Jaguar xj6 not starting

Dirty throttle body and relurn after cleaning , fuel filter , air filter, fuel pump ?

Try gently moving the shifter around while cranking the engine (while in the park position). There is a sensor in the J-shift that will prevent the proper voltage from reaching the main computer if it is out of adjustment. This problem drove me nuts until I figured it out. I would start and run fine, then it was like the fuel pump went out. Good Luck (I know it's an old post but it might help someone)

I have had simmilar, is the fuel pump delivering fuel?
Is the fuel filter clean?
Are you getting a good spark on all of the plugs?
Have you got good cyl compression?

Possibile ignition control module problem Check for spark when problem occurs No spark.. Follow wires from distributor to icm box. Open box and you will find a gerneral motors ignition module. Remove module and have tested at local parts store. Replace if bad. Jaguar wants over $300.00 for IGNITION AMPLIFIER UNIT. You should get gm module for under 50 bucks.

check your flowmeter, this electronic device moniters air/fuel mixture, commonly located on the inlet manifold near injectors

check the injectors nozzle also check its resistance by using a multimeter also check the coming voltage for the injector which is 12 volt.

Timing out ,check it on no1 cylinder at TDC then check distributor position ,the arm is pointing at no1 plug lead

does it have a spark at the spark plug leads? if no it sounds like the crank shaft sensor!!

Does it even try. (cough and sput) Will it start if you spray carb cleaner in it?

Not sure if it would be the same problem, but I had a 1986 xj6 that was acting up a few years ago, and it turned out to be that the fuel injectors where not working right. On mine, there was a box in the lower right front the was like a control box for the injectors, and the circuit board started to corrode and make intermittent problems with starting and running. Sorry I could not be more detailed... Good luck.