Fuel and Emissions Systems

System Descriptions (cont'd)

11-23  

Idle Control System

When the engine is cold, the A/C compressor is on, the transmission is in gear, the brake pedal is pressed, the power steering load is high, or the alternator is charging, the ECM controls current to the Idle Air Control (IAC) valve to maintain the correct idle speed. Refer to the System Diagram to see the functional layout of the system.

Brake Pedal Position Switch

The brake pedal position switch signals the ECM when the brake pedal is pressed.

Electrical Power Steering (EPS) Signal

The EPS signals the ECM when the power steering load is high.

Idle Air Control (IAC) Valve

To maintain the proper idle speed, the IAC valve changes the amount of air bypassing the throttle body in response to an electrical signal from the ECM.

Fuel Supply System

Fuel Cut-off Control

During deceleration with the throttle valve closed, current to the injectors is cut off to improve fuel economy at speeds over 1,200 rpm (min-1). Fuel cut-off action also occurs when engine speed exceeds 8,100 rpm (min-1), regardless of the position of the throttle valve, to protect the engine from over-revving. When the vehicle is stopped, the ECM cuts the fuel at engine speeds over 5,500 rpm (min-1).

Fuel Pump Control

When the ignition is turned on, the ECM grounds the PGM-FI main relay which feeds current to the fuel pump for 2 seconds to pressurise the fuel system. With the engine running, the ECM grounds the PGM-FI main relay and feeds current to the fuel pump. When the engine is not running and the ignition is on, the ECM cuts ground to the PGM-FI main relay which cuts current to the fuel pump.

PGM-FI Main Relay 1 and 2

The PGM-FI relay consists of two separate relays. The PGM-FI main relay 1 is energised whenever the ignition switch is ON (II) which supplies battery voltage to the ECM, power to the injectors and power for the PGM-FI main relay 2. The PGM-FI main relay 2 is energised to supply power to the fuel pump for 2 seconds when the ignition switch is turned ON (II), and when the engine is running.