Engine - common problems

[Plex]

ENGINE FAULT FINDING

Engine fails to rotate when
attempting to start
� Battery terminal connections loose
or corroded (�Weekly checks�).
� Battery discharged or faulty.
� Broken, loose or disconnected wiring in
the starting circuit.
� Defective starter solenoid or switch.
� Defective starter motor.
� Starter pinion or flywheel/driveplate ring
gear teeth loose or broken.
� Engine earth strap broken or disconnected.

Engine rotates, but will not start
� Fuel tank empty.
� Battery discharged (engine rotates slowly).
� Battery terminal connections loose
or corroded (�Weekly checks�).
� Ignition components damp or damaged.
� Broken, loose or disconnected wiring in
the ignition circuit.
� Worn, faulty or incorrectly-gapped
spark plugs.
� Faulty choke or carburettor.
� Fuel injection system fault.
� Major mechanical failure
(e.g. broken timing chain).

Engine difficult to start when cold
� Battery discharged.
� Battery terminal connections loose
or corroded (�Weekly checks�).
� Worn, faulty or incorrectly-gapped
spark plugs.
� Faulty choke or carburettor.
� Fuel injection system fault.
� Other ignition system fault.
� Low cylinder compressions.

Engine difficult to start when hot
� Air filter element dirty or clogged.
� Faulty choke or carburettor.
� Fuel injection system fault.
� Low cylinder compressions.

Starter motor noisy or excessively-rough
in engagement
� Starter pinion or flywheel/driveplate ring
gear teeth loose or broken.
� Starter motor mounting bolts loose
or missing.
� Starter motor internal components worn
or damaged

Engine hesitates on acceleration
� Worn, faulty or incorrectly-gapped
spark plugs.
� Vacuum leak at the carburettor,
throttle body, inlet manifold
or associated hoses.
� Faulty carburettor.
� Fuel injection system fault.

Engine stalls
� Vacuum leak at the carburettor,
throttle body, inlet manifold
or associated hoses.
� Fuel filter choked.
� Fuel pump faulty, or delivery pressure low.
� Fuel tank vent blocked,
or fuel pipes restricted.
� Faulty carburettor.
� Fuel injection system fault.

Engine lacks power
� Timing belt incorrectly fitted or tensioned.
� Fuel filter choked.
� Fuel pump faulty, or delivery pressure low.
� Uneven or low cylinder compressions.
� Worn, faulty or incorrectly-gapped
spark plugs.
� Vacuum leak at the carburettor,
throttle body, inlet manifold
or associated hoses.
� Faulty carburettor.
� Fuel injection system fault.
� Brakes binding.
� Clutch slipping.

Engine backfires
� Timing belt incorrectly fitted or tensioned.
� Vacuum leak at the carburettor,
throttle body, inlet manifold
or associated hoses.
� Faulty carburettor.
� Fuel injection system fault. Engine starts, but stops immediately
� Loose or faulty electrical connections
in the ignition circuit.
� Vacuum leak at the carburettor, throttle body,
or inlet manifold.
� Faulty carburettor.
� Fuel injection system fault.

Engine idles erratically
� Incorrectly-adjusted idle speed.
� Air filter element clogged.
� Vacuum leak at the carburettor, throttle body,
inlet manifold or associated hoses.
� Worn, faulty or incorrectly-gapped
spark plugs.
� Uneven or low cylinder compressions.
� Camshaft lobes worn.
� Timing belt incorrectly tensioned.
� Faulty carburettor.
� Fuel injection system fault.

Engine misfires at idle speed
� Worn, faulty or incorrectly-gapped
spark plugs.
� Faulty spark plug HT leads.
� Vacuum leak at the carburettor, throttle body,
inlet manifold or associated hoses.
� Faulty carburettor.
� Fuel injection system fault.
� Distributor cap cracked or tracking internally.
� Uneven or low cylinder compressions.
� Disconnected, leaking,
or perished crankcase ventilation hoses.

Engine misfires throughout
the driving speed range
� Fuel filter choked.
� Fuel pump faulty, or delivery pressure low.
� Fuel tank vent blocked,
or fuel pipes restricted.
� Vacuum leak at the carburettor, throttle body,
inlet manifold or associated hoses.
� Worn, faulty or incorrectly-gapped
spark plugs.
� Faulty spark plug HT leads.
� Distributor cap cracked or tracking internally.
� Faulty ignition coil.
� Uneven or low cylinder compressions.
� Faulty carburettor.
� Fuel injection system fault.

Oil pressure warning light illuminated with
engine running
� Low oil level, or incorrect oil grade.
� Faulty oil pressure sensor.
� Worn engine bearings and/or oil pump.
� Excessively high engine operating temperature.
� Oil pressure relief valve defective.
� Oil pick-up strainer clogged.

Note: Low oil pressure in a high-mileage engine at tickover is not necessarily a cause for concern. Sudden pressure loss at speed is far more significant. In any event, check the gauge or warning light sender before condemning the engine.

Engine runs-on after switching off
� Excessive carbon build-up in engine.
� Excessively high engine operating temperature.

Engine noises Pre-ignition (pinking)
or knocking during acceleration
or under load
� Ignition timing incorrect/ignition system fault.
� Incorrect grade of spark plug.
� Incorrect grade of fuel.
� Vacuum leak at carburettor, throttle body,
inlet manifold or associated hoses.
� Excessive carbon build-up in engine.
� Faulty carburettor.
� Fuel injection system fault.

Whistling or wheezing noises
� Leaking inlet manifold or throttle body gasket.
� Leaking exhaust manifold gasket
� Leaking vacuum hose.
� Blowing cylinder head gasket.

Tapping or rattling noises
� Worn valve gear or camshaft.
� Incorrect valve clearances.
� Ancillary component fault
(water pump, alternator, etc).

Knocking or thumping noises
� Worn big-end bearings (regular heavy
knocking, perhaps less under load).
� Worn main bearings (rumbling and knocking,
perhaps worsening under load).
� Piston slap (most noticeable when cold).
� Ancillary component fault
(water pump, alternator, etc).