Engine and Emission Control System Description - Ignition Timing Control (Cont'd)

The ignition timing is controlled by the E.C.U. in order to maintain the best air-fuel ratio in response to every running condition of the engine. The ignition timing data is stored in the ROM located in the E.C.U., in the form of the map shown below.

The E.C.U. detects information such as the injection pulse width and crank angle sensor signal which varies every moment. Then responding to this information, ignition signals are transmitted to the power transistor. e.g. N: 1,800 rpm, Tp: 1.50 msec A °B.T.D.C.

In addition to this, 1) At starting 2) During warm-up 3) At idle 4) At acceleration the ignition timing is revised by the E.C.U. according to the other data stored in the ROM.

The retard system actuated by the detonation sensor is designed only for emergencies. The basic ignition timing is pre-programmed within the anti-knocking zone, even if recommended fuel is used under dry conditions. Consequently, the retard system does not operate under normal driving conditions.

However, if engine knocking occurs, the detonation sensor monitors the condition and the signal is transmitted to the E.C.C.S. control unit. After receiving it, the control unit retards the ignition timing to avoid the knocking condition.