Special tool
 | Boost pressure gauge 310 - 020 (23 - 021) |
 | Hand Vacuum/Pressure Pump 416 - D001 (23 - 036A) |
Operating principle - Cars with a diesel engine of 75 hp or 90 hp.
The turbocharger is controlled by a turbine bypass valve. The turbine bypass valve bypasses part of the exhaust gases behind the turbine and therefore acts as a regulator. The turbine bypass valve is pre-set when the car is assembled and is not subject to subsequent adjustment.
Operating principle - Cars with 115 hp diesel engine.
The turbocharger is designed to improve the engine's power supply and its dynamic characteristics. The following list details the problems related to the operation of the turbocharger.
- High engine speed results in increased turbine speed, and therefore the turbocharger creates excessive boost pressure.
- Low engine speed results in insufficient turbine speed, and therefore the turbocharger does not create sufficient boost pressure.
A variable turbocharger does not have a turbine bypass valve. Instead, it has variable vanes that are located in the turbocharger turbine housing. The turbocharger vanes act as a control element for the turbocharger boost pressure.
A variable turbocharger creates full boost pressure across the entire engine speed range, not just at high speeds. This is achieved by adjusting the position of the vanes and thereby changing the exhaust gas flow.
The exhaust gas flow velocity is increased independently of engine speed by changing the cross-section of the intake duct ahead of the turbocharger turbine. This allows the turbocharger turbine to spin faster. The higher turbocharger speed creates high turbocharger boost pressure at all engine speeds.
The turbocharger vanes are controlled by the Powertrain Control Module (PCM). REFER to WDS to perform turbocharger vane diagnostics.
Adjustment at low engine speed
| Pos. | Spare Part No | Name |
| 1 | - | Solenoid valve for adjusting the position of the blades |
| 2 | - | Atmospheric pressure |
| 3 | - | Vacuum |
| 4 | - | Adjusting ring |
| 5 | - | Blades |
| 6 | - | Blades |
| 7 | - | Turbine |
| 8 | - | Turbine |
| 9 | - | Vacuum diaphragm unit |
| 10 | - | RSM |
At low engine speeds, the PCM activates the vane position control solenoid valve to provide access for vacuum. The vacuum diaphragm unit moves the adjusting ring so that the vanes are set at a small sliding angle. The small inlet cross-section created for exhaust gas flow allows turbocharger boost pressure to build up quickly and easily at low engine speeds.
Adjustment at medium engine speed
| Pos. | Spare Part No | Name |
| 1 | - | Solenoid valve for adjusting the position of the blades |
| 2 | - | Atmospheric pressure |
| 3 | - | Vacuum |
| 4 | - | Adjusting ring |
| 5 | - | Blades |
| 6 | - | Blades |
| 7 | - | Turbine |
| 8 | - | Turbine |
| 9 | - | Vacuum diaphragm unit |
| 10 | - | PCM |
Adjustment at maximum engine speed
| Pos. | Spare Part No | Name |
| 1 | - | Solenoid valve for adjusting the position of the blades |
| 2 | - | Atmospheric pressure |
| 3 | - | Vacuum |
| 4 | - | Adjusting ring |
| 5 | - | Blades |
| 6 | - | Blades |
| 7 | - | Turbine |
| 8 | - | Turbine |
| 9 | - | Vacuum diaphragm unit |
| 10 | - | PCM |
As the engine speed increases, the cross-sectional area of the intake duct upstream of the turbocharger turbine increases continuously. The turbine speed and therefore the amount of air supplied to the engine is adjusted to match the engine speed. This means that the turbocharger boost pressure remains optimized over the entire engine speed range.
The maximum position of the turbocharger blades (maximum cross-sectional area in the open position) is also an emergency position, for example in the event of an electrical problem or a leak in the vacuum system. Therefore, there is a small chance of engine damage due to increased boost in the event of a problem in the turbocharger control.
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