GM 94840127 Ignition Coil

If the engine is hard to start, misses at high speed, or cuts out during acceleration, the coil may be faulty. Ensure the battery and distributor are in good condition, the points are properly adjusted, and the plugs and plug wires are in good shape. Before conducting electrical checks on the coil, confirm it is clean and connections are tight and free of corrosion. Detach the coil high tension cable from the distributor cap, hold the end of the cable near a grounded part of the engine, turn on the ignition, and operate the starter; a bright blue spark should jump the gap. If the spark is weak or absent, check the coil's primary and secondary resistance. If the coil checks out but the engine still has issues, reversed coil polarity may be the cause. To check for this, remove a spark plug lead and hold it near the spark plug terminal while inserting a pencil between the ignition lead and the plug. For HEI ignition, remove the distributor cap and use an ohmmeter to check the primary coil terminals and secondary terminal resistance. If resistance readings are not as specified, replace the coil. For replacement, detach the battery cable, disconnect the high tension cable, and remove electrical connections from the coil terminals, marking them for correct reinstallation. Installation follows the reverse order, ensuring the center electrode is in good condition.

To check pick up coil first you need to remove the distributor cap, then you have to remove the rotor and you have to disconnect the pick-up coil leads from the module. Short an ohmmeter between the pick-up connector or wire and ground by touching each terminal, one at a time, and take note of the reading; an ohmmeter reading for a good pick-up coil should be infinity; if it is anything less than the pick-up coil is bad. Fourth, switch the ohmmeter towards both terminals on the pick-up coil connector, vacuum to the vacuum advance unit if it exists, and therefore the ohmmeter should read steady a minimum of 500 accompanied with a maximum of 1500 ohms while bending the wires; a failure here also implies a faulty pick-up coil. If the pick-up coil does not pass either test it should be replaced. This is eliminated, and instead, remove the distributor and mark the shaft and gear for gear assembly again. Place the distributor shaft housing in a bench vise; push out the roll pin to removed the gear and tanged washer-, check if there are burr in the shaft before pulling up the shaft. Three of the screws need to be unscrewed to remove the magnetic shield, as well as it is necessary to insert a flat-head screw-driver under the c-clip and turn it and pull out to remove the pick-up coil assembly. Put in the new pick-up coil assembly and make sure that the C-clip is in place, replace the shaft, make sure is clean and greased. Next piece is the tanged washer, fit it in such a way that the tangs are facing up, then the gear and then the roll pin. Rotate the shaft so that the teeth of the distributor shaft do not make any contact with the pick-up coil pole piece; if they make contact then adjust the pole piece and tighten it. Finally, reinstall the distributor.