Stepper motor - ’T’ series

The position of the idle air control valve can be checked using TestBook and should be within the range of 20 to 40 steps when the engine is running. If it is identified as being outside this range it can be adjusted to within range using TestBook. This ensures that the idle air control valve is at the optimum position within its range for providing further movement to compensate for changes in engine load or temperature in accordance with signals from the ECM.

NOTE: The position of the throttle disc is preset during manufacture and the throttle position setting screw MUST NOT be adjusted.

Stepper motor - ’T’ series

The stepper motor is contained within the throttle housing and operates a cam and push rod via a reduction gear. The push rod is in direct contact with the throttle lever and moves the throttle disc to control idle and fast idle speed. The stepper motor has a maximum movement of 3.75 revolutions accomplished in steps of 7.5˚. The reduction gear converts this into 180˚ of cam movement.

The throttle lever has a throttle position setting screw which rests on the stepper motor operating pin when the throttle pedal is released and is used to set the relationship between engine speed and stepper motor position. In the side of the throttle housing is a throttle air bypass bleed screw to provide easier and more sensitive setting of the stepper motor position at idle.

The stepper motor position is checked using TestBook and should be within the range of 20 to 40 steps when the engine is run in. If it is identified as being outside this range it can be adjusted to within range by turning the throttle air bypass bleed screw. It is important to follow the TestBook setting procedure when adjusting this screw to prevent mismatching of throttle body settings. This ensures that the stepper motor is at the optimum position within its range for providing further movement to compensate for changes in engine load or temperature in accordance with signals from the ECM.

NOTE: The stepper motor and throttle position setting screws must only be adjusted when TestBook identifies the requirement.

Relay module

The relay module is located on bulkhead in the engine compartment behind the engine control module. The relay module contains the following relays:

• Main relay - energised when the ignition is switched on and supplies power to the ECM.
• Fuel pump relay - energised by the ECM for a short period when the ignition is switched on, during cranking and while the engine is running.
• Starter relay - energised by the cranking signal from the ignition switch.
• Heated oxygen sensor relay - energised by the ECM and supplies current to the heated oxygen sensor element.

Fuel pump

The electric fuel pump is located inside the fuel tank and is energised by the ECM via the fuel pump relay in the relay module and the fuel cut-off switch.

The fuel pump delivers more fuel than the maximum load requirement for the engine, pressure is therefore maintained in the fuel system under all conditions.

Fuel pressure regulator

The pressure regulator is a mechanical device controlled by manifold depression and is mounted on one end of the fuel rail. The regulator ensures that fuel rail pressure is maintained at a constant pressure difference to that in the inlet manifold, as manifold depression increases the regulated fuel pressure is reduced in direct proportion.

When pressure exceeds the regulator setting, excess fuel is returned to the fuel tank swirl pot which contains the fuel pump pick-up.