RPM Reference Signal

ECM monitors RPM through ignition module tach/pulse signals (on circuit No. 430) produced by the HEI module (RPM reference line of 4-wire EST connector) or Hall Effect camshaft and crankshaft sensors (3.8L). ECM uses signal to determine control of timing, fuel delivery (fuel pump relay energizing), EGR function and idle speed. ECM also uses signal to trigger fuel injectors.