or even “CPS” you will find dozens of posts from others that had similar no start problems with their V12/Marelli/Bosch cars and how they fixed it.


Thanks for the prompt response. I read some where that if the CPS had failed that I would noy be getting getting spark from the coil. Would like to verify before tackling it. Any info on how to replace it. Look like it is near the crank. THANKS!

The EFI and ignition systems in these cars are pretty complex and have a lot of sensors, relays, wiring harnesses, and other components that can have failed. There are many possibilities for what could be causing your no-start problem, the CPS failure is a common one. Another common one is the failure of the small shielded wire that communicates between the Marelli ECU and EFI ECU. With a break in that wire, or contact between the inner conductor and the shield you probably would have spark, but no fuel injector firing. Perhaps that is your problem?
I have found that having good hard copies of the Jaguar XJ-S Repair Operations Manual (ROM) for detailed repair and servicing instructions, the Jaguar XJ-S Parts Catalogue for parts illustrations and part numbers, and the S-57 Electrical Guide for all the wiring information have helped me work through many complex electrical issues in our 1990 XJ-S convertible.
The CPS is located beneath the harmonic balancer at the front of the engine. It’s been a while since I removed and replaced mine, but the harness snakes up the front of the engine and the connector is up beneath the A/C compressor on the left side. It is not easy to remove the old one, or snake the new on up and reinstall the clamps. The ROM, S-57 and Parts Catalogue were all helpful to me when I removed and replaced mine.


It is looking like the CPS. Found and cleaned connector and can source a new one for 100 dollars. I am getting close. Thanks!


It’s controlled by the ECU, although independent from the injector circuit.
Unless the relay or it’s wiring is bad, you might need a new ECU as well.

After more research, I will try a new Main Relay. Thank

In a message dated 9/7/2023 6:17:56 AM Central Daylight Time, noreply@jag-lovers.com writes:

The Main Relay is Jaguar part number AGU1070. There are a lot of relays in an XJ-S that look alike from the outside but are very different on the inside and work differently. The Fuel Pump Relay is part number AGU1068, it sits next to the Main Relay and can look similar. It is possible that whoever had this car before you installed incorrect relays or swapped the relays around into incorrect positions in error while working on the car.


After reading old post and due to getting spark , I thought it might be the main relay. Found a used one on ebay for 10 dollars. Installed it, injectors are now pulsing and fuel pump is working as it should. Getting close