Boost pressure control
The boost pressure sensor is located in the intake tract behind the throttle pipe. The sensor sends to the ECM (the engine control unit) voltage signal corresponding to the pressure in the intake manifold. The BP sensor has a 3-pin connector that is connected to the eCm (the engine control unit). Through it, a reference signal of 5 V is supplied from eCm (the engine control unit), signal for ECM (the engine control unit) and the sensor is connected to ground.
A diaphragm-type sensor is used to measure boost pressure. ECM (the engine control unit) uses the BP sensor signal for the following functions:
- Maintaining boost pressure in the intake manifold.
- Reducing exhaust smoke when driving at high altitudes.
- EGR system management (exhaust gas recirculation systems) .
- Management of the block of vacuum regulation.
If the BP sensor is faulty, the ECM (the engine control unit) uses the default pressure value of 1013 mbar. The failure of the boost pressure sensor may be accompanied by the following symptoms:
- Altitude corrector not working (black smoke from the exhaust)
- Boost pressure control not working
The boost pressure is controlled by a gearless electric drive. The electric drive is located in the side part of the turbocharger and is connected by rods with the guide vanes. It uses a servo motor and has a built-in controller.
The electric drive can turn the blades at an angle of 60 degrees and memorize the extreme positions. The drive is controlled by PWM signals (pulse width modulation) , transmitted by the ECM (the engine control unit) . For more information refer to Turbocharger (303-04D Fuel Charging and Controls - Turbocharger - 2.7L Diesel)
Rail pressure control valve (PCV)
Item name | Spare part number | Description |
1 | - | Fuel control valve |
2 | - | High pressure fuel pump |
3 | - | Fuel rail pressure regulator |
The fuel rail pressure regulator is built into the high pressure fuel pump. It regulates the fuel pressure in the fuel rail and is controlled by the ECM (the engine control unit) . The regulator is a solenoid valve with PWM (pulse width modulation) -management.
When the solenoid is powered off, an internal spring closes the valve. When the fuel pressure equals or exceeds 100 bar, the spring force will be overcome and the overpressure fuel will be bled into the return line. When the pressure drops to about 100 bar or less, the spring force will overcome the fuel pressure and close the valve. When the ECM (the engine control unit) activates the solenoid valve, the valve closes, allowing fuel pressure to rise. The pressure in the fuel rail in this condition can reach approximately 1300 bar.
ECM (the engine control unit) regulates the fuel pressure in the fuel rail by controlling the solenoid valve with PWM (pulse width modulation) -signal. By changing the PWM duty cycle (pulse width modulation) -signal, ECM (the engine control unit) can precisely regulate the fuel pressure in the fuel rail supplied to the injectors according to the engine load. This is achieved by changing the capacity of the valve, which regulates the pressure in the high pressure circuit, changing the amount of fuel bled from the rail into the backflow line.
Fuel rail pressure regulator receives PWM (pulse width modulation) -signal from ECM (the engine control unit) , varying in the range of 0-12 V. ECM (the engine control unit) controls the operation of the regulator, using the following information to determine the required fuel pressure:
- Fuel pressure in the fuel rail
- Engine load
- Accelerator pedal position
- Coolant temperature
- Engine crankshaft speed
If the fuel pressure regulator fails completely, the engine will not start.
In the event of a partial failure of the ECM fuel rail pressure regulator (the engine control unit) actuates the solenoid valve by means of a minimum duty cycle signal, as a result of which the injection volume is limited.
Fuel control valve
The fuel control valve is built into the high pressure fuel pump. VCV valve bleeds excess fuel back to the fuel tank (or to the low pressure circuit), or directs to PCV. Bleeding excess fuel avoids the power consumption of the high pressure pump for unnecessary compression of the fuel in the rail and the concomitant heating of the fuel.
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