Rpm Reference Signal

The RPM is monitored by ECM through ignition module tach/pulse signals (on circuit No. 430) produced by the HEI module (RPM reference line of 4-wire EST connector) or camshaft position sensor signal (Hall Effect signal on 2.5L). Signal is used by ECM for determining control of timing, fuel delivery, EGR function and idle speed. Signal is used by ECM to trigger fuel injectors.