My wife's 94 4.0L XJS would not start one afternoon. It would turn over and the
fuel pump was turning on. But would not start. I checked the Inertial Switch - OK. But there was no spark from the coil.
Swapped out the coil and Ignition module(Amp) and still no spark.
A check of the schematics showed a fuse #7 (10A) going to the Engine Management Amp/Module.
I pulled down the passenger side knee bolster to reveal the fusebox. There in the #7 Fuse position for the Ignition Amp/Module was a 5A fuse instead
of a 10A fuse. A test with a ohmmeter showed a 20K resistance rather
than the 0 Ohms expected.
I replaced the 5A fuse with the 10A fuse and the car started with no problems.
The car had this 5A fuse in place for several years. It had some odd starting problems during that time and would stall out sometimes. But, it would eventually start.
I think the fuse did not open up all the way and would allow enough current to operate the Engine Management relay sometimes and also cause the relay
to open up and "Stall" the car.