Jeep Cherokee Engines - Camshaft Position Sensor / Sync Pulse (Stator) Diagnostics

CAMshaft Position Sensor / Sync Pulse (Stator) Test

This article is intended to help you diagnose intermittant ignition problems that cannot be attributed to other sensors or the more failure prone Crankshaft Position Sensor. The CAM-shaft position sensor (aka 'stator' or sync pulse generator) lets the ECU know when to pulse the fuel injectors and co-ordinates with the Crankshaft Position Sensor for engine timing.

WARNING!: The term CPS is most often used to describe the CRANKshaft position sensor! Be SURE to get the correct sensor! Both the crank and cam position sensors work together feeding the ECU (computer) information on the engine timing to fire the injectors and maintain engine timing. In the case of the Jeep 4.0L engine: the CAMshaft position sensor is also called the 'sync pulse generator' (or stator) and can be found in the "distributor" while the CRANKshaft position sensor is located on the transmission bellhousing. (* See bottom of page.)

Don't be surprised if your counter drone tries to hand you the wrong part as there are several common names in use for the Camshaft Position Sensor:

camshaft position sensor
stator
sync-pulse generator
"...Auto Zone had the (sync signal generator) but they call it a pick-up coil..." (from a post at JU)

HO Distributor

HO Camshaft Position Sensor / Sync-Pulse Generator diagram. MUCH easier to access! No need to remove distributor drive gear.

The HO distributor has a MUCH easier to replace 'stator' than the RENIX engines. No need to remove the drive gear - the Camshaft Position Sensor (aka: stator or sync-pulse generator) is easily removed from the top once you remove the rotor from the distributor. If ya can't handle replacing the HO 'stator' then ya probably should keep away from butter knives and other complex technical items.

RENIX Distributor 1987 - 1990


This is an overhead shot of a RENIX Jeep distributor. The 'pulse ring' is the cover shown obscuring the stator itself. The stator mounts beneath this pulse ring. It is necessary to disassemble the distributor by pulling the drive gear to remove the pulse ring and then gain access to the stator.	This is a view of an aftermarket, OEM style replacement RENIX stator. No need to visit the dealer... these can be purchased at auto parts stores such as NAPA.

Stator Test Procedure

Sync Pulse (Stator) Test: Do NOT disconnect your "distributor" to do this test! Backprobe the connectors by inserting the voltmeter's probes into the connector where the wires enter the connector from the distributor or harness! You'll have to make sure that you have good contact but it's not hard to do... the connector MUST remain connected to do these tests!

Analog volt ohm meter... yes, you can still get them... and yes, you still use them in many applications where a digital meter would 'average out' any fluctuations you need to see visually.

While you can check the voltages and continuity with a digital volt meter... you will also need an ANALOG volt meter (with a needle... not digital readout) to check the stator's function.

RENIX TEST PROCEDURE

Insert + voltmeter lead into BLUE wire at distributor connector.
Insert negative - lead into Gray W/trace wire at dist connector.
Set voltmeter to 15vac, turn key on & should show approximately 5.0volts.
If there is no voltage present - double check the backprobed leads to ensure good contact.
If there is STILL no voltage present; the Factory Service Manual says you need to "Perform vehicle test using DRB II tester. I don't have one. You don't either.
At this point, If you DO have voltage then remove / disconnect the ECU (computer).
Check continuity between the Blue wire and C-16 at the ECU. - If no continuity: repair harness wire.
Check continuity between Gray W/trace and pin C-5 at the ECU. - If no continuity: repair harness wire.
Check continuity between Black wire and "ground". - If no continuity: repair harness wire.
While observing analog voltmeter (That's one with a needle, folks! Your average digital meter won't show this...) crank engine & voltmeter needle should fluctuate back & forth while engine is cranking over. This confirms stator in distributor is 'pulsing' correctly and sending signal out for ECU.
If there is no sync pulse you will have to replace the stator by removing and dissassembling the "distributor" following the service manual procedure. * - Helpful Hint: Before pulling your distributor... "bump" the engine until the rotor is pointing straight forward and aligned with the side of the engine. That way you'll know where the rotor needs to end up pointing after reassembly.

Was it bad?

If your stator tested bad then Click Here to Replace Your Faulty RENIX Camshaft Position Sensor.

WARNING!: The term CPS is most often used to describe the CRANKshaft position sensor! Be SURE to ask for the correct sensor! Both the crank and cam position sensors work together feeding the ECU (computer) information on the engine timing to fire the injectors and maintain engine timing. In the case of the Jeep 4.0L engine: the CAMshaft position sensor is also called the 'sync pulse generator' (or stator) and can be found in the "distributor" while the CRANKshaft position sensor is located on the transmission bellhousing.

CRANKshaft position sensor ... this is NOT the CAMshaft position sensor.

Do Not Confuse the CAMSHAFT position sensor with the CRANKSHAFT Position Sensor (CPS... aka: CKP) shown above!
Make sure your counterdrone knows which one you are after!
Look at bottom of THIS LINK for CRANKSHAFT Position Sensor Information.

CRANKSHAFT Position Sensor (CPS... aka: CKP) is located on the transmission bellhousing!
Make sure your counterdrone knows which one you are after!
Look at bottom of THIS LINK for CRANKSHAFT Position Sensor Information.

If you have pics of your own repairs or can suggest other methods - please contribute your ideas (and pictures) to this article!

Revised on: June 6th, 2007