The ignition module, often identified by part numbers like 166 0785, plays a crucial role in a vehicle’s ignition system. This component is responsible for triggering the spark that ignites the air-fuel mixture in the engine cylinders. When an ignition module fails, the engine won’t start. This article explores a simple method using a soldering gun to test an ignition module, particularly relevant for older GM vehicles (circa 1974-1990s) that utilized a distributor and pickup coil system.
A common cause of no-start issues is a lack of spark due to a faulty ignition module. Before condemning the module, however, it’s crucial to confirm it’s receiving the necessary 12 volts and has a proper ground. This test, using a soldering gun, helps determine if the module is capable of responding to a triggering pulse. The process involves applying an AC magnetic field near the module to simulate the signal it normally receives from the pickup coil in the distributor.
For this test, disconnect the high tension lead from the distributor cap. If it’s an HEI (High Energy Ignition) system, disconnect the spark plug wire from a specific cylinder at the spark plug itself, ensuring the rotor is aligned with that cylinder. Connect a spark tester to the disconnected wire and ground it. With the key in the “on” position, hold an energized soldering gun close to the ignition module inside the distributor.
A functioning module will detect the AC magnetic field generated by the soldering gun and trigger the coil, causing the spark tester to fire rapidly (approximately 60 times per second, corresponding to a 60Hz frequency). If the spark tester fires, the issue likely lies with the pickup coil or crank trigger. Conversely, if no spark is observed, the ignition module (potentially a 166 0785 or similar) is likely faulty.
While this method isn’t foolproof, it offers a quick preliminary diagnosis for no-spark conditions related to the ignition module. Remember to always ensure proper voltage and grounding before conducting this test. If you can apply 12 volts to the module with a solid ground and connect a spark tester to the coil wire, this soldering gun trick may help determine if the module, such as a 166 0785, is the source of the problem. This method, while effective for older GM systems, may not be applicable to all vehicle makes and models.
