I have a 99 XJR with 84,000 miles. I have replaced both fuel pumps, camshaft, and crankshaft sensors. The car will run for 5 seconds and then stall out. I disconnected the battery and tied the positive and negative cable ends together for 20min then reconnected them. Still having the same trouble. Anyone have experience with the computers on these cars, I have been told that may be my problem. Can they be reprogrammed ? Or just replaced? Can used ones be programmed to the car? Is that a dealership thing???

 

It sounds like you are throwing parts at it. Have you checked the fuel pressure during the start/ fail operation? A clogged fuel filter could be at fault. What about codes? We really need more information.

In the unlikely event your ECM does need to be repaired, the are companies that will test and rebuild yours, reprogramming is not required then. Here is one of them:

Automotive Scientific Inc. Your #1 Source for ECU, TCU, ABS, EBCM, Climate Control and Speedometer Repairs

 

I replaced the fuel filter when I did the pumps, then after I started it is when the codes came up, p1000 and p1336 P1000 is because the test was not complete. P1336 is cam/crankshaft. So I replaced both of those sensors. I'm stumped!! By what the problem is, the vehicle was running just fine until the no start happened. Stopped at the store went inside for an hour came back out and no start Anyone have any advice!! I'm two steps away from having the car hauled to a jag dealer!! Do not want to, but am running out of options.

 

This does not sound like an ECU problem. I would bet that something was not installed correctly when you changed out the fuel pumps. You need to check the fuel pressure at the rail. are the connectors to the sensors tight and corrosion free?