RPM Reference Signal

The RPM is monitored by ECM through ignition module tach/pulse signals (circuit No. 430) produced by either the HEI module (tach reference line of 4-wire EST connector) or crankshaft position sensor signal (Hall Effect signal on C(3)I, PM generator signal on DIS and IDI). These signals are used by ECM for determining control of timing, fuel delivery, EGR function and idle speed.