* Compression: Low compression in one or more cylinders prevents the fuel-air mixture from igniting properly. A compression test is crucial to diagnose this. Worn piston rings, valve problems, or a head gasket leak are common causes.
* Timing: The ignition timing might be significantly off. The spark plugs might be firing at the wrong time relative to the piston position, preventing combustion. A timing light is needed to check this.
* Crankshaft Position Sensor (CKP sensor): This sensor tells the computer the crankshaft's position to determine when to fire the spark plugs. A faulty CKP sensor will prevent the engine from starting.
* Camshaft Position Sensor (CMP sensor): Similar to the CKP sensor, but this one monitors the camshaft. A faulty CMP sensor can cause starting issues.
* Engine Control Module (ECM): The ECM controls fuel delivery and ignition timing. A faulty ECM can cause a variety of problems, including no start, even with fuel and spark. This is less likely but possible.
* Wiring and Connections: A problem with the wiring harness, particularly corroded connections, can interrupt the signal to the fuel injectors or ignition system. Check all connections, especially those near the distributor and ECM.
* Distributor: While you say you have spark, check the rotor and cap inside the distributor for wear or damage. A faulty distributor could provide weak or inconsistent spark.
Troubleshooting Steps:
1. Compression Test: This is the most important first step. Low compression points directly to a serious mechanical issue.
2. Timing Check: Use a timing light to verify ignition timing.
3. Check Sensors: Inspect the CKP and CMP sensors for damage. You might be able to test them with a multimeter (consult a repair manual for specifics).
4. Inspect Wiring and Connections: Look for any corrosion, broken wires, or loose connections.
5. Examine the Distributor: Check the cap and rotor for wear.
Without a proper diagnostic procedure, it's difficult to pinpoint the exact cause. A repair manual specific to your 1994 Jeep Wrangler 4-cylinder will be invaluable in helping you troubleshoot and test these components. If you're not comfortable working on your vehicle, taking it to a mechanic is recommended.
