1. The Basics (Check these FIRST):
* Battery: Is the battery fully charged? Test the voltage with a multimeter. A weak battery can prevent sufficient power for the ignition system.
* Battery Connections: Are the battery terminals clean and tight? Corrosion can significantly impede current flow. Clean them with a wire brush and baking soda solution.
* Grounds: Poor grounding can prevent proper electrical flow. Check all ground straps (especially the one from the engine to the chassis) for corrosion and tightness.
2. Ignition System Components:
* Ignition Switch: Try wiggling the ignition key while in the "start" position. A faulty ignition switch can interrupt power to the rest of the system.
* Ignition Coil: This component transforms low voltage from the battery into the high voltage needed for spark. You can test it with a multimeter (check your vehicle's repair manual for the correct procedure). A visual inspection might show cracks or damage. A bad coil is a common culprit for no spark.
* Ignition Control Module (ICM): (Often integrated with the distributor on some models) This module controls the ignition timing. Testing this component usually requires a multimeter and some specialized knowledge.
* Distributor Cap and Rotor: Inspect these for cracks, corrosion, or excessive wear. A faulty cap or rotor will prevent proper spark distribution to the spark plugs. Replace them if they look damaged.
* Spark Plugs and Wires: Check the spark plugs for wear and fouling. Also, inspect the spark plug wires for cracks, fraying, or damage. A visual inspection is a good first step. A spark tester can definitively check if each wire is delivering a spark.
* Distributor: If you have a distributor, ensure it's properly seated and the mechanical advance mechanism is functioning correctly (if applicable).
3. Testing for Spark:
The most crucial step is to verify if you have any spark at all. Use an inline spark tester or even a spare spark plug wired to a wire (be careful!) Ground the plug's metal threads to the engine block. Then crank the engine. If you see a strong blue spark, the problem lies downstream (spark plugs or wires). No spark indicates an issue with the ignition coil, ICM, distributor, or ignition switch.
4. Additional Considerations:
* Fuel Pump Relay: While you're looking for spark issues, a failed fuel pump relay might prevent starting even if you have a spark; the engine needs fuel to run.
* Security System: If your truck has an aftermarket security system, it could be disabling the ignition system.
* Previous Repairs: Were any recent repairs done to the electrical system or ignition?
5. Getting Help:
If you're uncomfortable performing these tests, take your K5 Blazer to a qualified mechanic. Incorrect testing could damage components. A repair manual specific to your 1987 K5 Blazer will provide detailed wiring diagrams and testing procedures.
Remember to always disconnect the negative battery terminal before working on any electrical components to avoid injury. Safety first!
