944 Turbo

Optimal use of turbocharging cannot be reached with the old method of charging air pressure regulation by using a charging air pressure control valve (by-pass valve), which used the charging air pressure of the turbocharger as a regulator for air quantity.

The charging air pressure control valve must open at relatively low engine speed and in partial load range, in order to carry off the hot exhaust gas that is unused. On 944 Turbo models, the engine can now be operated with higher charging air pressure especially in a partial load range.

An electro-pneumatic cycling valve (solenoid), which receives signals from the control unit. These signals operate between the knock and charging air pressure control unit and charging air pressure control valve.

If the charging air pressure leaves the nominal curve and reaches or exceeds the safety limits for more than 3 seconds because of damage on the charging air pressure control valve or in the knock and charging air pressure regulating system, the injection signal is switched off immediately. The injection of gasoline is stopped. Injection starts up again only after the sensor plate in the airflow sensor has gone back to about 3/4 of the full deflection travel by way of the engine speed and/or accelerator pedal position. Full acceleration and driving is then possible after about one minute.