ENGINE FAILS TO START
If the engine won't start, perform a spark test as described earlier. If no spark occurs, check for the presence of normal battery voltage at the battery (BAT) terminal in the distributor cap. The ignition switch must be in the ON position for this test. Either a voltmeter or a test light may be used for this test. Connect the test light wire to ground and the probe end to the BAT terminal at the distributor. If the light comes on, you have voltage to the distributor. If the light fails to come on, this indicates an open circuit in the ignition primary wiring leading to the distributor. In this case, you will have to check wiring continuity back to the ignition switch using a test light. If there is battery voltage at the BAT terminal, but no spark at the plugs, then the problem lies within the distributor assembly. Go on to the distributor components test section.
Ignition Coil
See Figure 1
Detach wiring connector from cap.
Turn four latches using a screwdriver and remove cap and coil assembly from lower housing.
Connect an ohmmeter between distributor cap terminals "TACH" and "BAT" to test the ignition coil's primary coil. The primary coil resistance should be less than 1.0 ohm (zero or nearly zero).
Make the following ohmmeter measurements using a high resistance scale:
Connect an ohmmeter between the carbon button in the cap and the "GRD" terminal on the distributor cap to test the ignition coil's secondary coil. Record your reading.
Connect an ohmmeter between the carbon button in the cap and the "BAT" terminal on the distributor cap to test for short in the ignition coil. Record your reading.
If infinite ohms or resistance was measured in both measurements, the ignition coil is defective and needs to be replaced.
If the ignition coil tests OK, it's a good idea to test the pickup coil.
View Full Image Fig. 1: Checking coil resistance on the HEI system. Ohmmeter 1 shows the primary coil resistance connection. Ohmmeter 2 shows the secondary resistance connection. 1980 models shown, others similar
These resistance checks will not disclose shorted coil windings. This condition can be detected only with scope analysis or a suitably designed coil tester. If these instruments are unavailable, replace the coil with a known good coil as a final coil test.
Pick-Up Coil
See Figure 2
To test the pick-up coil, first disconnect the white and green module leads. Set the ohmmeter on the high scale and connect it between a ground and either the white or green lead. Any resistance measurement less than infinity requires replacement of the pick-up coil.
Pick-up coil continuity is tested by connecting the ohmmeter (on low range) between the white and green leads. Normal resistance is between 500 and 1500 ohms. Move the vacuum advance arm while performing this test. This will detect any break in coil continuity. Such a condition can cause intermittent misfiring. Replace the pick-up coil if the reading is outside the specified limits.
View Full Image Fig. 2: Checking the pick-up coil
If no defects have been found at this time, and you still have a problem, then the module will have to be checked. If you do not have access to a module tester, the only possible alternative is a substitution test. If the module fails the substitution test, replace it.
Ignition Module
The ignition module can only be tested using an ignition module tester. Since these testers are not readily available to the average do-it yourselfer, if you suspect that the ignition module is bad, its a good idea to check all the other components of the HEI system before replacing the module. Pay particular attention to all the wiring connections, since many times these connections vibrate loose or corrode. What looks like a good connection may not be, so be sure to clean all connections and disconnect and reconnect all connections.
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+15 years experience with Chevrolet. Bumper to bumper diagnosis & repair.