1. Ignition System Components:
* Ignition Coil: This is a common failure point. Check the coil for cracks, corrosion, or damage. You can usually test the coil's primary and secondary resistance with a multimeter (consult a wiring diagram for your specific vehicle to find the correct test points and resistance values). A visual inspection for obvious damage is the first step.
* Ignition Control Module (ICM): The ICM controls the ignition coil. A faulty ICM can prevent spark. These are often difficult to test without specialized equipment, but visual inspection for damage is a good start. Replacement is often the solution if suspected.
* Distributor (if applicable): While the Vortec 5700 technically uses a distributorless ignition system (DIS), some modifications or unusual configurations might involve a distributor. If present, check the cap, rotor, and the pickup coil inside for wear or damage. Inspect the wiring connections too.
* Ignition Switch: A faulty ignition switch won't send power to the rest of the ignition system. Check that the switch is providing power when the key is in the "on" or "start" position.
* Cranking System: If the engine isn't cranking, there won't be spark. Check the battery, cables, starter motor, and related wiring. A weak battery may not provide enough power to energize the system.
2. Wiring and Connectors:
* Wiring Harnesses: Look for broken, frayed, or corroded wires, especially those leading to the coil, ICM, and distributor (if applicable). Pay close attention to areas prone to chafing or damage.
* Connectors: Inspect all connectors for corrosion, loose connections, or broken pins. Clean and/or repair as needed.
3. Sensors:
* Crankshaft Position Sensor (CKP): This sensor tells the ICM when to fire the coil. A faulty CKP will prevent spark. It can often be tested with a multimeter, but you'll need to consult a wiring diagram for your specific vehicle.
* Cam Position Sensor (CMP): Similar to the CKP, a faulty CMP will interrupt the signal to the ICM.
4. PCM (Powertrain Control Module):
* The PCM controls many aspects of the ignition system. A faulty PCM is less likely, but it's possible. Diagnosing PCM issues usually requires specialized tools and expertise.
Troubleshooting Steps:
1. Visual Inspection: Start by thoroughly inspecting all components, wiring, and connectors for obvious damage.
2. Check for Power: Use a test light or multimeter to check for power at the coil and other ignition components.
3. Basic Tests: Perform basic resistance tests on the coil and other components using a multimeter. Refer to a wiring diagram or repair manual for specific resistance values.
4. Advanced Diagnostics: If basic tests don't reveal the problem, more advanced diagnostic tools might be necessary, such as a scan tool to check for diagnostic trouble codes (DTCs) stored in the PCM.
Important Considerations:
* Repair Manual: A factory repair manual for your specific year and model GMC is invaluable for troubleshooting and testing procedures.
* Safety: Disconnect the negative battery terminal before working on any electrical components.
* Professional Help: If you're not comfortable working on your vehicle's electrical system, it's best to take it to a qualified mechanic. Misdiagnosis can lead to further damage.
By systematically checking these components and using appropriate testing methods, you should be able to pinpoint the cause of the no-spark condition in your GMC. Remember safety first!
