The CMP (also know as the TDC or top dead center sensor) detects top dead center on the compression stroke for cylinders No. 1 and No. 4. The signal is used by the ECM to calculate fuel injection and ignition timing sequence. CMP sensors are used on vehicles equipped with both distributor and distributorless ignition. They are located either inside the distributor or attached to the cylinder head near the end of the camshaft.
See Figures 1 and 2
Camshaft position sensors for early model engines can be identified by a 4 terminal connector, while sensors for late model engines can be identified by a 3 terminal connector.
- Backprobe the sensor electrical harness with the ignition ON .
- Measure voltage between sensor terminals 1 and 3 (early model engines) or terminals 1 and 2 (late model engines) while cranking the engine around slowly.
- Voltage should alternate between 0-5.0 volts.
- If voltage does not alternate, check power and ground circuits.
- If power and ground circuits are functional, sensor is faulty.
REMOVAL & INSTALLATION
Distributor Mounted Sensor
Removal and installation of the distributor mounted CMP requires complete disassembly of the distributor. If the CMP is found to be faulty, it is recommended that the entire distributor be replaced as an assembly.Cylinder Head Mounted Sensor
- Disconnect the negative battery cable.
- Label and disconnect the sensor electrical harness
- If sensor mounting bolts have slots for adjustment, matchmark the sensor and the cylinder head.
- Loosen sensor mounting bolts.
- Carefully remove the sensor.
- Carefully install the sensor and tighten mounting bolts to 6 ft. lbs. (8 Nm).
- Connect the sensor electrical harness
- Connect the negative battery cable.
- If sensor mounting bolts have slots for adjustment, connect a timing light and adjust the ignition timing.