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Ignition system - testing
Engine electrical systems / Ignition system - testing


Warning: Because of the high voltage generated by the ignition system, extreme care should be taken whenever an operation is performed involving ignition components. This not only includes the ignition module/ECU, coil and spark plug (HT) leads, but related components such as electrical connectors, tachometer and other test equipment also.

Note: This is an initial check of the ignition part of the main engine management system, to be carried out as part of the preliminary checks of the complete engine management system (see Chapter 6).

1 If the engine turns over but wont start, disconnect the (HT) lead from any spark plug, and attach it to a calibrated tester (available at most automotive accessory shops). Connect the clip on the tester to a good earth - a bolt or metal bracket on the engine. If youre unable to obtain a calibrated ignition tester, have the check carried out by a Ford dealer service department or similar. Any other form of testing (such as jumping a spark from the end of an HT lead to earth) is not recommended, because of the risk of personal injury, or of damage to the ECU/ignition module (see notes above and in Section 4).

2 Crank the engine and watch the end of the tester to see if bright blue, well-defined sparks occur.

3 If sparks occur, sufficient voltage is reaching the plug to fire it. Repeat the check at the remaining plugs, to ensure that all leads are sound and that the coil is serviceable.

However, the plugs themselves may be fouled or faulty, so remove and check them as described in Chapter 1.

4 If no sparks or intermittent sparks occur, the spark plug lead(s) may be defective - check them as described in Chapter 1.

5 If theres still no spark, check the coils electrical connector, to make sure its clean and tight. Check for full battery voltage to the coil at the connectors centre terminal. The coil is earthed through the ECU - do not attempt to check this. Check the coil itself (see Section 6). Make any necessary repairs, then repeat the check again.

6 The remainder of the system checks should be left to a dealer service department or other qualified repair facility, as there is a chance that the ECU may be damaged if tests are not performed properly.


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