1. The Basics:
* Battery: Check the battery voltage with a multimeter. It should be around 12.6V when fully charged. A weak battery can prevent starting, even if it cranks slowly. Test the battery and charging system (alternator).
* Starter: While you say it cranks, ensure the cranking is strong and consistent. A weak starter can sometimes crank slowly enough to prevent ignition.
* Grounds: Poor ground connections can disrupt electrical flow. Check the battery ground cable and engine block ground. Clean any corrosion.
2. Ignition System:
* Spark: This is crucial. Remove a spark plug wire, attach a spark plug to it, ground the plug to the engine block, and crank the engine. Look for a strong, blue spark. If no spark:
* Ignition Coil: Check the ignition coil for cracks or damage. A weak coil won't produce a strong spark.
* Ignition Control Module (ICM): The ICM controls the ignition coil. Failure is common in these Jeeps.
* Cranking Sensor (CMP): This sensor tells the computer the engine is turning. A faulty CMP will prevent spark.
* Distributor (if equipped): Inspect the distributor cap and rotor for cracks, corrosion, or worn contacts. Replace if necessary.
* Ignition Switch: A faulty ignition switch might not be sending power to the ignition system.
* Wiring: Check all ignition-related wiring for damage, corrosion, or loose connections.
3. Fuel System:
* Fuel Pump: Listen carefully for the fuel pump whine when you turn the ignition key to the "on" position (before cranking). You should hear a brief hum. If not, the pump might be bad or have a faulty relay.
* Fuel Pressure: This requires a fuel pressure gauge. The pressure should be within the specifications listed in your repair manual.
* Fuel Filter: A clogged fuel filter can restrict fuel flow.
* Fuel Injectors: While less likely to cause a no-start without other symptoms (like rough running), faulty injectors can be a problem. A fuel pressure test often catches injector problems indirectly.
4. Sensors:
* Crankshaft Position Sensor (CKP): Like the CMP, a faulty CKP prevents the computer from knowing the engine's position and timing ignition properly.
* Throttle Position Sensor (TPS): A faulty TPS might prevent the computer from allowing fuel injection.
5. Computer/PCM:
* While less common as the initial cause, a faulty PCM (Powertrain Control Module) can prevent the engine from starting. This is usually diagnosed after checking everything else.
Troubleshooting Steps:
1. Start with the basics (battery, grounds, starter).
2. Check for spark. This is a critical test.
3. Check fuel pump operation.
4. Consult a Jeep Cherokee 4.0L repair manual for wiring diagrams, specifications, and troubleshooting information. A Haynes or Chilton manual can be helpful.
5. If you're not comfortable working on the vehicle yourself, take it to a qualified mechanic.
Remember safety first! Disconnect the negative battery cable before working on any electrical components. If you are not experienced working on cars, seek professional assistance to avoid further damage.
