In the majority of the cases, general troubles which may occur on diesel engines, are due to two obvious causes :

A
Nozzle bores are stopped up AND the nozzle drips
B
Compression is too low AND exhaust valves leak
C
Delivery valve leaks AND piston rings are burnt-in
D
Diesel engine refuses to start AND diesel engine supplies too little power
E
Regulating rod sticks and injection plunger is damaged