1999 XK8. Normally runs fine no issues. I can drive it to work and then home at the end of the day, no problem. However, after the engine is warmed up it will refuse to restart if I stop somewhere briefly, like running to the grocery store. The engine will try to start and appear to start but only for a half second and then it will immediately die. It will do this repeatedly, like it is getting one shot of gas from the fuel injection and once that burns that's it, literally a half second. I can do that over and over with no success. If I let the car sit for 20-30 minutes it will start right up as though nothing is wrong. It is difficult to predict when this might happen. However, it does seem to happen on the warmer days. Typically I only drive it to work and back, so the frequency of occurrence is low; it only happens when I try to restart after the car is warmed up. I checked for thrown codes but there aren't any. Any assistance appreciated.

 

Check your fuel pressure at the rail, look for 35-40 pounds. See how fast it leaks down after a shut off, should be very slow. It might be time for a new fuel pressure regulator, too, easy 5 minute installation.

If there are codes, let us know...

 

This is the location of the Fuel Pressure Test Port at the rear of the right side Fuel Rail:

 

A few things, a leaking or dirty injector, a failing fuel pump check valve allowing a bubble to develop in the fuel line. Either one of these would not be unusual in a car this age. Try some good quality fuel system cleaner to start with.

 

Responding to the two suggestions: