System Description: Description

Deceleration fuel shut-off control is performed when the following conditions are satisfied.

• Engine is running
• Driving the vehicle
• When accelerator pedal is not depressed
• Selector lever is in D or R range
• ASCD mode: OFF
• Exhaust gas temperature: within specified value

Deceleration fuel shut-off control has advantages as follows.

• Improving engine brake effort
• Improving fuel efficiency
• Reduction in toxic exhaust gas

ECM controls the deceleration fuel shut-off according to the following sensors and signals.

• Engine coolant temperature sensor
• Accelerator pedal position sensor (Accelerator pedal position)
• Crankshaft position sensor (Engine speeds)
• TCM (Shift position)

When decelerating with the accelerator pedal not depressed, ECM turns OFF the fuel injector according to coolant temperature, shift position, and engine speed. In addition, ECM adjusts valve overlap to the minimum via intake camshaft actuator and exhaust camshaft actuator. This reduces toxic exhaust gas. After deceleration fuel shutoff control, ECM extends the injection time and temporarily controls air-fuel mixture to the rich side to remove excess oxygen from the catalyst addition, ECM adjusts ignition timing in retard direction to prevent a rapid torque increase when the combustion is restarted.

If exhaust gas has high oxygen content during deceleration, the catalyst may overheat due to accelerated oxidation of carbon monoxide and carbon hydrate. For this reason, ECM does not perform deceleration fuel shutoff control when exhaust gas temperature is too high.