1. Safety First!
* Disconnect the negative battery cable before starting any electrical work. This prevents accidental shorts and shocks.
2. Check the Basics:
* Battery Voltage: Use a multimeter to check the battery voltage. It should be around 12.6V when not charging. A weak battery can cause intermittent or no spark.
* Fuses and Relays: Inspect the fuses and relays related to the ignition system. Your owner's manual will show you the fuse box layout and which fuses/relays are relevant. The ignition system often has its own relay. Look for blown fuses (broken filament) and relays that are clicking erratically or not clicking at all.
* Ignition Switch: Try turning the key to the "ON" position (without starting) and check for power at the ignition coil (positive side). If no power here, suspect the ignition switch itself or a wiring problem between the switch and the coil.
3. Ignition System Components (in order of testing):
* Crankshaft Position Sensor (CKP): This sensor tells the PCM (Powertrain Control Module) the position of the crankshaft so it knows when to fire the spark. A faulty CKP will prevent any spark. You'll need to find the CKP sensor location (usually near the crankshaft), disconnect it, and check for continuity with a multimeter according to the specifications in your repair manual. Also check for any damaged wires leading to the sensor.
* Camshaft Position Sensor (CMP): Similar to the CKP, a faulty CMP will also prevent spark. Locate the CMP sensor, disconnect it, and check for continuity with a multimeter according to your repair manual. Inspect wiring as well.
* Ignition Control Module (ICM): The ICM is a common point of failure. It receives signals from the sensors and sends the signal to fire the coil. Testing this component often requires a multimeter and understanding the resistance and voltage specifications (found in a repair manual). A simple visual inspection for obvious damage is also a good first step.
* Ignition Coil: While less likely to be the *sole* cause if you have no spark at the coil itself, a faulty coil can prevent spark. You can check for resistance with a multimeter according to the specifications in your repair manual. Visually inspect for cracks or damage.
* Ignition Wires: Inspect the ignition wires for cracks, fraying, or damage. A broken or damaged wire can interrupt the spark.
4. PCM (Powertrain Control Module):
This is the "brain" of your engine. A faulty PCM *can* cause a no-spark condition, but it's usually a last resort. PCM testing usually requires specialized diagnostic equipment, and often a replacement is necessary if faulty.
5. Using a Diagnostic Tool:
An OBD-II code reader can be invaluable. It will read any diagnostic trouble codes (DTCs) stored in the PCM, which can provide clues to the problem.
Important Notes:
* Repair Manual: A factory service manual or a Chilton's/Haynes repair manual is essential for detailed information on testing procedures, wiring diagrams, and component specifications. These manuals will provide resistance and voltage specs, connector locations, and troubleshooting steps specific to your 1997 Chevy Blazer 4.3L V6.
* Professional Help: If you're not comfortable working with automotive electrical systems, it's best to seek the help of a qualified mechanic. Improper testing can damage components.
Start with the simpler checks (battery, fuses, relays, visual inspection of wires) and work your way through the components. Keep track of your findings. The process of elimination is key to diagnosing this type of problem.
