Engine management system - EDC (Boost control): Description and operation

Boost control

Boost control is achieved by a wastegate actuator operating a mechanical flap, known as a wastegate, situated in the turbocharger. When operated, the wastegate allows exhaust gases to bypass the turbine side of the turbocharger, so decreasing the rotational speed of the turbine thereby reducing the pressure of the intake air.

The wastegate actuator consists of a diaphragm connected to a mechanical linkage which is opposed by an internal spring. Pressure from the compressor side of the turbocharger is applied to the actuator via a sensing pipe. The pressure acting on the actuator diaphragm builds up until it exceeds the opposing force of the internal spring (approx. 17 psi or 1.2 Bar) causing the mechanical linkage to move, thereby opening the wastegate on the turbocharger and so reducing the boost pressure. As boost pressure is reduced the mechanical linkage will move the other way closing the wastegate allowing the pressure to increase again. With the engine under significant load the wastegate actuator will be constantly opening and closing the wastegate.

Air cleaner

The air cleaner housing is located on the left hand side of the engine bay. The air cleaner housing is plastic moulded with a removable lid which is retained with spring clips. Removal of the lid allows access to the corrugated paper filter element.

An air intake pipe is located at the front of the air cleaner housing and draws air from within the engine compartment. A rubber hose is connected to the intake pipe and connects to a resonator box located in the front left hand wheel arch. The resonator box is used to reduce induction noise.

The outlet from the air cleaner housing has a plastic pipe which provides the location for the mass air flow sensor. The outlet pipe is sealed to the housing with an O-ring seal. A gauze filter in the pipe provides additional contamination protection.

A rubber hose connects the outlet pipe to the turbocharger. The rubber hose also connects a breather from the camcover to the air intake system. A plastic tube connected to the rubber hose provides additional reduction of induction noise.