Mixture Formation -- Basic Knowledge -- 251 Chassis: Adjustments Mercedes-Benz R-class W251 facelift

Self-adjustment of mixture formation, function - GF07.10-P-1029MIG

ENGINES 272.945 in MODEL 251.054/154 as of model year 2009/AEJ 08

ENGINES 272.967 in MODEL 164.186 as of model year 2009/AEJ 08 model refinement package

ENGINES 272.967 in MODEL 164.156

ENGINES 272.967 in MODEL 251.056/065/156/165 as of model year 2009/AEJ 08

ENGINES 273.923 in MODEL 164.871 as of model year 2009/AEJ 08

ENGINES 273.963 in MODEL 164.172 as of model year 2009/AEJ 08 model refinement package

ENGINES 273.963 in MODEL 164.886, 251.072/172 as of model year 2009/AEJ 08

Function requirements Self-adjustment for mixture formation, general points

1. Circuit 87M ON (engine control ON)
2. Engine running
3. Lambda regulation active
4. Engine at idle or on partial load

Self-adjustment for mixture formation, general points

For regulated catalytic converters the lambda control determines the injection time so exactly that a specified fuel-air ratio (lambda) is maintained under all operating conditions.

Self-adjustment for mixture formation, function sequence

Self-adjustment ensures that the mixture composition in the control mode (e.g. warming-up phase) is neither too rich nor too lean. It also prevents the lambda control from coming to the end stop at high altitudes.

The following errors can occur during mixture formation

1. Unmetered air
2. Wear or carbon deposits on fuel injection valves (Y62)
3. Faulty pressure sensor (B28) (intake manifold air pressure)
4. Transition resistance in the hot film mass air flow sensor (B2/5)
5. Defective purge control valve (Y58/1)
6. Harmful fuel pressure regulator
7. Wear to the engine (e.g. valve leakage)

If a fault occurs, the ME-SFI [ME] control unit (N3/10) automatically makes a correction in the mixture formation. In this case, the lambda performance map is shifted within the specified limits so that the lambda control is not at the upper or lower end stop.

Shifting of the lambda performance map

Scheme 127

If the mixture composition is constantly drifting out of the middle controlled range (e.g. 0 ± 18%), the ME-SFI [ME] control unit in certain operating conditions shifts the lambda performance map until the lambda control factor is about 0%.

This shifting of the lambda performance map is the self-adjustment of the mixture formation process to the existing air/fuel mixture.

Once this self-adaptation has taken place the lambda regulating factor will again find itself in the medium range.

Self-adjustment values shown with the Diagnosis Assistance System (DAS)

The following can be read out using the DAS

1. Shifting of the lambda performance map
2. Direction of shift (rich or lean)
3. Size of the shift

Presentation takes place in the form of a factor and means that the measured air mass value is multiplied by the factor.

Example

Measured air mass: 150.0 kg/hour

Indicated factor in the DAS: 1.1

To determine the injection duration (fuel injection quantity), the ME-SFI [ME] control unit uses a mathematical air mass value of 165 kg/h (150 kg/h X 1.1).

The maximum correction values are -0.68 to +1.32.

Self-adjustment of mixture formation, function - GF07.10-P-1029V

ENGINES 272.920 in MODEL 203 up to model year 2008/AEJ 07

ENGINES 272.922 in MODEL 211

ENGINES 272.940 in MODEL 203 up to model year 2008/AEJ 07

ENGINES 272.941 in MODEL 203 up to model year 2008/AEJ 07

ENGINES 272.942 in MODEL 171 up to model year 2008/AEJ 07

ENGINES 272.943 in MODEL 211, 219

ENGINES 272.944 in MODEL 211

ENGINES 272.945 in MODEL 251 up to model year 2008/AEJ 07

ENGINES 272.946 in MODEL 221 up to model year 2008/AEJ 07

ENGINES 272.960 in MODEL 203 up to model year 2008/AEJ 07

ENGINES 272.963 in MODEL 171 up to model year 2008/AEJ 07

ENGINES 272.964 in MODEL 211, 219

ENGINES 272.965 in MODEL 221 up to model year 2008/AEJ 07

ENGINES 272.966 in MODEL 230 up to model year 2008/AEJ 07

ENGINES 272.967 in MODEL 164, 251 up to model year 2008/AEJ 07

ENGINES 272.970 in MODEL 203 up to model year 2008/AEJ 07

ENGINES 272.972 in MODEL 211

ENGINES 272.975 in MODEL 221 up to model year 2008/AEJ 07

ENGINES 273.922 in MODEL 221 up to model year 2008/AEJ 07

ENGINES 273.923 in MODEL 164 up to model year 2008/AEJ 07

ENGINES 273.924 in MODEL 221 up to model year 2008/AEJ 07

ENGINES 273.960 in MODEL 211, 219

ENGINES 273.961 in MODEL 216, 221 up to model year 2008/AEJ 07

ENGINES 273.962 in MODEL 211

ENGINES 273.963 in MODEL 164, 251 up to model year 2008/AEJ 07

ENGINES 273.965 in MODEL 230 up to model year 2008/AEJ 07

ENGINES 273.967 in MODEL 209

ENGINES 273.968 in MODEL 221 up to model year 2008/AEJ 07

ENGINES 272.940 in MODEL 209

ENGINES 272.960 in MODEL 209

Scheme 128

On vehicles fitted with a closed-loop controlled catalytic converter, the lambda control determines the injection time so exactly that a certain fuel-air ratio (lambda) is maintained in all operating states.

If faults occur, the ME-SFI [ME] control unit automatically makes a correction in the mixture formation. Here the lambda performance map is shifted within certain limits in such a way that the lambda control is not at the upper or lower regulation limit (d).

The following faults require a mixture adjustment

1. Wear or carbon deposits on fuel injection valves
2. Fault on mass air flow sensor
3. Incorrect injection pressure (e.g. through blocked fuel filter)
4. Defective purge control valve
5. Engine wear (e.g. leaky valves)

If the mixture composition constantly drifts out of the middle control range (e.g. 0 ± 10%) the ME-SFI [ME] control unit under certain operating conditions shifts the lambda map sufficiently far until a lambda control factor of approx. 0% (g) is again achieved.

Self-adjustment ensures that the mixture composition in the control mode (e.g. warming-up phase) is neither too rich nor too lean. This also prevents the lambda control from moving up to the control limit at high altitudes.

Example

As the result of a lean fuel/air mixture the readout of the lambda control factor changes to 18% (e). Under certain operating conditions the lambda performance map is shifted (arrow) by the ME-SFI [ME] control unit.

This shifting of the lambda performance map is the self-adjustment of the mixture formation process to the existing air/fuel mixture. After this self-adjustment the lambda control factor is again in the central control range (g).

This self-adjustment of the mixture formation can be carried out in the following operating states

1. Idle speed
2. Lower part load
3. Upper partial load.

The following actual values can be read out using STAR DIAGNOSIS

1. Lambda map shift active
2. Direction of the shift (tendency towards rich or lean)
3. Extent of the shift

Representation of self-adjustment values with STAR DIAGNOSIS in idle

The representation in milliseconds means that the value displayed is added to, or subtracted from, the air mass inducted by the engine in order to determine the injection time.

The maximum correction value is ± 1 ms.

Example

Calculated injection time (performance map):3.0 ms

Displayed correction value:+0,3 ms

For determining the injection time (fuel injection quantity) the ME-SFI [ME] control unit uses a calculated value of 3.3 ms (3.0 ms+0.3 ms).

Representation of self-adjustment values with STAR DIAGNOSIS for partial load

The representation of the factor means that the indicated value for determining the injection time is multiplied by the air mass inducted by the engine.

The correction factor lies between 0.68 and 1.32.

Example

Calculated air mass:150 kg/hour

Displayed correction value:1,10

A calculated air mass value of the of 165 kg/h is used by the engine control unit to determine the injection time (fuel injection quantity).

Camshaft adjustment, function - GF07.61-P-4021MIG

ENGINES 272.945 in MODEL 251.054/154 as of model year 2009/CY 08

ENGINES 272.967 in MODEL 164.186 as of model year 2009/CY 08 model refinement package

ENGINES 272.967 in MODEL 251.056/065/156/165 as of model year 2009/CY 08

ENGINES 273.923 in MODEL 164.871 as of model year 2009/CY 08

ENGINES 273.963 in MODEL 164.172 as of model year 2009/CY 08 model refinement package

ENGINES 273.963 in MODEL 164.886, 251.072/172 as of model year 2009/CY 08

Function requirements of camshaft adjustment, general points

1. Circuit 87M ON (engine control ON)
2. Engine running

Camshaft adjustment, general points

The camshaft adjustment allows all four camshafts to be adjusted continuously by up to 40° CKA ( C ranK A ngle). This means the valve overlap in the event of a load change can be varied within wide limits.

This optimizes engine torque characteristics and improves the exhaust characteristics.

Valve overlap

The intake valves open before the exhaust valves close.

For camshaft adjustment, the ME-SFI (N3/10) control unit reads the following sensors

1. Hot film MAF sensor (B2/5), engine load
2. LH and RH intake camshaft Hall sensors (B6/4, B6/5), intake camshaft positions
3. LH and RH exhaust camshaft Hall sensors (B6/6, B6/7), exhaust camshaft positions
4. Coolant temperature sensor (B11/4)
5. Crankshaft Hall sensor (B70), engine speed

Camshaft adjustment function sequence

The function sequence is described in the following steps

1. Camshaft adjustment enable function sequence
2. Adjustment function sequence
3. Adjustment range function sequence
4. Start position function sequence
5. Valve overlap function sequence
6. Camshaft positions monitoring function sequence
7. Diagnosis function sequence

Camshaft adjustment enable function sequence

Camshaft adjustment is enabled by the ME-SFI [ME] control unit depending on engine speed and engine oil temperature.

The engine oil temperature is determined by the ME-SFI [ME] control unit using various operating data (e.g. coolant temperature, time, engine load) and a stored temperature model determined.

Engine oil temperature is important, even when the oil is hot, to ensure that there is sufficient oil pressure (>1.5 bar) for adjusting the camshafts

If the oil pressure is inadequate, first of all adjustment of the exhaust camshafts is not guaranteed, as these must be adjusted when the engine speed is dropping (low oil pressure) opposite to the direction of rotation of the engine.

A return spring is located in each exhaust-side vane-type adjuster for support.

If all four camshafts are adjusted, adjustment of the exhaust camshafts takes place after a delay (later). Oil supply problems are prevented and secure functioning of the locking mechanism achieved.

Release of the camshaft adjustment occurs dependent on load

1. For an 80°C engine oil temperature from about 600 RPM
2. For a 120°C engine oil temperature (inlet side) from about 800 RPM
3. For a 120°C engine oil temperature (exhaust side) from about 1050 RPM

Adjustment function sequence

The LH and RH intake camshaft solenoids (Y49/4, Y49/5) and the LH and RH exhaust camshaft solenoids (Y49/6, Y49/7) are actuated by the ME-SFI [ME] control unit with a PWM (pulse width modulated) signal.

The control plungers are adjusted via the performance map-dependent duty cycle. The oil quantities (pressure oil) for the vane-cell adjusters are controlled according to their position. The vane plungers in the vane-cell adjusters which are firmly connected to the camshafts are turned by the pressure oil.

Adjustment range function sequence

Intake camshafts:4° CKA before TDC ( T op D ead Center) to 36° CKA after TDC

Exhaust camshafts:20° CKA before TDC to 20° CKA after TDC

Start position function sequence

Intake camshafts: A 36° CKA after TDC

Exhaust camshafts:20° CKA before TDC

The camshafts are locked in a fixed position for starting by catch bolts (locked). This start position is unlocked hydraulically at the first actuation of the intake and exhaust camshaft solenoids.

Shown is oil flows in the intake camshaft vane-cell adjuster

Scheme 129

The upper half of the illustration shows

Filling oil galleries (A), oil galleries (B) open.

The lower half the illustration shows

Filling oil galleries (B), oil galleries (A) open.

Valve overlap function sequence

At low engine speed and load, the ME-SFI [ME] control unit sets a large valve overlap in order to produce internal exhaust gas recirculation. In this case less fresh air is suctioned in while exhaust gases which are still low in oxygen remain in the cylinders. This lowers the combustion temperature and reduces the formation of nitrogen oxides (NO X ).

The inducted air mass is reduced by the quantity of exhaust gases remaining. The ME-SFI [ME] control unit shortens the injection time accordingly.

The smallest valve overlap for gas exchange occurs if the exhaust camshaft is adjusted to the maximum BTDC (advanced) and the intake camshaft to the maximum after TDC (retarded).

The resulting increased fresh air content produces more engine torque and engine power.

Camshaft positions monitoring function sequence

The camshafts positions are detected by the intake camshaft Hall sensors and the exhaust camshaft Hall sensors, and sent to the ME-SFI [ME] control unit. Detection of the positions takes place through detection of the positions of pulse wheels which are located at the front on the camshafts.

Diagnosis function sequence

During diagnosis of the camshaft adjustment, the ME-SFI [ME] control unit checks whether the camshafts are in start position at engine start and whether the required adjustment has been reached after the engine has been running for a short time. Output stage errors (in the ME-SFI [ME] control unit) of the camshaft solenoids and camshaft Hall sensor faults are also detected.

Shown is intake camshaft adjustment

Scheme 130

Shown is the intake camshaft vane-cell adjuster

Scheme 131

Electrical function diagram for camshaft adjustment ME Model 164 PE07.61-P-2773-97MAA Model 251 PE07.61-P-2773-97RAA ME-SFI [ME] control unit, component description N3/10 Engine 272 GF07.61-P-6000MIG N3/10 Engine 273 GF07.61-P-6000MLG

Camshaft adjustment, function - GF07.61-P-4021V

ENGINE 272.920 in MODEL 203 up to Model Year 8

ENGINE 272.922 in MODEL 211

ENGINE 272.940 in MODEL 203 up to Model Year 8

ENGINE 272.941 in MODEL 203 up to Model Year 8

ENGINE 272.942 in MODEL 171 up to Model Year 8

ENGINE 272.943 in MODEL 211, 219

ENGINE 272.944 in MODEL 211

ENGINE 272.945 in MODEL 251 up to Model Year 8

ENGINE 272.946 in MODEL 221 up to Model Year 8

ENGINE 272.960 in MODEL 203 up to Model Year 8

ENGINE 272.963 in MODEL 171 up to Model Year 8

ENGINE 272.964 in MODEL 211, 219

ENGINE 272.965 in MODEL 221 up to Model Year 8

ENGINE 272.966 in MODEL 230 up to Model Year 8

ENGINE 272.967 in MODEL 164, 251 up to Model Year 8

ENGINE 272.970 in MODEL 203 up to Model Year 8

ENGINE 272.972 in MODEL 211

ENGINE 272.975 in MODEL 221 up to Model Year 8

ENGINE 273.922 in MODEL 221 up to Model Year 8

ENGINE 273.923 in MODEL 164 up to Model Year 8

ENGINE 273.924 in MODEL 221 up to Model Year 8

ENGINE 273.960 in MODEL 211, 219

ENGINE 273.961 in MODEL 216, 221 up to Model Year 8

ENGINE 273.962 in MODEL 211

ENGINE 273.963 in MODEL 164, 251 up to Model Year 8

ENGINE 273.965 in MODEL 230 up to Model Year 8

ENGINE 273.967 in MODEL 209

ENGINE 273.968 in MODEL 221 up to Model Year 8

ENGINE 272.940 in MODEL 209

ENGINE 272.960 in MODEL 209

Scheme 132

Shown on ENGINE 272

With camshaft adjustment, all the four camshafts can be adjusted progressively up to a crank angle of 40°. This means the valve overlap in the event of a load change can be varied within wide limits. In the event of valve overlap, the intake valves open even before the exhaust valve has fully closed.

Adjustment range of camshafts in ° crank angle

Intake camshaft 4° BTDC up to 36° ATDC

Exhaust camshaft 20° BTDC up to 20° ATDC.

Interlocked start position in ° crank angle

Intake camshaft 36° ATDC

Exhaust camshaft 20° BTDC.

At a lower engine speed and load, a large valve overlap is set to obtain an inner exhaust gas recirculation. In doing so, less fresh gases are drawn in, as some exhaust gas low in oxygen still remains in the cylinder. The combustion temperature drops and the formation of NO X is reduced. The inducted air mass is reduced by the quantity of exhaust gases which remain. In line with this, the ME control unit meters less fuel.

The smallest valve overlap in the event of a load change takes place when the exhaust camshafts are turned to the maximum "Early" and the intake camshafts are turned to the maximum "Late". The increased fresh gas proportion leads to a greater torque and performance.

Enabling of the camshaft adjustment is dependent on the engine speed and engine oil temperature, to ensure sufficient oil pressure, even when the engine oil is hot (oil pressure for adjustment at least around 1.5 bar). If oil pressure is inadequate, first of all, adjustment of the exhaust camshafts is not guaranteed, as these must be adjusted when the engine speed is dropping and thus at a lower oil pressure to the direction of rotation of the engine. A return spring is located in each exhaust-side vane-type adjuster for support.

The engine oil temperature is determined by the ME control unit using various operating data (e.g. load, coolant temperature, time) and a stored temperature model determined.

Enabling of the load-dependent and speed-dependent camshaft adjustment takes place

1. from around 600 RPM at 80°C engine oil temperature
2. from around 800 RPM at 120°C engine oil temperature (intake side)
3. from around 1050 RPM at 120°C engine oil temperature (exhaust side)

The solenoids upstream of the camshafts are actuated by the ME control unit on the ground side. The control plungers of the vane-type actuators are operated via the map-dependent duty cycle. Depending on their position, the oil volume in the vane-type adjusters is controlled.

Camshaft adjustment takes place gradually when all camshafts must be further adjusted simultaneously to prevent oil supply problems. In doing so, the intake camshaft adjustment is projected.

Each camshaft position is detected via a camshaft Hall sensor. These are located upstream of the camshaft adjusters and detect the window positions in the pulse wheels. During diagnosis, a check is performed to establish whether the camshafts are in the interlocked start position and whether following a short waiting time, the required adjustment has also been performed. In addition, output stage errors for the solenoids and defective camshaft Hall sensors are detected.

Location of control valve, intake valve illustrated

Scheme 133

Oil flows in vane-type adjuster, intake side illustrated

Scheme 134

The upper half of the illustration shows: filling oil galleries A, oil galleries B open.

The lower half the illustration shows: filling oil galleries B, oil galleries A open.

Vane-type adjuster design, intake side illustrated

Scheme 135