Volvo Coupes/Sedans/Wagons 1970-1989 Repair Guide

Troubleshooting the Electronic Ignition System

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An electronic ignition troubleshooting chart is included in Engine Electrical , along with a brief explanation of the Volvo electronic ignition system.

Troubleshooting procedures for breaker point ignition systems are found in this section.

IGNITION COIL



See Figure 1

All spark-ignition systems (gasoline engines) use a coil as the first component in the ignition system. The coil is simply a step-up transformer, which takes the 12 to 14 volts of the engine's electrical system and increases it to very high voltage. This change is necessary so that the electrical charge can form a sufficiently hot spark when it jumps to ground through the spark plug electrode gap.



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Fig. Fig. 1: The coil is easy to locate by tracing the center wire from the distributor cap back to the coil


CAUTION
Electronic ignition systems operate at very high voltages, often in excess of 30,000 volts. Such high voltages are a danger to life and special precautions must be taken on vehicles equipped with electronic ignition. Even the older, breaker point ignition systems can deliver a nasty shock to a careless worker.

The coil is easily found by tracing the center wire in the distributor cap to its opposite end. The coil is generally retained by a bracket, held to the car by one or two bolts. Depending on its position and ease of access, the coil may not need to be removed for testing.

To properly test a coil, you must have an ohmmeter. Generally, this tool is found as a volt/ohmmeter (VOM) and is very useful in automotive diagnosis. The resistance values for the primary side of the coil and ballast resistor (if so equipped) will be very low; make sure your VOM is set on the 0-10 ohm scale. When testing the secondary side of the coil, resistance will be much higher and the scale is usually set on 0-10,000 ohms.

Testing the Coil and Ballast Resistor

See Figures 2, 3, 4, 5 and 6

Perform this work with the engine OFF and the key out of the ignition so that there is NO possibility of the ignition being on. Carefully remove the wire to the distributor from the top of the coil. Label and disconnect the other wires attached to the coil, taking care not to lose any of the very small nuts and washers.



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Fig. Fig. 2: Inspect the top of the coil for any fine cracks-replace the coil if any are found



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Fig. Fig. 3: Label and disconnect the wires to ensure a correct installation

Clean off the coil and look for the numbers stamped near the terminals. Terminal No. 1 is ground (or negative), No. 15 is PRIMARY voltage (12 volts) and the terminal labeled HT is SECONDARY or high tension voltage. The HT terminal is the center tower, from which runs the wire to the distributor. Inspect the tower for any signs of cracking. If cracks are found, replace the coil. Check carefully, most coil cracks are hairline thin and hard to see.



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Fig. Fig. 4: Check the coil primary windings using terminals 1 and 15



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Fig. Fig. 5: Check the coil secondary windings using terminal 1 and the HT port



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Fig. Fig. 6: Use an ohmmeter to check the resistance of the coil ballast

To measure the primary side of the coil, connect the leads of the meter to terminals 1 and 15. To read the secondary side, connect to terminals 1 and HT.

The values given in the accompanying chart are based on a coil temperature of 68°F (20°C).

 
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