Intermittent starting problem
 

Got up today, planning on taking my XKR to the annual British Car Show in Dayton. Very nice show, usually close to 400 cars. However, a problem with my car reared its ugly head. Damn thing won't start.
When the starter is engaged, the car starts momentarily, then dies. The throttle is unresponsive; if I floor it it immediately dies. Otherwise it runs for 3-5 seconds and dies.

This has been an intermittent problem for the last couple of months. My mechanic is mystified. At one point it coded that the throttle body needed work, so we replaced it with another throttle body that I got with the car. The last time, I had it towed to his shop. When he looked at it, it started and ran normally, with no codes. When it runs, it runs fine, no problems at all. This is a very nice car that I got for a good price, but it has been very frustating lately.

Anyone ever had this particular problem? Any ideas?

FUEL PUMPS more than likely..
Need to check both are running with good psi...

Fueln pumps have been checked, and have good psi.

No spark?
 

Fuel ok. Air ok. Then it’s electrical. Check voltage on dash and check if everything lights up during non-start event. If so battery is ok.

Could be ECU may have bad ground. Or bad engine ground. Change thick engine ground wire RHS from below at the Catalytic Converter. If not check if you have a spark. Bad coils?

You don't say what model year it is. The early models did have problems with the ECU that caused intermittent problems.

Finally fixed, I think
 

After being flatbedded 4(!) times to various shops, I found someone who figured my car out. I believe that the problem had to become chronic to the extent that they could finally diagnose it.
At any rate, it turned out to be the fuel pumps, which I had suspected all along. It turned out that there were half melted wires on the wiring harness inside the tank, which sounds pretty scary. They replaced both pumps, the wiring harness, and the gas guage sending unit, and it's running great now.