Slow Fuel Cut System Mazda 626 GC

DESCRIPTION

The Slow Fuel Cut system is used to seal the primary slow fuel passage of the carburetor to prevent "dieseling" and overheating of exhaust system. It is part of the Computerized Engine Control system.

Components of the system include the slow fuel cut solenoid valve, neutral switch, clutch switch (M/T), idle switch and necessary electrical connections.

Mazda 626 models also incorporate a Coasting Richer System in the Slow Fuel Cut System. The Coasting Richer System opens the carburetor secondary stage fuel line during deceleration.

Slow Fuel Cut & Coasting Richer System (626). Scheme 14

The slow fuel cut solenoid valve seals the primary slow fuel passage of the carburetor when the ignition is turned off or when all components of the system are off. (Scheme 15)

COASTING RICHER SYSTEM

The coasting richer solenoid valve in the carburetor opens the secondary fuel passage. Solenoid operation is governed by the Control Unit. The Control Unit uses data from the ignition coil, neutral and clutch switches and idle switch to control the solenoid valve. (Scheme 16)

View of Coasting Richer System Coasting richer system is used on 626 models only. Scheme 15

Scheme 16

1. Bring engine to operating temperature and run at idle speed. Disconnect neutral switch connector. Connect a voltmeter to Light Green terminal of check connector. Reading should be below 1.5V. (Scheme 16) (Scheme 16): Testing Slow Fuel Cut System Attach voltmeter to Light Green terminal.
2. Connect tachometer to engine. Increase engine speed to above 3000 RPM, and decelerate rapidly. During deceleration, voltmeter should read approximately 12V above 2000 RPM and less than 1.5V below 2000 RPM.

Solenoid Valve

Run engine at idle and disconnect slow fuel cut solenoid valve connector. If engine stops, solenoid valve is working properly.

Idle Switch (626 Models)

1. Bring engine to operating temperature and run at idle. Connect tachometer to engine. Disconnect electrical connector from switch. Connect positive voltmeter lead to Light Green/Black switch terminal, connect negative to Light Green/Red terminal.
2. Increase engine speed to above 2000 RPM and decelerate gradually. During deceleration, voltmeter should read below 1.5V when engine speed is above 1200 RPM and 12V when below 1200 RPM. Turn adjusting screw to obtain proper readings.

Clutch Switch (M/T Models)

1. Disconnect clutch switch electrical connector. Connect ohmmeter to switch terminals. Depress clutch pedal; continuity should exist.
2. Fully release clutch pedal; no continuity should exist. If switch does not operate as outlined, adjust or replace clutch switch.

Neutral Switch (M/T Models)

Raise and support vehicle. Disconnect neutral switch electrical connector. Connect ohmmeter to switch terminals. Continuity should exist when transmission is in Neutral and no continuity should exist in any other gear position. Replace neutral switch, if switch does not operate as outlined.

Neutral Switch (A/T Models)

1. Raise and support vehicle. Apply service brake and parking brake. Start engine and operate at idle. Disconnect electrical connector from switch. Connect ohmmeter to switch terminals.
2. Continuity should exist when transmission is in Neutral and no continuity should exist in any other gear position. Replace neutral switch, if it does not operate as outlined.

COASTING RICHER SYSTEM (626)

1. Bring engine to operating temperature and run at idle speed. Unplug neutral switch connector. Connect voltmeter to Brown/Black terminal of check connector. Voltmeter should register 12V.
2. Increase engine speed and push the idle switch button. Above 2000 RPM and below 1400 RPM, the voltmeter should read 12V. Between 1400 and 2000 RPM, the voltage should be 1.5V.

Run the engine at idle. Using jumper wire, ground check connector Brown/Black terminal. Engine speed should increase if valve is working properly.