Boost control (models equipped with a turbocharger)
When the volume of exhaust gases increases, the turbocharger starts to work faster, and at high engine speeds, there is a danger of excessive acceleration of the turbocharger, which can lead to engine damage. This problem is eliminated by the turbocharger bypass valve (WCS).
The hose connects the turbocharger to the valve diaphragm. When the pressure rises to a certain level, the compressed air acts on the valve diaphragm, which opens to mechanically actuate a damper inside the exhaust pipe. Part of the exhaust gases enter through the flap and bypass the turbocharger so that its speed slows down and the boost pressure decreases.
This is the easiest way to protect the turbocharger from high pressure. However, the ECM uses a control system that controls turbocharger boost to improve power output under acceleration and at various engine speeds.
Turbocharger bypass valve (WCS) (see illustration 11.35) located in the hose connecting the turbocharger to the valve. When the turbocharger bypass valve is open or partially open, the variable air volume (depending on the position of the turbocharger bypass valve) goes back, reducing the pressure in the system.
11.35 Turbocharger bypass valve (WCS)
Voltage is supplied to the turbocharger bypass valve or from the main or fuel pump relay (depending on the model), and ground for the valve is through a connection to pin #6 of the ECM.
When the engine is turned off, the turbocharger wastegate valve is closed and air is fully directed to the turbocharger wastegate actuator. This position provides safety when the WCS valve fails, the boost pressure will never reach its set limit and the engine power will not be reduced. When the engine is running, the electronic control unit pulses to open the wastegate so that approximately 50% of the air supplied by the turbocharger is directed directly to the valve. The electronic control unit sends pulses to the valve at a fixed frequency, and the duration of the pulse is changed so that the valve opens for longer or shorter periods of time, as needed. This method allows the ECU to adjust the exact opening time to achieve the correct boost pressure under all operating conditions. If the engine speed is below 6000 rpm, then the boost pressure is maintained within 0.9 bar. At 6000 and 6700 rpm, the turbocharger wastegate valve gradually closes, allowing more boost pressure to act on the valve. At 6700 rpm, the turbocharger bypass valve closes completely and all boost pressure is directed to the valve. Boost pressure is now maintained within 0.3 bar.
If the inlet air gets too hot (exceeds 70°С), then the air density decreases and the air-fuel mixture becomes poorer. A lean mixture can lead to detonation, which in turn can cause engine damage. When the air is overheated, the ECM responds to this condition by sending pulses to close the turbocharger wastegate to relieve the boost pressure. Lower boost pressure will lower the air temperature and knocking will be prevented.
Turbocharger Bypass Valve Voltage Values (WCS)
Terminal numbers
| WCS | Component | Element | Volts |
| 2 | Main relay: t6 | Nutrition | nbv |
| 1 | ECM: t6 | Switch wire | nbv |
See illustration 11.5
Turbocharger Wastegate Resistance Values (WCS)
Influence of external factors
- Intake manifold absolute pressure sensor (IDA)
- Badly adjusted or faulty turbocharger bypass valve
- Malfunction of the electronic control unit
Checking the turbocharger bypass valve (WCS)
1. Inspect the turbocharger wastegate multi-pin connector for signs of corrosion or damage.
2. Check that the connector terminal pins are properly installed and making good contact with the turbocharger wastegate multi-pin connector.
Checking the control signal of the turbocharger bypass valve
1. It is very difficult to check the control signal without mounting the car on the stand, since the signal is only at engine speeds of more than 2500 rpm and under load.
2. You can check the turbocharger wastegate waveform by connecting a portable oscilloscope to the turbocharger wastegate multi-pin connector terminals.
3. However, by performing the following test procedures, you can check the operation of the turbocharger bypass valve and its circuit.
Checking the operation of the turbocharger bypass valve
1. Connect the positive lead of the voltmeter (see note 2) to the turbocharger bypass valve multi-pin connector or connect an output block (WWII) between the multi-pin connector of the electronic control unit and the electronic control unit.
2. Connect the negative lead of an oscilloscope or voltmeter to ground on the motor.
3. Connect the positive probe of an oscilloscope or voltmeter to the wire attached to the power terminal No. 2 of the turbocharger bypass valve.
4. Turn on the ignition, check for nominal battery voltage at the supply terminal of the turbocharger bypass valve.
5. If there is no voltage, trace the wiring back to the main fuel injection relay.
6. Check the resistance of the turbocharger bypass valve.
7. Disconnect the turbocharger bypass valve multi-pin connector.
8. Turn off the ignition.
9. Disconnect electric sockets and vacuum tubes from the valve.
10. Check that air is not flowing from port A to port B, and that air is not flowing from port A to port C.
11. Connect the jumper wire from terminal #2 to power.
12. Connect the jumper wire from terminal #1 to ground.
13. Verify that air is now flowing from port A to port B, but no air is flowing from port A to port C.
14. If the turbocharger bypass valve fires, check the continuity of the electrical wiring between the turbocharger bypass valve and the ECM connection terminal.
15. If the turbocharger bypass valve wiring is in order, check all power and ground contacts of the electronic control unit. If these contacts are in working condition, then the electronic control unit may be faulty.
Turbocharger wastegate resistance
- Disconnect the multi-pin connector and check for voltage at the two terminals of the turbocharger bypass valve