Knock Control System

Knock Control System:

PURPOSE
Reduce "knocking" under various conditions associated with turbocharger operation, preventing engine damage.

LOCATION
Boost control solenoid valve: Bottom of turbocharger assembly
Knock sensor: Back side of engine block
Knock control unit: Center of firewall

OPERATION
Ignition timing is retarded by the Electronic Control Assembly (ECA) when knocking occurs. If knocking persists, and the engine is in a high-boost condition, maximum boost is also reduced by the [1][2]turbo boost control solenoid valve.

The actuator boost pressure line to the actuator is split, with one line going to the actuator and the other through the boost control solenoid valve to the inlet side (turbine housing) of the turbocharger.

The boost control solenoid valve receives its signal from the ECA. The ECA determines boost control solenoid valve position from signals it receives from the knock control unit. If a "no-knock" condition is detected by the ECA, the solenoid valve is fully open and boost pressure is divided between the two lines. Maximum boost is set at 8.7 psi (60 kPa).

If a "knocking" condition is detected under high-speed or full throttle acceleration and continues after ignition timing is retarded, the ECA signals the boost control solenoid valve to begin closing. The valve closes step by step to limit pressure vented to the turbocharger inlet side (turbine housing). This reduces boost pressure needed to open the wastegate, reducing maximum boost. This continues until the vent line is fully closed, if necessary, to limit boost even more. With the boost control solenoid valve fully closed, maximum available boost is 6.5 psi (45 kPa).