Circuit Description

PCM uses spark reference signal circuit to improve ignition timing accuracy during crank and at engine speeds up to 1200 RPM. Spark reference circuit allows use of ignition control mode at speeds less than 400 RPM, eliminating need to utilize module mode during start-up, and also allows PCM to calculate true crankshaft position in 1/6 the time that use of fuel control reference signal would permit.

During normal operation, PCM uses spark reference signal to control ignition timing until engine speed exceeds 1200 RPM, at which time fuel control reference signal circuit is used.