FAULT FINDING
This is a logical and progressive method of Fault Finding that aims to help you to overcome the main faults that can affect the mobility or safety of your "Spridget" or similar era vehicle. It also helps you to overcome the problem that has affected most mechanics - amateur and professional at one time or another... Blind Spot Syndrome!


It goes like this: the vehicle refuses to start one damp Sunday morning. You decide that there must be no fuel getting through. By the time you’ve stripped the fuel pump, carburettor fuel lines and "unblocked" the fuel tank, it’s time for bed. And the next day, the local garage finds that your main HT lead has dropped out of the coil! Something like that has happened to most of us!
Don’t jump to conclusions: if your engine won’t start or runs badly, if electrical components fail, follow the logical numbered sequence of checks listed here in the Charts, and detailed overleaf, eliminating each "check" (by testing - not by "hunch") before moving on to the next. Remember that the great majority of failures are caused by electrical or ignition faults: only a minor proportion of engine failures come from the fuel system. Follow the sequences shown here - and you’ll have better success in finding that fault. Before carrying out any of the work described in this section please read carefully information on Safety First when working on or under vehicles! The numbers on those Charts refer to the following points:-

Engine Won’t Start Chart
1. Starter motor doesn’t turn.
2. Starter motor turns slowly.
3. Starter motor noisy or harsh.
4. Starter motor turns engine but vehicle will not start.
See ‘Ignition System’ box.
5. Is battery okay?
6. Can engine be rotated by hand?
7. Check battery connections for cleanliness/tightness.
8. Test battery with voltmeter.
9. Have battery ‘drop’ test carried out by specialist.

Ignition System Chart


17. Check for spark at plug (remove plug and prop it with threads resting on bare metal of cylinder block). Do not touch plug or lead while operating starter.
18. If no spark is present at plug, check for spark at contact breaker points when ‘flicked’ open (ignition ‘on’). Double-check to ensure that points are clean and
correctly gapped, and try again.
19. If spark present at contact breaker points, check for spark at central High
Tension lead from coil.(Hold HT Lead with insulated pliers (or similar) about 2cms. from its coil connection, and with ignition on, turn motor over a few times). Sparks should ‘crack’ and jump between lead and coil.
20. If spark present at central high tension lead from coil, check distributor cap
and rotor arm; replace if cracked (look for ‘carbon line traces’) or contacts badly worn.
21. If distributor cap and rotor arm are okay, check high tension leads and connections - replace leads if they are old carbon core type suppressed variety.
22. If high tension leads are sound but dirty or damp, clean/dry them.
23. If high tension leads okay, check/clean/dry/re-gap sparking plugs.
24. Damp conditions! Apply water repellent spray to ignition system.
25. If no spark present at contact breaker points, examine connections of low tension leads between ignition switch and coil and from coil to contact breaker (including short low-tension lead within distributor).
26. If low tension circuit connections okay, examine wiring.
27. If low tension wiring is sound, is condenser okay! If in doubt, fit new condenser.
28. If condenser is okay, check for spark at central high tension lead from coil.
29. If no spark present at central high tension lead from coil, check for poor high tension lead connections.
30. If high tension lead connections okay, is coil okay? If in doubt, fit new coil.
31. 1f spark present at plug, is it powerful or weak? If weak, see ‘27’.
32. If spark is healthy, check ignition timing.
33. If ignition timing is okay, see ‘Fuel System’ box (see 36).

Fuel System Chart

 
34. Check briefly for fuel at feed pipe to carburettors. (Disconnect pipe and turn ignition ‘on’ ensuring pipe is aimed away from hot engine and exhaust components and into a suitable container). If no fuel present at feed pipe, is petrol tank empty?! (Rock vehicle and listen for ‘sloshing’ in tank as well as looking at gauge). If you have twin-tanks or fuel cut-off switch in vehicle, make sure that the switch is correctly positioned.
35. If tank is empty, replenish!


36. If there is petrol in the tank but none issues from the feed pipe from pump to carburettor, check that the small vent hole in the fuel filler cap is not blocked and so causing a vacuum.


37. Check for a defective fuel pump. With outlet pipe disconnected AND


AIMED AWAY FROM PUMP AND HOT EXHAUST COMPONENTS, ETC. as well as your eyes and clothes, aim into a suitable container, turn the engine over and fuel should issue from pump outlet at the correct rate as per Manual.


38. If pump is okay, check for blocked fuel filter or pipe, or major leak in pipe between tank and pump, or between pump and carbies.


39. If the filter is clean and the pump operates, suspect blocked carburettor


jet(s) or damaged/sticking float or incorrectly adjusted carburettor.


40. If fuel is present at carburettor feed pipe, remove spark plugs and check to see if wet with unburnt fuel.
41. If the spark plugs are fuel-soaked, check that the manual or automatic choke (if fitted) is operating as it should and is not jammed ‘shut’. Other possibilities include float needle valve(s) sticking ‘open’ or leaking, float punctured, carburettor incorrectly adjusted or air filter totally blocked. Clean plugs before replacing.
42. If the spark plugs are dry, check whether the float needle valve is jammed ‘shut’.
43. Check for severe air leak at inlet manifold gasket or carburettor gasket, or incorrectly set valve clearances.
FUEL SYSTEM- SAFETY FIRST!
Before working on the fuel system read about ‘Safety First’. Take special care to 1) only work out of doors 2) wear suitable gloves and goggles and keep fuel out of eyes and away from skin: it is known to be carcinogenic. 3) if fuel does come into contact with skin wash off straight away. 4) if fuel gets into your eyes, wash out with copious amounts of clean cold water. Seek medical advice if necessary. 5) when draining fuel or testing for fuel flow, drain or pump into a sufficiently large container, minimising splashes. 6) don’t smoke, work near flames or sparks or work when the engine or exhaust are hot.

Engine Lacks Power Chart


44. Engine overheating. Check oil temperature gauge (where fitted). Low oil pressure light (if fitted) may come on.
45. Thermostat not opening/closing at the correct temperatures or the cooling
air flaps (if fitted) not operating because they’ve seized. If you car’s carburation has an air inlet connected to a heater chamber on the exhaust manifold check that: i) the pipe is in place and not split and, ii) any thermostatic valve or flap is operating correctly. If not, the car can stop and restart intermittently because of inlet icing in freezing weather.
46. If thermostat/air flaps okay, check oil level. BEWARE - DIPSTICK AND OIL MAY BE VERY HOT. Also, check for loss of coolant. WAIT UNTIL THE ENGINE HAS FULLY COOLED BEFORE ATTEMPTING TO REMOVE RADIATOR CAP. USE A RAG TO PROTECT HANDS WHEN RELEASING CAP, AND KEEP FACE WELL CLEAR IN CASE COOLANT SPRAYS OUT. If coolant level is low, check hoses and connections, water pump and cylinder block for leaks. Rectify and top up system.
47. If oil level okay, check for slipping fan belt, cylinder head gasket ‘blown’, partial mechanical seizure of engine (pistons? bearings?), blocked or damaged exhaust system. If the Head Gasket is ‘blown’ into the ‘water jacket’, bubbles will appear in the radiator whilst engine is running, or if blown to the outside of the head, a harsh exhaust popping sound will be heard, or if blown between cylinders, a popping back out of a carburettor throat could occur and a compression test of the suspect cylinders will register a low reading. Strange noises should be investigated.
48. If engine temperature is normal, check cylinder compressions.
49. If cylinder compression readings low, add a couple of teaspoons of engine oil to each cylinder in turn, and repeat test. If readings don’t improve, suspect burnt
valves/seats.
50. If compression readings improve after adding oil as described, suspect worn cylinder bores, pistons and rings.
51. If compression readings are normal, check for mechanical problems. For example, binding brakes, slipping clutch, partially seized transmission etc.

Engine Stops Suddenly Chart
52. Check for sudden ingress of water/snow onto ignition components, (particularly the Distributor and leads) in adverse weather conditions. Sudden failure is almost always because of an ignition fault. Check for simple wiring and connection breakdowns.

Lights Fail Chart
53. Sudden failure - check fuses.
54. If all lamps affected, check switch and main wiring feeds.


55. If not all lamps are affected, check bulbs on lamps concerned.


56. If bulbs appear to be okay, check bulb holder(s), local wiring and connections.


57. If bulb(s) blown, replace!


58. Intermittent operation, flickering or poor light output - check earth (ground) connections(s).


59. If earth(s) okay, check switch.


60. If switch okay, check wiring and connections.

Horn Failure Chart
61. If horn does not operate, check fuse, all connections (particularly earths/grounds) and cables. Remove horn connections, check and clean. Use 12v test lamp to ascertain if power getting to horn.
62. If horn will not stop(!), disconnect the horn and check for earthing of cable between button and horn unit, and the wiring in the horn switch housing.

Fuel Gauge Problems Chart


63. Gauge reads ‘empty’ - check for fuel in tank.
64. If fuel is present in tank, check for earthing and wiring from tank to gauge and for wiring disconnections.
65. Gauge permanently reads ‘full’, regardless of tank contents. Check wiring and connections as in ‘66’.
66. If wiring and connections all okay, sender unit/fuel gauge defective.
67. With wiring disconnected, check for continuity between fuel gauge terminals. Do NOT test gauge by short-circuiting to earth. Replace unit if faulty.
68. If gauge is okay, disconnect wiring from tank sender unit and check for continuity between terminal and case. Replace sender unit if faulty.