* Crankshaft Position Sensor (CKP): While you mentioned replacing the pickup coil (which *is* often the crankshaft position sensor in these vehicles), there might be a second CKP sensor on your specific Jeep Cherokee model or the replacement might be faulty. The CKP sensor is crucial because it tells the PCM (Powertrain Control Module) when to fire the spark. A faulty CKP prevents the PCM from sending the signal to the ignition module. Double-check its location and ensure it's correctly installed and functioning.
* Camshaft Position Sensor (CMP): Some Jeep Cherokees, particularly those with specific engine types (like the 4.0L), use a CMP sensor in addition to the CKP. This sensor tells the PCM the position of the camshaft, critical for timing the spark. A malfunctioning CMP can prevent the engine from starting even if the CKP is working.
* Ignition Control Module (ICM): This module receives the signals from the sensors and then sends the signal to fire the coil. A faulty ICM can prevent spark entirely. Though less common after replacing the coil, it's still a possibility.
* Wiring: Inspect all the wiring related to the ignition system, from the sensors to the ICM and coil. Look for broken wires, corrosion, loose connections, or damage from rodents. A simple break in the wiring can completely interrupt the signal. Pay close attention to the connections at the distributor, as these can be prone to problems.
* Distributor Cap and Rotor: Even with a new coil and pickup, a faulty distributor cap or rotor can prevent spark. Check for cracks, corrosion, or worn contacts in these components. They are inexpensive and should be checked/replaced as a matter of routine during this kind of troubleshooting.
* PCM (Powertrain Control Module): In rare cases, a problem with the PCM can prevent the spark signal from being sent. This is less likely but could be a factor if all other components are verified as good. This is usually diagnosed via a scan tool by a mechanic.
Troubleshooting Steps:
1. Verify CKP Sensor Function: Use a multimeter to check the CKP sensor's output signal while cranking the engine. Consult a repair manual for your specific Jeep Cherokee model to find the correct testing procedure and expected values.
2. Check CMP Sensor (if equipped): Similar to the CKP, test the CMP sensor's output signal using a multimeter. Again, consult a repair manual.
3. Inspect Wiring: Meticulously examine all wiring related to the ignition system. Look for any signs of damage, corrosion, or loose connections.
4. Inspect Distributor Cap and Rotor: Replace these even if they *look* okay. They are cheap enough to replace that the time saved versus additional testing is worth it.
5. Check ICM (Ignition Control Module): This usually requires testing with a multimeter. Consult a repair manual or a trusted automotive electrical diagnostic guide.
6. Professional Diagnosis: If you're not comfortable testing these components, take the Jeep to a mechanic. They have the tools and expertise to diagnose the problem more accurately. A scan tool can help rule out PCM problems or other electrical gremlins.
Remember safety first. Disconnect the negative battery cable before working on any electrical components. A repair manual specific to your Jeep Cherokee's year and engine will be incredibly helpful in this process.
