Air Management: Notes

Fig 1: Identifying Air Management System

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Throttle Valves: The mechanical throttle valves regulate the intake air flow and are operated by an Electronic Throttle Actuator (1 EDR).

The throttle valves are an assembly of six individual throttle housings linked by a common shaft. The throttle opening depends on engine RPM and load (1000 kg/h maximum air flow).

Fig 2: Identifying Electronic Throttle Actuator

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Accelerator Pedal Position (PWG):

The accelerator pedal module provides two variable voltage signals to the ECM that represents accelerator pedal position and rate of movement. The ECM will activate the EDR and Idle Air actuator based on the request.

Dual Hall Sensors are integral in the accelerator pedal module. The ECM compares the two values for plausibility.

Fig 3: Identifying Accelerator Pedal Position (PWG)

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The ECM provides voltage (5v) and ground for the Hall sensors. As the accelerator pedal is moved from rest to full throttle, the sensors produce a variable voltage signal.

Hall sensor 1 (request) = 0.5 to 4.5 volts

Hall sensor 2 (plausibility) = 0.5 to 2.0 volts

If the signals are not plausible, the ECM will use the lower of the two signals as the request input. The throttle response will be slower and the maximum throttle response will be reduced.

Fig 4: Identifying Throttle Pedal Position (PWG)

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Electronic Throttle Actuator (EDR): The EDR is specifically designed for the S54 engine. This allows one actuator to operate all six throttles via a common linkage.

The ECM provides the operating voltage and ground to the EDR for opening and closing the throttles. The ECM monitors a feedback potentiometer located on the actuator shaft (arrow) for actuator position/plausibility (closed 4.5v - full open 0.5v).

There is a return spring fitted to the actuator lever end that assists in closing the throttles.

Fig 5: Identifying Electronic Throttle Actuator (EDR)

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Throttle Valve Position: A potentiometer is fitted to the end of the throttle shaft (arrow) that allows the ECM to monitor throttle position.

This signal is used by the ECM for a position/plausibility check (closed 0.5v - full open 4.5v).

Fig 6: Identifying Throttle Valve Position

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Idle Air Actuator: The Idle Air Actuator is a two-coil rotary actuator (ZWD5). The S54 features a second air supply system that functions independent of the throttle valve control system (EDR). This actuator regulates air by-passing the throttle valves to control low engine speed.

The valve is supplied with operating voltage from the ECM Relay. The ECM is equipped with two final stage transistors which will alternate positioning of the actuator.

The final stages are "pulsed" simultaneously by the ECM which provides ground paths for the actuator. The duty cycle of each circuit is varied to achieve the required idle RPM.

Fig 7: Identifying Idle Air Actuator

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The maximum air flow of the idle air actuator (80 kg/h) permits emergency operation of the vehicle (limp-home mode).

The valve (2) regulates air flow through an external air distribution pipe to the individual throttle housings. The inducted air is shared between the idle actuator and throttle valves depending on the engine load.

Fig 8: Identifying Valve

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Hot-Film Air Mass Meter (HFM): The air volume input signal is produced electronically by the HFM which uses a heated metal film in the air flow stream. The HFM is integral with the air filter upper housing (one-piece).

The ECM Relay provides the operating voltage. As air flows through the HFM, the film is cooled changing the resistance which affects current flow through the circuit. This also causes voltage drop across circuit as the resistance changes. The ECM monitors this change and regulates the amount of fuel injected.

Fig 9: Identifying Hot-Film Air Mass Meter (HFM)

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Air Temperature Signal: The HFM contains an integral air temperature sensor. This is a Negative Temperature Coefficient (NTC) type sensor. This signal is needed by the ECM to correct the air volume input for changes in the intake air temperature (air density) affecting the amount of fuel injected, ignition timing and Secondary Air Injection activation.

The ECM provides the power supply to this component. The sensor decreases in resistance as the temperature rises and vice versa. The ECM monitors an applied voltage to the sensor that will vary as air temperature changes the resistance value.

Suction Jet Pump: The ECM regulates the Suction Jet Pump (1) to provide sufficient vacuum for the brake booster under all operating conditions. The ECM controls the Suction Jet Pump Solenoid (2) to allow vacuum flow through.

Additional vacuum compensation is applied to the brake booster when the circuit is "deactivated" (solenoid sprung open).

Vacuum enhancement is limited to the brake booster when the control circuit is "activated" (solenoid powered closed).

Fig 10: Identifying Suction Jet Pump (1) And Solenoid (2)

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