Variable Reluctance Sensor (VRS)

The VRS is used on 4.0L Electronic Distributorless Ignition System (EDIS). The VRS transmits crankshaft position and RPM information. It is a passive electromagnetic device sensing movement of a 35-tooth wheel with a gap for triggering where the 36th tooth would be. It is located behind crankshaft pulley. The missing tooth is at 60° BTDC.

The AC voltage signal, generated by VRS, increases with engine RPM and provides information to EDIS ignition module. Ignition module uses this input to produce a PIP signal to ECA. The ECA responds with a Spark Angle Word (SAW) signal, used by ignition module along with VRS signal to compute basic spark timing and determine which coil pack to trigger.