Opel Corsa B 1993–2000 Service and Repair Manual: Ignition system - testing

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 that 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. If the engine fails to start due to either damp HT leads or distributor cap, a moisture dispersant can be very effective. To prevent the problem recurring, a proprietry damp start product can be used to provide a sealing coat, so excluding any further moisture from the ignition system. In extreme difficulty, a proprietry cold start product will help to start a car when only a very poor spark occurs.

5. If the engine still fails to start, check that voltage is reaching the plugs by disconnecting each plug lead in turn at the spark plug end, and holding the end of the cable with rubber or an insulated tool about 6 mm away from the cylinder block. Spin the engine on the starter motor.

Note Do not operate the starter system with the plug leads disconnected in any other way to that described, or damage to system components may result.

6. Sparking between the end of the cable and the block should be fairly strong with a regular blue spark. 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 indicates 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 spring on 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. Possibly, the points are in bad condition. Clean and reset them.

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. A reading shows a faulty coil or condenser, or broken lead between the coil and the distributor.

10. Take the condenser wire off the points assembly and with the points open test between the moving point and earth. If there is now a reading then the fault is in the condenser. Fit a new one and the fault is cleared.

11. With no reading from the moving point to earth, take a reading between earth and the distributor terminal of the coil A reading here shows a broken wire which will need to be replaced between the coil and the distributor.

No reading confirms that the coil has failed and must be renewed, after which the engine will run once more. Remember to refit the condenser wire to the points assembly. For these tests it is sufficient to separate the points with a piece of dry paper while testing with the points open.

Engine misfires

12. 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 the HT supply.

13. 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.

14. Remove the plug lead from the plug which is not firing and hold it about 6 mm away from the block. Restart the engine. If the sparking is fairly strong and regular, the fault must lie in the spark plug.

15. 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.

16. 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.

17. 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.

18. Apart from the ignition timing being incorrect, other causes of misfiring have already been dealt with under the Selection dealing with the failure of the engine to start.

To recap, these are that:

1. The coil may be faulty giving an intermittent misfire.
2. There may be a damaged wire or loose connection in the low tension circuit.
3. The condenser may be faulty.
4. There may be a mechanical fault in the distributor (broken driving spindle or contact breaker spring).

19. If the ignition timing is too far retarded, it should be noted that the engine will tend to overheat, and there will be 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.