Diesel fuel injection engine diagnostics, Diesel Mechanic : Servicing & specialist repairs:
Breakdown mobile technician callout available to Shrewsbury, Telford Shropshire areas
(subject to service van availability). Enquiries welcome.

Possible Diesel Engine Faults

Possible Cause
Engine will not start  
Low battery voltage.

Starter motor or related wiring fault.

Engine immobiliser locked.

No fuel in the tank.

Incorrect fuel in the tank.

Fuel supply line blocked or primer pump inoperative.

Air entering fuel system.

Pre heater (glow) plugs / relay / wiring faulty.

Incorrect valve timing.

Incorrect Injection pump timing.

High pressure fuel injection pump faulty.

Fuel Injectors faulty.

Fuel injector pipes incorrectly fitted.

High pressure system loss of pressure.

Failure of an electronic control system sensor / wiring.

Fault codes logged on Diesel control unit preventing startup. Failure of Diesel control unit .

Air intake System blocked / restricted.

Exhaust system blocked or restricted.

Engine condition causing low compression pressure.

Diesel injection pump not delivering fuel
Engine Starts then stops within a few seconds
Restricted fuel supply.
Air entering fuel system.
Immobiliser fault.
Faulty or incorrect ESOS (engine stop solenoid) or ELAP.
Electronic engine control fault.
Air intake restriction.
Exhaust system blocked / restricted.
Unstable Idling
Fuel supply restriction.
Air entering fuel system.
Electronic control system fault.
Blocked /leaking /inoperative fuel Injector.
Mechanical Injection pump fault (possible pump phasing).
Incorrect pump to engine timing.
Valve timing or compression problem.
Heater plug circuit fault.
Air intake system fault.
Exhaust partially blocked.
Exhaust gas recirculation (EGR) system fault.
Engine compression fault.
Excessive mechanical noise.
Insecure engine component / mechanical failure.
Incorrectly fitted timing belt.
Incorrect pump / valve / engine timing.
Incorrect fuel injector calibration / fault.
Incorrect Injection pump calibration.
Precombustion chamber loose in cylinder head.
Exhaust system blockage.
Excess black exhaust smoke emission
Faulty / dirty fuel injectors.
Incorrect injection pump to engine timing.
Injection pump overfuelling / incorrect calibration.
Injection pump excess fuel device fault.
Electronic control system fault.
Restricted air intake or air filter blocked.
Engine not reaching operating temperature.
Heater plug post heat fault.
Turbocharger oil seals allowing engine oil into air intake system.
Low boost pressure from turbo or intake system leaks.

Excess White / Grey smoke emission
Low injector opening pressure.
Incorrect valve timing.
Incorrect injection pump timing.
Low cylinder compression pressure.
Restricted air intake.
Low turbocharger boost pressure due to worn turbo / intake system fault / boost control.
Water entering combustion chambers due to head gasket failure, cylinder head or block cracked.
Incorrect valve timing.
Incorrect valve clearance.
Compression loss.
Faulty fuel injector / calibration.
Faulty Injection pump.
Air entering fuel system.
Fuel line restriction.
Random engine acceleration
Engine gaining extra fuel from supplementary source, eg ,
mechanical pump boost control diaphragm leaking fuel into turbo through boost control pipework.
Excessive engine oil level : Engine inducting engine oil & using as a fuel.
Electronic control system fault.
Faulty fuel injection pump.
Accelerator linkage insecure.
Slow deceleration
Restricted fuel return line.
Insecure accelerator linkage or return spring missing.

Low or Insufficient power

Restricted fuel supply.

Contaminated fuel.

Injectors faulty.

Fuel Pump calibration fault.

Incorrect valve or fuel pump timing.

Fuel pump stop solenoid not opening fully.

Accelerator linkage insecure or travel restricted.

Electronic engine control system or wiring fault.

Electronic diesel control system in limp home mode or restricted mode.

Turbocharger system fault.

Restricted exhaust system.
Exhaust Gas Recirculation fault (may log ecu fault codes eg, P0400 )

Road speed limiter incorrectly set or system fault.

Engine temperature fault.

Vehicle braking system not releasing.


Low coolant level, or coolant leakage.
Blocked radiator.
Faulty viscous fan , or fan motor not operating , wiring fault.
Incorrect injection pump calibration.
Faulty fuel injectors.
Incorrect injection pump timing , or electronic control system fault.
Mechanical fault with engine, gasket failure, cracked head,cracked block, cooling pressure cap faulty.
Excessive engine load due to vehicle brakes sticking on etc.

Engine will not shut off

Engine gaining a supplementary fuel supply.
Ignition switch / wiring fault leaving fuel stop solenoid energised.
Faulty fuel stop solenoid.
Stop control linkage disconnected or broken.




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