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RPM Reference Signal

WARNING: This page does not describe the selected car, but rather 10 other vehicles, including the 1994 GMC Yukon, 1994 GMC Suburban, 1994 GMC Pickup, 1994 GMC Cab & Chassis, and 1994 GMC C3500 HD. However, it is still accessible from the selected car via links, so may be relevant.

PCM 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 (2.2L and 3.8L). PCM uses signal to determine control of timing, fuel delivery (fuel pump relay energizing), EGR function and idle speed. PCM also uses signal to trigger fuel injectors.

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