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ENGINE FAULT-TRACING
Serious mechanical trouble is comparatively rare, but minor troubles do unexpectedly crop up, although regular maintenance will go a long way towards preventing them. The accompanying fault-tracing chart illus- trates the systematic procedure which should be followed in diagnosis. Haphazard tests and tinkering are seldom very effective. A good axiom to remember is that an engine which is in sound mechanical order cannot fail to start or run efficiently provided that ?
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The fuel system is supplying a correct mixture in adequate quantity,
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The mixture is properly compressed in the cylinders,
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The ignition system is providing good sparks at the correct intervals,
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The cooling system is maintaining the engine at the right working temperature, and
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Adequate lubrication is preventing friction and heat.
By eliminating one or more of the above by tests, the field of inquiry can be gradually narrowed down by reference to the more detailed information in this and other chapters.
Fault Finding Chart
Starter Motor
Fails to crank engine: Battery discharged
Lead disconnected or corroded
Faulty starter switch
Drive dirty
Drive spring broken
Faulty starter motor Cranks engine slowly Battery partly discharged
Terminal loose
Connexions dirty
Wrong grade of oil
Faulty starter motor
Engine Will Not Fire
IGNITION
FUEL SYSTEM
Check Sparking Plugs
No spark at plug gap: Sparking plugs oiled up
Sparking plug porcelain cracked No petrol in carburettor Air leak in petrol line
Blockage in carburettor pipe line
Faulty petrol pump
Petrol tank empty
Check Distributor
No spark at plug leads: Cracked rotor
Loose low-tension leads
Faulty cap
Dirty or worn distributor points
Faulty condenser or connexions
Carbon brush not making contact Petrol in carburettor Mixture control faulty
Carburettor piston sticking
Air leak in induction manifold
Water in petrol
Dirt in carburettor
Check Coil
No spark at coil lead: Coil burnt out
High-tension lead loose or broken
Faulty switch
Points not opening or closing
Sparking Plug Test
Unscrew the plug, reconnect the lead and lay the plug on the cylinder block. Watch for a spark whilst the engine is turned over by hand
Check Battery
No lamps light or are weak Battery run down
Low-tension lead loose or broken
Symptom
Probable Cause
IGNITION FUEL SYSTEM MECHANICAL
Engine misfires High tension leads to sparking plugs shorting.
Incorrect spacing of sparking plug points.
Cracked sparking plug porcelain.
Battery connections loose.
Faulty or damp distributor cap. Water in carburettor.
Petrol line partly choked.
Fuel pump pressure low.
Fuel pump filter chocked.
Needle valve faulty or dirty.
Carburettor piston sticking.
Carburettor piston damper requires oil. Valves sticking.
Valves burnt or broken.
Valve spring broken.
Incorrect valce clearance.
Engine starts and stops Low-tension connection loose.
Faulty switch contact.
Dirty contact points. Petrol line blocked.
Water in petrol.
Needle valve sticking.
Fuel pump faulty.
Carburettor pistons sticking.
Air leaks.
Engine runs on wide throttle only Carburettor piston sticking.
Slow-running adjusting screw incorrectly adjusted. Valve sticking.
Valve burnt or broken.
Valve spring broken.
Engine does not give full power Ignition retarded.
High-tension lead shorting.
Faulty distributor cap. Petrol supply faulty.
Air leaks in induction pipe.
Jet partly blocked.
Carburettor piston sticking. Valve burnt or badly seated.
Incorrect valve clearance.
Engine runs imperfectly Timing incorrect. Carburettor flooding.
Weak mixture.
Petrol feed faulty. Inlet valve not closing.
Engine knocks Timing too far advanced. Excessive carbon deposits.
Loose bearings or pistons.
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