Oct 162017
 

Jeep Cherokee

Recently it started stalling out in traffic, but would start right back up no problem. Then stalls back out a few more miles down the road but again start right back up. The sensors check out fine, coil checks out fine, replaced the cam sensor that the on board computer says was bad. It is still stalling out but only in drive never at an idle. The only thing I can find wrong is only getting 9.4 volts to sensors the cam and the crank.


Generally when the computer sets a code for the cam position sensor it goes into default mode. This means it uses preset parameters to allow the engine to continue to run. The most common reason for the issue you have described would be a failing ignition control module. However the functions of the ignition control module are performed by the Electronic Control Unit (ECU), also known as the Powertrain Control Module. You stated that you already tried replacing it. My first thoughts would be if it was a reman unit from Autozone, you might want to take it back and try another one.

Next thought since you stated a lower than normal voltage reading that there might be an issue with the wiring harness. Maybe looking the harness over for any breaks or rubbing. Or even going more in-depth and performing a continuity test on each wire.

Camshaft Position Sensor Operation – 1993 Jeep Cherokee 4.0L

The Camshaft Position Sensor, or CMP sensor is located inside the distributor. The PCM uses the CMP signal to determine the position of the No. 1 cylinder piston during its power stroke. The PCM uses this information in conjunction with the crankshaft position sensor to determine spark timing among other things.

The CMP sensor contains a Hall effect device which sends either a 0.0 volt or a 5.0 volt signal to the PCM depending on the position of the distributor shaft.

If the cam signal is lost while the engine is running, the PCM will calculate spark timing based on the last CMP signal and the engine will continue to run. However, the engine will not run after it is shut off.

camshaft position sensor location diagram Jeep Cherokee

Hall-effect CMP Testing

1.Connect a scan tool to the data link connector (DLC) and check the CMP sensor datastream for a normal waveform.
2.If the scan tool waveform for the CMP sensor is not within the specified values perform a visual inspection on the CMP sensor, wiring harness, connector and related components as follows: ◦Ensure that the connector tabs are fully locked
◦Check for corroded terminals
◦Bent pins
◦Pins pulled back in the connector
◦Terminal cavities spread open
◦Harness damage
◦Sensor damage
◦Mounting

3.If the connectors, wiring harness and related mechanical components pass inspection, perform the following procedures to test the CMP sensor, wiring and related modules: A.Disconnect the CMP sensor connector.
B.Check the CMP power input circuit by performing a circuit resistance test between the CMP sensor and the power input. Use the Component Pin Data for circuit details.
C.Check the MAF sensor signal circuit to the PCM by performing a circuit resistance test between the MAF sensor and the PCM. Use the Component Pin Data for circuit details.
D.Check the MAF sensor ground circuit between the MAF sensor and PCM by performing a circuit resistance test. Use the Component Pin Data for circuit details.
E.Repair/replace defective parts as needed and recheck the scan data.

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