Spark Control Systems Diagnosis & Testing

Fig. 16 Deceleration spark advance system:

Fig. 19b Air Switching Valve System:

Fig. 18a Coasting Air Valve System:

1. Operate engine at idle speed, then disconnect wire connector from solenoid valve. If engine idle speed drops excessively or engine stalls, the solenoid valve and air switching valve operation is satisfactory. If idle speed remains unchanged, check for clogged vacuum passage and also check condition of solenoid valve and air switching valve.
2. With engine at idle speed, battery voltage should be present at the solenoid valve wire connector. If battery voltage is not present, check wiring and engine speed sensor.
3. Increase engine speed to 1500 RPM and check for battery voltage at solenoid valve wire connector. If battery voltage is not present, the engine speed sensor is defective.
4. Increase engine speed to 2500 RPM and check to ensure that no voltage is present at solenoid valve wire connector. If voltage is present, the engine speed sensor is defective.

Fig. 17 Dashpot adjustment: