1. Verify the Code:
* Get the exact code number(s). "Engine speed sensing circuit" is a general description. The specific code (e.g., P0335, P0336, etc.) will pinpoint the exact sensor or circuit malfunction more precisely.
* Clear the codes. After addressing potential problems, clear the codes to see if the issue recurs. This helps differentiate between intermittent and persistent faults.
2. Focus on the Crankshaft Position Sensor (CKP):
* Locate the CKP sensor. Consult your Jeep's repair manual (a Chilton's or Haynes manual is helpful) to find its exact location. It's usually on the engine block near the crankshaft pulley.
* Visually inspect the sensor. Look for any obvious damage, corrosion, loose connectors, or broken wiring.
* Check the wiring harness. Carefully inspect the wiring from the sensor to the PCM (Powertrain Control Module) for any breaks, chafing, or damage. Pay close attention to the connector itself.
* Test the sensor (advanced step). This requires a multimeter and a bit of electrical knowledge. The procedure varies depending on the sensor type. Your repair manual or online resources (like YouTube tutorials) will show you how to check for continuity and signal output.
* Replace the CKP sensor. If the sensor is suspect, replacing it is relatively inexpensive and often solves the problem. Make sure you get a sensor that's the correct part number for your specific engine.
3. Other Potential Culprits (less likely but worth checking):
* Cam Position Sensor (CMP): While the code points to the CKP, a faulty CMP can also cause similar symptoms. It's worth inspecting this sensor and its wiring as well.
* Ignition Control Module (ICM): A malfunctioning ICM can disrupt the ignition timing, leading to erratic engine behavior.
* PCM (Powertrain Control Module): In rare cases, a faulty PCM can cause these symptoms. This is the most expensive component to replace and should only be considered after other possibilities have been eliminated.
* Wiring harness connectors: Look for corrosion or poor connections in all connectors related to the engine control system.
* Battery voltage/charging system: Low voltage can cause intermittent issues.
4. Fuel System Considerations:
* The fact that injectors continue firing after key-off suggests a problem with the fuel pump relay or a short circuit somewhere in the fuel system that's preventing the injectors from shutting off properly.
Important Safety Precautions:
* Disconnect the negative battery terminal before working on any electrical components.
* Be cautious when working around hot engine parts.
* Use proper safety glasses and gloves.
Recommendation:
Start with the CKP sensor. It's the most likely culprit based on the code and symptoms. If replacing the CKP doesn't fix the problem, then systematically investigate the other possibilities, starting with the CMP and wiring harnesses. A repair manual is crucial for detailed instructions and diagrams. If you're not comfortable with auto repair, take it to a qualified mechanic.
