P38, Cutting out on overrun/slowing down.

Hi, Please help me I have a P38 1997, 2.5 Diesel Auto. When slowing down the injection light comes on and it cuts out, only when hot. Has hot start device fitted, will not restart when hot. But works great when its cold.
Its getting that we don't want to go out in it.
Also can you explain to me simply what the electronics on injector No 4 do and how to test it.
Many thanks Pixie

Sensor or #4 is start of injection sensor, RAVE explains it better than me in diesel injection chapter. Best tested on Testbook. About £140 to buy. Can replace DIY (if you handy and have correct spanners). If you do replace it change the small hose at rear of block under air manifold: costs coupla quid , but pain to get to! From your description could well be worn that or FIP; costs more to replace and not as easy either. FIP tend to go at 130k or above.

Faultmate or Testbook can be used to diagnose injector 4 problems. It is also used in conjunction with the crank sensor to determine engine revs, if the crank sensor fails, it will still run but stall on the overrun as no fuel is being injected so no signal from injector 4. First check must be crank sensor.