Common rail diesel injection (CDI), function - GF07.16-P-0001GZ: Notes
ENGINE 642.940 in MODEL 164.120 /122 /822
ENGINE 642 in MODEL 463
The OM 642 is characterized and excels due to the following basic innovations:
- Common rail diesel injection (CDI)4
- V6 crankcase made out of aluminum instead of cast iron
- Balance shaft located in the "V" of both cylinder banks which turns in an opposite direction to the crankshaft
- Valve control with roller-type cam follower
- Load level controlled pre and post injection
- A flow dynamics optimized supercharging system consisting of a turbocharger with variable turbine geometry
- Exhaust gas recirculation (EGR) with water-cooled exhaust gas recirculation cooler
- Quick glow system with glow output stage (N14/3)
- Highly efficient ventilation system with centrifugal oil separator
The CDI 4 takes account of the following features of the extended demands upon a common rail injection system:
- Use of piezo injectors and thus more precise injections
- Hydraulically optimized 8-hole nozzle module
- Load-dependent, dual pre-injection to reduce combustion noise
- Load-dependent, double post-injection in vehicles with Code (474) Particulate filter
- Intake controlled high-pressure pump with lower than average operating energy input, leading to reduced fuel consumption
- A maximum injection pressure of 1600 bar
CDI controls the following functions via the CDI control unit (N3/9):
- Fuel supply in all operating conditions
- Controlling the glow functions
- Injection quantity control
- Emission control
- Boost pressure control
- Shutting of the refrigerant compressor (A9)
- Shut-off control
To do this, the CDI control unit reads in information from the following sensors:
- Oil temperature sensor (B1)
- Left hot film mass air flow sensor (B2/6)
- Intake air temperature sensor (B2/6b1)
- Right hot film mass air flow sensor (B2/7)
- Intake air temperature sensor (B2/7b1)
- Rail pressure sensor (B4/6B4)
- Charge pressure sensor (B5/1B5)
- Camshaft Hall sensor (B6/1)
- Coolant temperature sensor (B11/4B11)
- Charge air temperature sensor (B17/8)
- TWC [KAT] temperature sensor (B19)
- Temperature sensor upstream diesel particulate filter (B19/9) on models with code (474) particulate filter
- Pressure sensor downstream of air filter (B28/5B28)
- Differential pressure sensor (DPF) (B28/8) on models with code (474) particulate filter
- Accelerator pedal sensor (B37B37)
- Fuel temperature sensor (B50B50)
- Crankshaft Hall sensor (B70)
- Fuel filter water level sensor (B76) on vehicles with Code (494) USA version
- O2 sensor upstream of TWC (G3/2)
- Oil level indicator switch (S43)
The CDI control unit actuates the following actuators:
- Starter relay (F58kI)
- Fuel pump relay (F4kO)
- Throttle valve actuator (M16/6)
- Intake port shutoff motor(M55)
- Vent line heater element (R39/1R39)
- Left exhaust gas recirculation positioner (Y27/9)
- Pressure regulator valve (Y74)
- Cylinder 1 fuel injector (Y76y1)
- Cylinder 2 fuel injector (Y76y2)
- Cylinder 3 fuel injector (Y76y3)
- Cylinder 4 fuel injector (Y76y4)
- Fuel injector cylinder 5 (Y76y5)
- Fuel injector cylinder 6 (Y76y6)
- Charge pressure positioner (Y77/1)
- Quantity control valve (Y94Y94)
The CDI control unit communicates with the following components via the Local Interconnect Network (LIN):
- Alternator (G2)
- Glow time output stage
The CDI control unit is connected to the following control units via the Control Area Network Bus Class C (engine compartment) (CAN-C):
- Instrument cluster (A1A1)
- ESP control unit (N47-5)
- EIS [EZS] control unit (N73N73)
- Steering column module (N80N80)
- Central gateway control unit (N93N93)
- Fully integrated transmission control (VGS) control unit (Y3/8n4)
STAR DIAGNOSIS can be used to read out system errors that occur, which are stored in the fault memory of the CDI control unit. This also applies for system faults which occur in the glow system, which were recognized by the glow time output stage and transmitted via the drive LIN to the CDI control unit.
Fuel supply
The CD is supplied with fuel by the fuel pump (M3). For this purpose, the CDI control unit actuates the fuel pump via the fuel pump relay, which delivers the fuel via the fuel main filter to the common rail high pressure pump. According to actuation by the CDI control unit, the quantity control valve regulates the feed to the common rail high pressure pump. Any fuel not required flows back into the fuel tank via the return line.
Control of the glow system at engine start and during driving mode
CDI actuates the glow time output stage via the CDI control unit. This then actuates the (R9) glow plugs. The following glow types exist:
- Preglowing
- Start-readiness glowing
- Start-glowing
- Afterglowing
- Diagnosis glowing
Injection quantity control at engine start and during driving mode
The CDI controls the fuel injectors (Y76) via the CDI control unit depending on speed and load. A distinction is made between "preinjection", "main injection" and "post-injection".
Emission control system
The emissions output by the engine are cleaned in the exhaust system by a near-engine mounted catalytic convertor (TWC). The catalytic convertor also serves to reduce noise pollution. A lambda control is also used. On vehicles with Code (474) Particulate filter, a diesel particulate filter (DPF) is used.
Charge pressure control
The CDI actuates the boost pressure positioner via the CDI control unit by means of a pulse width modulation (PWM) signal. The boost pressure positioner adjusts the position of the guide vanes in the turbocharger via a linkage. In this way the boost pressure is controlled. Thus a high boost pressure is possible even at low RPM.
Refrigerant compressor shut-off
Function prerequisites:
- AC system activated
- Engine speed <2000 RPM
- The values of the accelerator pedal sensor is > 95 %
The CDI control unit interrupts actuation of the refrigerant compressor. If the above listed function requirements are no longer met, the CDI control unit re-actuates the refrigerant compressor.
Shutoff control
The function requirement for shutoff control "Circuit 15 OFF". Via the CDI control unit, CDI actuates the quantity control valve and the pressure regulator valve. The quantity control valve interrupts the supply to the common rail high pressure pump and the pressure regulator valve opens the connection to the return line.
| Common rail diesel injection (CDI), location of components | Vehicle side | GF07.16-P-0001-01GZF | |
| Engine side | GF07.16-P-0001-01PM | ||
| Common rail diesel injection (CDI) function diagram | Except Code (474) Particulate Filter | GF07.16-P-0001-03GZ | |
| With Code (474) Particulate filter | GF07.16-P-0001-03GZX | ||
| Common rail diesel injection (CDI), model and major assembly overviews | GF07.16-P-0001-05P | ||
| Common rail diesel injection (CDI), control unit input signals | GF07.16-P-0001-06GZ | ||
| Common rail diesel injection (CDI), control unit output signals | GF07.16-P-0001-07GZ | ||
| CDI ignition ON, function | GF07.16-P-2000GZ | ||
| CDI starting, function | GF07.16-P-2001GZ | ||
| CDI idle speed, function | GF07.16-P-2002P | ||
| CDI driving mode, function | GF07.16-P-2003GZ | ||
| European On-Board Diagnosis (EOBD) CDI function | Except Code (494) USA version | GF07.16-P-3200GZ | |
| On-board Diagnosis (OBD) CDI function | With Code (494) USA version | GF07.16-P-3201GZ |