Boost Pressure Control

PRINCIPLE OF OPERATION, BOOST PRESSURE CONTROL





Boost Pressure Control--takes place by means of a 2-coil three-way solenoid valve which is connected by means of hoses to the turbo unit wastegate, compressor outlet and compressor inlet.

The solenoid valve is supplied with +54 current via fuse 24 and is controlled from pins 26 and 2 of the control module. The control voltage is a PWM signal which is 90 Hz below 2500 rpm and 70 Hz above 2500 rpm. The purpose of this change in frequency at 2500 rpm is to avoid the phenomenon of resonance in the air hoses.

The control module adjusts boost pressure by grounding pins 26 and 2 alternately. By grounding pin 2 for a, longer time than pin 26 the boost pressure is reduced. Conversely, grounding pin 26 for a longer time than pin 2 increases the boost pressure.

The control module determines boost pressure on the basis of throttle position and engine rpm. It obtains the current boost pressure from the manifold absolute pressure sensor. In 1st gear the boost pressure is reduced. The control module calculates the gear position by comparing the speed of the car with engine rpm.

If the control module has been de-energized, the engine will have to be revved up a number of times at wide open throttle in order to achieve correct boost pressure build-up.







If knocking occurs in spite of retarding the ignition and using a richer mixture, the boost pressure will also be reduced.

In the event of an open circuit in any of the leads connected to the solenoid valve, basic charging pressure will be obtained.

In the event of a break in any of the hoses or a fault in the solenoid valve, excessively high boost pressure may be obtained. The control module will then stop fuel injection at 0.65-1.35 bar, depending on the engine version.

Cars With Automatic Transmission--When the selector lever is moved to a position other than P or N, battery positive is applied to pin 14 of the control module and the control module is programmed for automatic transmission. Cars with automatic transmission have reduced boost pressure.

Brake Light Switch--When the brake pedal is depressed, battery positive is applied to pin 15 of the control module and maximum boost pressure will then be basic charging pressure.

Reverse Gear (not cars with automatic transmission)--When reverse gear is engaged, basic charging pressure will be obtained. This function is activated when battery positive, from the gear lever or reversing light switch, is applied to pin 13 of the control module.

Cruise Control (not cars with electronic throttle system [ETS])--On activation of the Cruise Control system, pin 36 of the control module is grounded and basic charging pressure is obtained.


Speed Limiting--Cars with a boost pressure control valve are limited to a maximum speed of 240 km/h through reduction of boost pressure.