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RPM Control, Function - GF07.10-P-1008MNG

ENGINE 276.8 in MODEL 292 

ENGINE 276.8/9 in MODEL 166 

as of model year 2016 

Function requirements for rpm control, general points 

Rpm control, general 

Rpm control stabilizes the idle speed and limits the motor speed to protect the engine, the drivetrain and the vehicle. The ME-SFI [ME] control unit (N3/10) detects the engine speed via the crankshaft Hall sensor (B70) signal. For rpm limitation, the ME-SFI [ME] control unit reads in the following signals:

The ME-SFI [ME] control unit limits the engine speed by the following measures:

Function sequence for rpm control 

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

Function sequence for torque converter protection 

To protect the torque converter in selector lever positions "P" or "N" (no power flow) from excessive static internal pressure, the maximum engine speed is limited to approx. 4200 rpm. The ME-SFI [ME] control unit receives information about the current selector lever position from the fully integrated transmission control unit via the drive train CAN.

Function sequence for rpm limitation 

In order to protect the engine from inadmissible engine speeds during driving mode, the maximum engine speed is limited to about 6800 rpm. The ME-SFI [ME] control unit detects the driving mode on the "wheel speed" CAN signal, which is sent from the Electronic Stability Program control unit via the chassis CAN 1.

Function sequence for maximum speed limit 

When v = 250 km/h is reached, the ME-SFI [ME] control unit reduces the opening angle of the throttle valve and the injection period for the fuel injectors. These measures ensure simple maximum speed limit through the reduction of the engine torque.

Function sequence for throttle valve actuator defective 

In the event of a defective throttle valve actuator, the maximum engine speed is limited in idle to approx. 1400 rpm and in driving mode to approx. 1800 rpm.

Function sequence for idle speed control 

The idle speed control regulates and stabilizes the idle speed depending on operating conditions and engine loads when the accelerator pedal is not actuated.

For idle speed control the ME-SFI [ME] control unit also reads in the following signals:

The ME-SFI [ME] control unit controls the idle speed via the throttle valve actuator and adapts the injection period of the fuel injectors in accordance with the modified air mass. To assist with idle speed control, the ME-SFI [ME] control unit can adjust the ignition angle of the ignition coils as far as 36° CKA (C  rank A  ngle) toward "retarded" or 20° CKA toward "advanced".

IMPORTANT The ignition angle initiates a faster response through the ignition angle setting than the throttle valve adjustment.

The ME-SFI [ME] control unit regulates the idle speed in the following operating conditions and engine load conditions:

Warming-up phase 

In the warm-up phase, the ME-SFI [ME] control unit controls the idle speed dependent on the coolant temperature, in order to bring the catalytic converters more quickly up to operating temperature after engine start.

Additional function requirements in the warm-up phase are:

The ME-SFI [ME] control unit raises the idle speed to about 1100 to 1300 rpm for about 20 s.

After this time has elapsed, the idle speed is increased at a coolant temperature of <70°C for about 50 s by the ME-SFI [ME] control unit by about 50 to 100 rpm.

Engagement of gear range "D" or "R" 

When gear range "D" or "R" is selected, the idle speed is set to a lower value to reduce the tendency of the vehicle to creep forward. To do this, the ME-MFI [ME] control unit evaluates the "gear range engaged" CAN signal from the fully integrated transmission control unit.

Switch-in of the A/C 

When the engine is at idle, so that engine speed will not fall when the refrigerant compressor is engaged, the automatic air conditioning control and operating unit sends a status signal to the ME-SFI [ME] control unit before the AAC is engaged.

The ME-SFI [ME] control unit adapts the idle speed appropriately.

Undervoltage of the on-board electrical system battery 

If the ME-SFI [ME] control unit detects an undervoltage through "circuit 30", the idle speed is raised by about 100 rpm when gear range "D" or "R" is engaged, until the ignition is switched off.

Purge control 

The idle speed control prevents any change in the engine speed due to purging.

IMPORTANT Diagnosis

The basic setting of the idle speed can be read out and influenced using the Xentry Diagnostics.

  Electrical function schematic for rpm control   PE07.10-P-2708-97NBG
  Overview of system components for gasoline injection and ignition system with direct injection ENGINE 276.8 in MODEL 166 (except 166.063)
as of model year 2016		 GF07.70-P-9998MMX
    ENGINE 276.9 in MODEL 166
as of model year 2016		 GF07.70-P-9998MNG
    ENGINE 276.8 in MODEL 166.063
as of model year 2016		 GF07.70-P-9998MMM
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