Acura NSX 1991 Manual page 759

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Description
Ignition Timing Control:
The programmed ignition used in this engine provides optimum control of ignition timing. A microcomputer determines
the timing in response to engine speed and manifold vacuum pressure. The input signals are transmitted by the crank-
shaft position/cylinder position (CKP/CYP) sensor, throttle position (TP) sensor, ECT sensor, and MAP sensor. This sys-
tem, not dependent on a governor or vacuum diaphragm, is capable of setting lead angles with complicated characteristics
which cannot be provided by conventional governors or diaphragms.
Basic Control
Determination of ignition timing/current duration:
The ECM has stored within it the optimum basic ignition timing for operating conditions based upon engine speed and in-
take manifold pressure. With compensation by signals from sensors, the system determines optimum timing for ambient
conditions and sends voltage pulses to the ICM.
Compensation of Ignition Timing:
Control at Start
Ignition timing is fixed at 5° BTDC for cranking. The cranking is detected by the CYP sensor (cranking rpm) and starter signal.
Misfiring Detection
As part of the OBD II misfiring detection system, each of the ignition coil has a built-in spark plug voltage sensor. This
sensor detects the long duration high voltage which occurs in case of unfavorable combustion or misfiring. (For details,
see section 11.)
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