someone else, who may not have described it
very accurately.
Don’t overlook the obvious. For example, if
the vehicle won’t start, is there petrol in the
tank? (Don’t take anyone else’s word on this
particular point, and don’t trust the fuel gauge
either!) If an electrical fault is indicated, look
for loose or broken wires before digging out
the test gear.
Cure the disease, not the symptom.
Substituting a flat battery with a fully-charged
one will get you off the hard shoulder, but if
the underlying cause is not attended to, the
new battery will go the same way. Similarly,
changing oil-fouled spark plugs (petrol
models) for a new set will get you moving
again, but remember that the reason for the
fouling (if it wasn’t simply an incorrect grade
of plug) will have to be established and
corrected.
Don’t take anything for granted. Particularly,
don’t forget that a “new” component may
itself be defective (especially if it’s been
rattling around in the boot for months), and
don’t leave components out of a fault
diagnosis sequence just because they are
new or recently-fitted. When you do finally
diagnose a difficult fault, you’ll probably
realise that all the evidence was there from
the start.
Fault finding REF•11
REF
1 Engine
Engine fails to rotate when attempting to start
mm Battery terminal connections loose or corroded (“Weekly checks”).
mm Battery discharged or faulty (Chapter 5A).
mm Broken, loose or disconnected wiring in the starting circuit
(Chapter 5A).
mm Defective starter solenoid or switch (Chapter 5A).
mm Defective starter motor (Chapter 5A).
mm Starter pinion or flywheel ring gear teeth loose or broken (Chapters
2A, 2B, 2C and 5A).
mm Engine earth strap broken or disconnected (Chapter 5A).
mm Automatic transmission selector not in N, or inhibitor switch faulty
(Chapter 7B).
Engine rotates, but will not start
mm Fuel tank empty.
mm Battery discharged (engine rotates slowly) (Chapter 5A).
mm Battery terminal connections loose or corroded (“Weekly checks”).
mm Ignition components damp or damaged (Chapters 1 and 5B).
mm Worn or incorrectly adjusted contact breaker points (Chapter 5B).
mm Broken, loose or disconnected wiring in the ignition circuit
(Chapters 1 and 5B).
mm Worn, faulty or incorrectly-gapped spark plugs (Chapter 1).
mm Choke mechanism incorrectly adjusted, worn or sticking -
carburettor models (Chapter 4A).
mm Fuel injection system fault - fuel injected models (Chapter 4B or 4C).
mm Major mechanical failure (eg camshaft drive) (Chapter 2A or 2B).
Engine difficult to start when cold
mm Battery discharged (Chapter 5A).
mm Battery terminal connections loose or corroded (Chapter 1).
mm Worn, faulty or incorrectly-gapped spark plugs (Chapter 1).
mm Worn or incorrectly adjusted contact breaker points (Chapter 5B).
mm Choke mechanism incorrectly adjusted, worn or sticking -
carburettor models (Chapter 4A).
mm Fuel injection system fault - fuel injected models (Chapter 4B or 4C).
mm Other ignition system fault (Chapters 1 and 5B).
mm Low cylinder compressions (Chapter 2A or 2B).
Engine difficult to start when hot
mm Air filter element dirty or clogged (Chapter 1).
mm Choke mechanism incorrectly adjusted, worn or sticking -
carburettor models (Chapter 4A).
mm Fuel injection system fault - fuel injected models (Chapter 4B).
mm Worn or incorrectly adjusted contact breaker points (Chapter 5B).
mm Uneven or low cylinder compressions (Chapter 2A).
Starter motor noisy or excessively-rough in
engagement
mm Starter pinion or flywheel ring gear teeth loose or broken
(Chapters 2A, 2B and 5A).
mm Starter motor mounting bolts loose or missing (Chapter 5A).
mm Starter motor internal components worn or damaged (Chapter 5A).
Engine starts, but stops immediately
mm Loose or faulty electrical connections in the ignition circuit
(Chapters 1 and 5B).
mm Vacuum leak at the carburettor/throttle body or inlet manifold
(Chapter 4A, 4B or 4C).
mm Worn or incorrectly adjusted contact breaker points (Chapter 5B).
mm Ballasted ignition system fault (Chapter 5B).
mm Blocked injector/fuel injection system fault - fuel injected models
(Chapter 4B).
Engine idles erratically
mm Air filter element clogged (Chapter 1).
mm Vacuum leak at the carburettor/throttle body, inlet manifold or
associated hoses (Chapter 4A, 4B or 4C).
mm Worn, faulty or incorrectly-gapped spark plugs (Chapter 1).
mm Worn or incorrectly adjusted contact breaker points (Chapter 5B).
mm Uneven or low cylinder compressions (Chapter 2A).
mm Camshaft lobes worn (Chapter 2B).
mm Incorrect idle speed and mixture adjustment - carburettor models
(Chapter 4A).
mm Blocked injector/fuel injection system fault - fuel injected models
(Chapter 4B).
mm Incorrect valve clearances (Chapter 2A).
mm Broken valve spring(s) (Chapter 2B).
mm Burnt, sticking or leaking valves (Chapter 2B).
mm Worn valve stems or guides (Chapter 2B).
mm Worn or damaged pistons, piston rings and bores (Chapter 2B).
Engine misfires at idle speed
mm Worn, faulty or incorrectly-gapped spark plugs (Chapter 1).
mm Faulty spark plug HT leads (Chapter 1).
mm Worn or incorrectly adjusted contact breaker points (Chapter 5B).
mm Incorrect idle speed and mixture adjustment - carburettor models
(Chapter 4A).
mm Vacuum leak at the carburettor/throttle body, inlet manifold or
associated hoses (Chapter 4A, 4B or 4C).
mm Blocked injector/fuel injection system fault - fuel-injected models
(Chapter 4B).
mm Distributor cap cracked or tracking internally (Chapter 1).
mm Incorrect valve clearances (Chapter 2A).
mm Uneven or low cylinder compressions (Chapter 2A).
mm Disconnected, leaking, or perished crankcase ventilation hoses
(Chapter 4C).
Engine misfires throughout the driving speed
range
mm Fuel filter choked - fuel injected models (Chapter 1).
mm Incorrect idle speed and mixture adjustment - carburettor models
(Chapter 4A).
mm Incorrect ignition timing (Chapter 5B).
mm Choke mechanism incorrectly adjusted, worn or sticking -
carburettor models (Chapter 4A).
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