24X and 7X CKP Sensors/Harmonic Balancer Interrupter Ring

24X And 7X Crankshaft Position Sensors/Harmonic Balancer Interrupter Ring:

The 24X Crankshaft Position (CKP) Sensor (1), secured in a mounting bracket (3) and bolted to the front side of the engine timing chain cover (2), is partially behind the crankshaft balancer.




The 7X CKP sensor uses a two wire connector at the sensor and a three-way connector at the ignition control module.

The 24X CKP sensor contains a Hall-effect switch. The magnet and Hall-effect switch are separated by an air gap. A Hall-effect switch reacts like a solid state switch, grounding a low current signal voltage when a magnetic field is present. When the magnetic field is shielded from the switch by a piece of steel placed in the air gap between the magnet and the switch, the signal voltage is not grounded. If the piece of steel (called an interrupter) is repeatedly moved in and out of the air gap, the signal voltage will appear to go on-off, on-off, on-off. Compared to a conventional mechanical distributor, this on-off signal is similar to the signal that a set of breaker points in the distributor would generate as the distributor shaft turned and the points opened and closed.

In the case of the electronic ignition system, the piece of steel is a concentric interrupter ring mounted to the rear of the crankshaft balancer. The interrupter ring has blades and windows that, with crankshaft rotation, either block the magnetic field or allow the field to reach the Hall-effect switch. The Hall-effect switch is called a 24X CKP sensor, because the interrupter ring has 24 evenly spaced blades and windows. The 24X CKP sensor produces 24 on-off pulses per crankshaft revolution.

The interrupter ring is a special wheel cast on the crankshaft that has seven machined slots, six of which are equally spaced 60 degrees apart. The seventh slot is spaced 10 degrees from one of the other slots. as the interrupter ring rotates with the crankshaft, the slots change the magnetic field. This will cause the 7X to ground the 3X signal voltage that is supplied by the ignition control module. The ignition control module interprets the 7X on-off signals as an indication of crankshaft position. The ignition control module must have the 7X signal to fire the correct ignition coil.

The 7X interrupter ring and Hall-effect switch react similarly. The 24X signal is used for better resolution at a calibrated RPM.