* Intermittent No-Start: This is the hallmark symptom. The engine cranks normally, but it won't fire. Then, after some time (could be minutes, hours, or even days), it starts perfectly again. This inconsistency is key. A completely dead module would leave you stranded.
* Misfires/Rough Running (before complete failure): Before completely failing, a weakening module might cause misfires, hesitation, or rough running, especially under load or at higher RPMs. This is a warning sign that the module is nearing its end.
* No Spark at the Plugs (when it won't start): The most definitive test is to check for spark at the spark plug wires when the engine fails to start. If there's no spark, the ignition module is a prime suspect. You'll need an inline spark tester or a spark checker to do this safely.
* Slow Cranking (less common but possible): While the most common issue is lack of spark, a severely failing module *might* draw excessive current, potentially leading to slower cranking. However, this is less frequent than spark issues.
Important Considerations:
* Other Possibilities: Before jumping to conclusions, rule out other potential causes of a no-start condition: bad crankshaft position sensor (CKP), distributor cap and rotor, coil, fuel pump issues, ignition switch problems, and faulty wiring.
* Testing the Module: Visually inspect the module for any obvious signs of damage (burnt components, loose connections). However, true diagnosis usually involves checking for spark, testing module resistance (with a multimeter, using the manufacturer's specifications), and possibly even using an oscilloscope to examine the signals going to and from the module.
If you are not comfortable with automotive electrical testing, it's best to take your truck to a qualified mechanic. Diagnosing ignition problems can be tricky, and incorrectly replacing parts can be costly and time-consuming. Starting with a comprehensive spark test is the most efficient first step.
