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Rpm Control, Function - GF07.10-D-1008HD

ENGINES 651.955/956/957 in MODEL 906 

with CODE (XZ1) Model generation 1 

with CODE (MZ0) Blue EFFICIENCY 

Function requirements 

General 

Rpm control stabilizes the idle speed and limits the motor speed to protect the engine, the drive train and the vehicle. The CDI control unit (N3/28) reads in the following sensors and signals for RPM limitation:

The CDI control unit limits the engine speed by the following measures:

Function sequence 

Regulation of the engine speed is described in the following steps:

Function sequence for torque converter protection (for transmission 722.6) 

To protect the torque converter in selector lever positions "P" or "N" (no power transmission) from excessive static internal pressure, the engine speed is limited to approx. 4200 RPM. The CDI control unit receives information about the current selector lever position from the ETC control unit via CAN C.

Function sequence for driving mode 

In order to protect the engine from inadmissible engine speeds during driving mode, the maximum engine speed is limited to about 4500 RPM.

The CDI control unit detects the driving mode on the "vehicle speed" CAN C, which is sent by the ESP control unit via CAN C.

Function sequence for idle speed control 

The idle speed control regulates and stabilizes the idle speed dependent on the operating conditions and engine loads, if the accelerator pedal module (B37/3) (for model 906) are not actuated.

For idle speed control the CDI control unit also reads in the following sensors and signals:

The CDI control unit subsequently regulates the fuel pressure in the rail via the quantity control valve and the pressure regulator valve and the injection time via actuations of the fuel injectors.

IMPORTANT The fuel pressure in the rail and injection timing of the following injectors gives the injection quantity.

The CDI control unit regulates the idle speed in the following operating and engine load conditions:

Actuation of the clutch pedal (for transmission 711.6) 

When actuating the clutch pedal the idle speed is stabilized. Clutch pedal actuation is detected by the CDI control unit over both clutch pedal switches.

Engagement of the selector lever position "D" or "R" (for transmission 722.6) 

When selector lever position "D" or "R" is selected, the idle speed is set to a lower value to reduce the tendency of the vehicle to creep. To do this the CDI control unit evaluates the signal "engaged selector lever position" from the ETC control unit via CAN C.

IMPORTANT For vehicles with transmission 722.6 the idle speed is 750 RPM and for vehicles with transmission 711.6 the idle speed is 810 RPM.

Switch-in of the A/C compressor () (with code (HH9) Regulated air conditioning, (Tempmatic)) 

So that the engine idle speed does not drop when the refrigerant compressor engages, the AAC [KLA] control and operating unit first sends a status signal to the CDI control unit.

The CDI control unit adapts the idle speed appropriately.

IMPORTANT The CDI control unit will interrupt refrigerant compressor cut-in under the following conditions:

Battery undervoltage 

If the CDI control unit detects an undervoltage through "circuit 30", the idle speed is raised by about 100 RPM when gear range "D" or "R" is selected, until the ignition is switched off.

IMPORTANT The basic setting of the idle speed can be read out and adjusted with the Diagnosis Assistance System (DAS).

Component description for CDI control unit N3/28 GF07.16-D-6000HD 
Component description for boost pressure sensor B5/6 GF07.04-D-6053HD 
- B5/9 Engine 651.955/957 GF07.04-D-6053HDA 
Component description for coolant temperature sensor B11/17 GF07.04-D-6040HD 
Component description for charge air temperature sensor B17/13 GF07.04-D-6050HD 
Component description for the crankshaft position sensor L5/10 GF07.04-D-6011HD 
Component description for pressure regulating valve Y74/5 GF07.05-D-6020HD 
Component description for fuel injectors Y76/14, Y76/15, Y76/16, Y76/17 GF07.03-D-6120HD 
Component description for quantity control valve Y94/3 GF07.05-D-6010HD 
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