* Ignition System:
* Spark Plug Wires: Did you reconnect the spark plug wires correctly? Even a single wire misconnected will prevent the engine from firing. Double-check that each wire is firmly attached to the correct spark plug and distributor cap terminal. Look for any cracks or damage in the wires.
* Distributor Cap and Rotor: Inspect the distributor cap and rotor for cracks, burns, or corrosion. These components can degrade over time and prevent proper spark distribution.
* Ignition Coil: A faulty ignition coil won't produce the high voltage needed to fire the spark plugs. Testing the coil requires a multimeter and some knowledge of automotive electrical systems.
* Ignition Module (or Control Unit): This is the "brain" that controls the ignition system. A malfunctioning module will prevent the coil from firing properly. Testing this is usually best left to a mechanic.
* Crank Position Sensor (CPS): This sensor tells the ignition system when to fire the spark plugs. A faulty CPS will prevent starting.
* Fuel System:
* Fuel Pump: While less likely immediately after a simple oil/plug change, a weak or failing fuel pump can prevent fuel from reaching the engine. You should hear the pump whirring for a few seconds when you turn the key to the "on" position (before cranking). If you don't hear it, that's a strong suspect.
* Fuel Filter: A clogged fuel filter restricts fuel flow. It's relatively inexpensive and easy to replace.
* Fuel Injectors (if equipped): While less common on an '88 Cherokee (they might have a carburetor), if it has fuel injection, clogged or faulty injectors could be the problem.
* Fuel Pressure: Low fuel pressure will prevent the engine from starting. This requires a fuel pressure gauge to check.
* Other Possibilities (less likely but worth considering):
* Timing Belt (or Chain): If the timing belt slipped or broke during the oil change (highly unlikely but possible if it was already worn), the engine won't start. This is a major problem requiring a mechanic.
* Security System (if equipped): Some vehicles have immobilizers that prevent starting if they detect a problem. This is less likely given the strong cranking.
Troubleshooting Steps:
1. Reconnect everything: Begin by meticulously checking all spark plug wires, ensuring they are securely connected to the correct terminals.
2. Inspect the distributor cap and rotor: Look for any visible damage.
3. Listen for the fuel pump: Turn the key to "on" (but don't crank) and listen for the fuel pump whirring.
4. Check for spark: With the spark plug wires disconnected, carefully ground each plug to the engine block and crank the engine. You should see a spark. (Caution: Be careful not to shock yourself).
If you're not comfortable performing these checks, it's best to take the vehicle to a mechanic. Trying to diagnose these issues without proper tools and knowledge can lead to further damage or injury.
