UK Car Repair: Jaguar XJ6 Gold 1994 3.2 auto petrol, crankshaft position sensor, key fobs

Question
Dear William, I'm at the end of my tether after buying this beautiful but unreliable car. I have an intermittant starting problem. The car  starts first time when left over night, but refuses to start 8 times out of ten when warm. It fires, turns over and even runs for a few seconds before the revs die and the car cuts out. Hitting the throttle makes it die quicker. Sometimes it just turns over without firing. I can sometimes get it to start by opening the door locking it with the key then opening it with the key again (but that doesn't always work). Using the fob (security system) seems to make things worse. I have replaced the coolant tempreture sensor, and the crankshaft position sensor to no avail!The batteries in the key fobs are ok. I can't find a mechanic who has a clue what to do next! Please help, I'm fed up getting stranded for hours.

Kind regards

Chris Smith
Classical Composer (Hopeless mechanic!)

Answer
This is a difficult question.  The fault has to be traced as it occurs.  In other words, when it doesn't start it must be checked to see if it has a spark and fuel pressure, obviously if it is missing one you can then focus on that system, if it has neither, is is a computer problem