Subaru Coupes/Sedans/Wagons 1985-1996 Repair Guide

General Information


See Figure 1

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Fig. Fig. 1: Schematic of a distributorless ignition system

A distributorless ignition system is used on all 2.2L and 2.5L models. The system consists of a cam and crankshaft angle sensor, knock sensor, two ignition coils, an Electronic Control Unit (ECU) and assorted sensors.

The system control features a quick response learning control method that compares data stored in the ECU memory to data received from the sensors. Thus, the ECU constantly provides the optimum ignition timing in relation to output, fuel consumption, exhaust gas and other variables.

The ECU receives signals from the airflow sensor, water temperature sensor, crank angle sensor, cam angle sensor, knock senor and other various indicators to judge the operating condition of the engine. It then selects the optimum ignition timing stored in the memory and immediately transmits a primary current OFF signal to the igniter to control the ignition timing.

The ECU also receives signals emitted from the knock sensor. Ignition timing is controlled so that advanced ignition timing is maintained immediately before engine knock occurs.

Two ignition coils are used, one for the No. 1 and No. 2 cylinders, and one for the No. 3 and No. 4 cylinders. A simultaneous ignition type is employed for each bank of cylinders. This eliminates the distributor and achieves maintenance free operation.

Ignition control under normal conditions is performed by the ECU measuring engine revolutions. Using the data it receives, the ECU decides the ignition timing according to engine operation. Ignition control under starting conditions is set by the ECU at 10° BTDC.