Mazda Trucks 1972-1986 Repair Guide

Ignition Coil

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TESTING



Piston Engines Through 1981

Measure the primary resistance by connecting an ohmmeter across the positive (+) and negative (-) terminals of the coil. Primary resistance, at 68ºF (20ºC), should be 0.9 omega +- 0.09 omega .

Measure the secondary resistance by connecting an ohmmeter across the center tower connector and the positive (+) terminal. Resistance, at 68ºF (20ºC), should be 6-30K omega .

If a megaohm tester is available, connect it between the negative (-) terminal and the outside of the coil casing. This will test the coil insulation and show if there is an internal short. Resistance, at 68ºF (20ºC), should be >10M omega .

1982-86 Piston Engines

  1. Connect an ohmmeter set to the X1 scale to the plug and minus primary connectors of the coil, as shown. The coil should have good continuity. That is, resistance should be approximately 1-1.3 omega except on the 2,654cc, on which the resistance should be approximately 0.72-0.88 omega .
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  3. Disconnect the high tension wire and move the connector leading to the minus terminal over to the metallic connector inside the coil tower. Set the ohmmeter to the X1000 scale. Resistance must be 10,000-30,000 omega .
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  5. You can also check for bad coil insulation by measuring the resistance between the coil (-) primary connection and the metal body (case) of the coil. If resistance is less than 10m omega , replace the coil. This test may not be entirely satisfactory unless you have a megaohm tester that records 500 volts. If the tests below do not reveal the problem and, especially, if operating the engine at night may produce some bluish sparks around the coil, you may want to remove the coil and have it tested at a diagnostic center.
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  7. If the coil resistances are not as specified, replace the coil.
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If the coil tests out ok, replace the igniter and pickup coil. However, you should make sure before doing this work that there are no basic maintenance problems in the secondary circuit of the system, since it is often impossible to return electrical parts. We suggest that before you replace the igniter and pickup coil, you carefully inspect the cap and rotor for carbon tracks or cracks and disconnect the wires and measure their resistance with an ohmmeter. Resistance should be 16,000 omega per length of 100cm. Also, check for cracks in the insulation. Replace secondary parts as inspection/testing deems necessary before replacing the igniter and pickup coil.

Rotary Engine

Two coils, leading and trailing, are used. The leading coil is type HP5-13J; the trailing, type HP5-13E.

  1. Measure the primary resistance by connecting an ohmmeter across the positive (+) and negative (-) terminals of the coil. Primary resistance, at 68ºF (20ºC), should be 1.35 omega on the leading coil; 1.46 omega on the trailing coil.
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  3. Measure the secondary resistance by connecting an ohmmeter across the center tower connector and the positive (+) terminal. Resistance, at 68ºF (20ºC), should be 8.7K omega on the leading coil; 9.5K omega on the trailing coil.
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  5. Check across the external resistor on each coil. Resistance, at 68ºF (20ºC), should be 1.4 omega on the leading coil; 1.6 omega on the trailing coil.
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REMOVAL & INSTALLATION



  1. Disconnect the negative battery cable and make sure the ignition switch is off. Remove any protective boots from the top of the coil, if necessary by sliding them back the coil-to-distributor wire.
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  3. Carefully pull the high tension wire out of the coil, twisting it gently as near as possible to the tower to get it started.
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  5. Note the routing and colors of the primary wires, and then remove nuts and lockwashers, retaining all parts for installation. Clean the primary terminals with sandpaper, if necessary, to ensure a clean connection. Then, loosen the through bolt or bolts which clamp the coil in place and slide the coil out of its mount.
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  7. Install the new coil in exact reverse order, making sure the primary connections are tight. Ensure also that the coil-to-distributor wire is fully seated in the tower and that the protective boot is fully installed on the outside of the tower.
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