1. Ignition System - The Most Likely Culprit:
* Coil: The ignition coil is a common failure point. It transforms low-voltage battery power into the high voltage needed for spark. Test it with a multimeter (check your owner's manual or online for specific instructions for your coil). A failing coil often exhibits intermittent performance before complete failure.
* Ignition Module (or Control Unit): This component controls the ignition coil's firing. A faulty module can prevent spark entirely or cause inconsistent sparking. These are often difficult to test without specialized equipment; replacement is often the easiest route if you suspect this.
* Distributor Cap and Rotor: These components distribute the high voltage to the spark plugs. Check for cracks, burns, or corrosion on the cap and rotor. Replace them if anything looks amiss – they're relatively inexpensive. Make sure the rotor is correctly aligned with the distributor cap.
* Spark Plugs and Wires: Inspect the spark plugs for fouling (soot buildup) or damage. Check the spark plug wires for cracks, fraying, or loose connections. Replace as needed.
* Ignition Switch: While less likely, a faulty ignition switch can prevent power from reaching the ignition system.
2. Crank Position Sensor (If Equipped): While less common in '87 Wranglers, some may have a crank sensor. This sensor tells the ignition system when to fire the spark. A bad sensor can lead to no spark.
3. Other Potential Issues (Less Likely, But Possible):
* Battery and Cables: A weak battery or corroded battery cables can prevent enough power from reaching the ignition system. Check the battery voltage and cable connections.
* Alternator: While a failing alternator won't directly cause a lack of spark, a completely dead battery (due to alternator failure) will. Test the alternator's output.
Troubleshooting Steps:
1. Start with the easy stuff: Check the battery voltage, cables, and visually inspect the distributor cap, rotor, spark plug wires, and plugs.
2. Test for Spark: The easiest way to check for spark is to remove a spark plug wire, ground the metal end of the wire to a grounded metal part of the engine (be careful!), and crank the engine. You should see a bright blue spark. If not, the problem is somewhere in the ignition system.
3. Systematic Elimination: Once you've visually inspected the easy parts, start testing components – the coil and then the ignition module. You'll likely need a multimeter for this.
Important Note: Working on an ignition system involves high voltage that can be dangerous. Be careful and disconnect the negative battery cable before working on any ignition system components. If you're not comfortable working with electricity, take it to a qualified mechanic.
