Worn out crank and cam shaft bearing
Defective injector
Weak compression
Defective battery
Piston ring wornout
Defective oil relief valve
Loose fan belt
Defective alternator
Defective pressure gauge
Improper valve timing
Excessive valve guide clearance
Clogged fuel filter
Defective pressure relief valve
Fuel filter clogged
Worn out liner
Fuel leakage
External leakage of oil
Defective thermostat valve