Ignition system - testing
Note: Refer to the precautions given in Section 1 before proceeding.
Contact breaker ignition system 1 By far the majority of breakdown and running troubles are caused by faults in the ignition system either in the low tension or high tension circuits.
2 There are two main symptoms indicating faults. Either the engine will not start or fire, or the engine is difficult to start and misfires. If it is a regular misfire (ie the engine is running on only two or three cylinders), the fault is almost sure to be in the secondary or high tension circuit. If the misfiring is intermittent the fault could be in either the high or low tension circuits. If the car stops suddenly, or will not start at all, it is likely that the fault is in the low tension circuit. Loss of power and overheating, apart from faulty carburation settings, are normally due to faults in the distributor or to incorrect ignition timing.
Engine fails to start
3 If the engine fails to start and the car was running normally when it was last used, first check there is fuel in the petrol tank. If the engine turns over normally on the starter motor and the battery is evidently well charged, then the fault may be in either the high or low tension circuits. First check the HT circuit.
4 One of the commonest reasons for bad starting is wet or damp spark plug leads and distributor. Remove the distributor cap. If condensation is visible internally dry the cap with a rag and also wipe over the leads. Refit the cap. A moisture dispersant can be very effective in these situations.
5 If the engine still fails to start, check the voltage is reaching the plugs by disconnecting each plug lead in turn at the spark plug end, and holding the end of the cable about 3⁄16 inch (5 mm) away from the cylinder block. Spin the engine on the starter motor.
6 Sparking between the end of the cable and the block should be fairly strong with a strong regular blue spark. (Hold the lead with rubber to avoid electric shocks). If voltage is reaching the plugs, then remove them and clean and regap them. The engine should now start.
7 If there is no spark at the plug leads, take off the HT lead from the centre of the distributor cap and hold it to the block as before. Spin the engine on the starter once more. A rapid succession of blue sparks between the end of the lead and the block indicate that the coil is in order and that the distributor cap is cracked, the rotor arm is faulty, or the carbon brush in the top of the distributor cap is not making good contact with the rotor arm.
8 If there are no sparks from the end of the lead from the coil, check the connections at the coil end of the lead. If it is in order start checking the low tension circuit.
9 Use a 12v voltmeter or a 12v bulb and two lengths of wire. With the ignition switched on and the points open, test between the low tension wire to the coil and earth. No reading indicates a break in the supply from the ignition switch. Check the connections at the switch to see if any are loose. Refit them and the engine should run.
10 With the points still open take a reading between the moving point and earth. No reading here indicates a break in the wire or poor connections between the coil “-” terminal and distributor, or a faulty coil. Take a further reading between the coil “- “ terminal and earth. No reading confirms a faulty coil.
For these tests it is sufficient to separate the points with a piece of dry paper while testing with the points open.
11 If the engine misfires regularly, run it at a fast idling speed. Pull off each of the plug caps in turn and listen to the note of the engine. Hold the plug cap in a dry cloth or with a rubber glove as additional protection against a shock from HT supply.
12 No difference in engine running will be noticed when the lead from the defective circuit is removed. Removing the lead from one of the good cylinders will accentuate the misfire.
13 Hold the lead about 3/16 inch (5 mm) away from the block. Re-start the engine. If the sparking is fairly strong and regular, the fault must lie in the spark plug.
14 The plug may be loose, the insulation may be cracked, or the points may have burnt away giving too wide a gap for the spark to jump. Worse still, one of the points may have broken off. Either renew the plug, or clean it, reset the gap and then test it.
15 If there is no spark at the end of the plug lead, or if it is weak and intermittent, check the ignition lead from the distributor to the plug. If the insulation is cracked or perished, renew the lead. Check the connections at the distributor cap.
16 If there is still no spark, examine the distributor cap carefully for tracking. This can be recognised by a very thin black line running between two or more electrodes, or between an electrode and some other part of the distributor. These lines are paths which now conduct electricity across the cap thus letting it run to earth. The only answer is a new distributor cap.
17 Apart from the ignition timing being incorrect, other causes of misfiring have already been dealt with under the Section dealing with the failure of the engine to start.
To recap, these are that
a) The coil may be faulty giving an
b) There may be a damaged wire or loose connection in the low tension circuit; c) The condenser may be faulty; or d) There may be a mechanical fault in the distributor (broken driving spindle or contact breaker spring).
18 If the ignition timing is too far retarded, it should be noted that the engine will tend to overheat, and there will a quite noticeable drop in power. If the engine is overheating and the power is down, and the ignition timing is correct, then the carburettor should be checked, as it is likely that this is where the fault lies.
Electronic breakerless ignition 19 Testing of the electronic ignition system can only be accurately carried out using Ford dedicated test equipment and a systematic test procedure. For this reason any suspected faults in the system must be referred to a Ford dealer.
Programmed electronic ignition
(RS Turbo models)
20 Refer to paragraph 19.
Programmed electronic ignition (1.4 litre fuel injection models) 21 Complete and accurate fault diagnosis is only possible using special test equipment available to a Ford dealer.
22 Where a component is obviously defective, it can be removed and a new component fitted in its place.
23 Although certain electrical checks can be carried out to establish continuity or resistance, this is not recommended as the incorrect use of test probes between component connector pins can cause damage to the internal circuitry of some components.
24 Following the disconnection of the battery, all of the system Keep Alive Memory (KAM) values will be erased from the EEC IV module memory, which may result in erratic idle, engine surge, hesitation and a general deterioration of driving characteristics.
25 After reconnecting the battery, start the engine and allow it to idle for at least three minutes. After normal operating temperature is reached, increase the engine speed to 1200 rpm and maintain this speed for at least two minutes.
26 This procedure will allow the module to “re-learn” its reference values. It may be necessary to drive the vehicle for approximately five miles of varied driving to complete the learning process.
Distributorless ignition system
27 Refer to paragraphs 21 to 23.
1.6 litre Electronic Fuel Injection
28 Refer to paragraphs 24 to 26.
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