(Injection Regulation, Function - GF07.10-P-1004OGR)

ENGINE 642.8 in MODEL 166 

up to model year 2016 

Function requirements for CDI injection regulation, general points 

• Circuit 87 (Engine management ON)
• Engine runs

CDI injection regulation, general 

The CDI control unit (N3/9) allocates the required fuel quantities to the engine.

The CDI control unit calculates the fuel quantity and the characteristic map-dependent injection period and fuel pressure in the rail on the basis of the following sensors and signals:

• Engine oil temperature sensor (B1)
• Left hot film mass air flow sensor (B2/6), for the intake air mass
• Left intake air temperature sensor (B2/6b1)
• Right hot film mass air flow sensor (B2/7), for the intake air mass
• Right intake air temperature sensor (B2/7b1)
• High pressure fuel pressure sensor (B4/6)
• Boost pressure sensor (B5/1)
• Camshaft Hall sensor (B6/1)
• Coolant temperature sensor (B11/4)
• Charge air temperature sensor (B17/8)
• Pressure sensor downstream of air filter (B28/5)
• Accelerator pedal sensor (B37), driver engine load request
• Accelerator pedal sensor, accelerator pedal operation fast or slow (when accelerating)
• Fuel temperature sensor (B50)
• Crankshaft Hall sensor (B70), engine rpm
• Oxygen sensor upstream of catalytic converter (G3/2)
• Temperature sensor upstream of diesel particulate filter (B19/9), for controlling the exhaust aftertreatment on vehicles with code (474) Particulate filter
• Temperature sensor upstream of ATL (B19/11)
• DPF differential pressure sensor (B28/8), for load condition of diesel particulate filter (DPF) on vehicles with code 474 (Particulate filter)
• DPF differential pressure sensor for OBD (B28/16), on vehicles with code U42 (BlueTEC (SCR) diesel exhaust treatment) and code 494 (USA version)
• Atmospheric pressure sensor in CDI control unit, atmospheric pressure for altitude adaptation

Function sequence for CDI injection regulation 

The injection regulation is described in the following steps:

• Function sequence for fuel pressure control 
• Function sequence for preinjection 
• Function sequence for main injection 
• Function sequence for post injection 
• Function sequence for injection quantity correction 

Function sequence for fuel pressure control 

The fuel pressure control is subdivided into the following control strategies:

• Pressure regulating valve (Y74) regulation 
• 2-control concept regulation 
• Quantity control valve (Y94) regulation 

Pressure regulating valve regulation 

The fuel pressure in the rail is controlled by the pressure regulating valve after each engine start. At this time the quantity control valve is de-energized and therefore fully open, meaning that the maximum fuel quantity is delivered to the fuel system high pressure pump.

Pressure regulating valve regulation takes place under the following conditions:

• Up to 5 s in idle after each manual engine start
• Up to a fuel temperature of 20°C

Pressure regulating valve regulation causes the cold fuel to be heated rapidly by the fuel being forced at high pressure through a narrow gap in the pressure regulating valve.

2-control concept regulation 

If the conditions for the pressure regulating valve control are no longer being met, the fuel pressure in the rail is regulated jointly by the pressure regulating valve and the quantity control valve at v ≤ 12 km/h or in deceleration mode at v > 12 km/h.

Quantity control valve regulation 

If the conditions for pressure regulating valve control and 2-controller-concept control are not being met, the fuel pressure in the rail is controlled by the quantity control valve.

The pressure regulating valve is closed in a controlled manner and thus performs a retention function.

The advantage of quantity control valve regulation is that the fuel system high pressure pump only needs to compact the fuel which the quantity control valve lets through to the fuel system high pressure pump as required by the current situation. This relieves the fuel high-pressure pump and reduces fuel consumption.

The fuel system high pressure circuit is unpressurized after switching off the engine.

For vehicles with code B03 (ECO start/stop function) a fuel pressure of about 250 bar is maintained in the fuel system high pressure circuit during the automatic engine stop.

Function sequence for preinjection 

The objective of preinjection is to reduce combustion noise and exhaust emissions. This is achieved by injecting fuel one or two times before the main injection starts to make the combustion run smoother. The start of actuation of the fuel injectors (Y76) for preinjection is calculated by the CDI control unit operating point dependent. In addition, the ambient condition and the engine temperature, the last beginning of actuation of the main injection and the on-board electrical system voltage determined by the on-board electrical system battery (G1) are taken into account.

The preinjection is suppressed by the CDI control unit if one of the following conditions exists:

• The preinjection time is exceeded
• The calculated preinjection quantity is too low
• The detected engine speed is too high
• The main injection quantity is too low
• Fuel pressure in rail too low
• The engine is switched off

Function sequence for main injection 

The main injection is performed immediately after preinjection and generates power and torque. Main injection is controlled by the start of actuation (injection timing point) and the actuation duration (injection period).

The main injection is suppressed by the CDI control unit if one of the following conditions exists:

• Fuel temperature limit exceeded
• Engine speed > 5000 rpm
• Fuel pressure in rail too low
• Engine is in the deceleration mode
• An external quantity intervention occurs, for example by the ESP®
• The engine is switched off

Function sequence for post injection 

Post injection serves to increase the exhaust temperature as well as to support conversion of the exhaust gas components in the diesel oxidation catalytic converter and to support DPF regeneration. For this purpose, the load condition of the diesel particulate filter (DPF) is recorded by the differential pressure sensor (DPF). The 2nd post injection further increases the exhaust temperature and the regeneration process is triggered. The soot particles in the exhaust gas are then burnt subsequently.

The post injection is suppressed by the CDI control unit if one of the following conditions exists:

• The preinjection time is exceeded
• The detected engine speed is too high
• The calculated quantity of post-injection is too small
• The main injection quantity is too low
• Fuel pressure in rail too low
• The engine is switched off

Additional function requirements 

Injection quantity correction 

• Engine speed between 1200 rpm and 3000 rpm (deceleration mode or normal driving mode)
• Engine oil temperature >80°C
• Fuel temperature 30 to 50°C

Function sequence for injection quantity correction 

Injection quantity correction is subdivided into 2 subareas:

• Zero quantity calibration 
• Quantity mean value adaptation 

Zero quantity calibration 

Due to friction and the associated wear during opening and closing of the fuel injectors a change in injection quantity takes place over the runtime. This change in injection quantity can be corrected by adapting the actuation duration (zero quantity calibration). This actuation duration corresponds to a defined injection quantity. The difference between the new and nominal actuation duration is used for injection quantity correction. Zero quantity calibration is conducted for various prescribed injection pressures in deceleration mode. The fuel injectors are actuated one after the other in this phase using a calibration value and the respective engine speed evaluated. If the respective engine speed deviates from the stored specified value then the calibration value is adapted and stored in the CDI control unit.

Quantity mean value adaptation 

Quantity mean value adaptation is a teach-in function of the CDI control unit which is used to adjust the exhaust gas recirculation rate (EGR rate), so that the emission levels do not deteriorate due to the tolerances of the fuel injectors, the left hot film MAF sensor and the right hot film MAF sensor.

To do this, the CDI control unit reads in the following signals:

• Left hot film mass air flow sensor
• Right hot film mass air flow sensor
• Oxygen sensor upstream of catalytic converter

The CDI control unit alters the AGR rate via the exhaust gas recirculation actuator (Y27/9) and the throttle valve actuator (M16/6). The residual oxygen content is monitored by the oxygen sensor upstream of catalytic converter.

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