ME-SFI starting, function

P07.61-3063-09

Shown on engine 272 in model 171

B2/5 Hot film mass air flow sensor

B6/4 Left intake camshaft Hall sensor

B6/5 Right intake camshaft Hall sensor

B6/6 Left exhaust camshaft Hall sensor

B6/7 Right exhaust camshaft Hall sensor

B11/4 Coolant temperature sensor

N73 EIS [EZS] control unit

S40/5 Start enable clutch pedal switch
(for manual transmission 716.6 )

T1/1...

T1/6 Ignition coil cylinders 1 to 6

Y3/8n4 Fully integrated transmission control (VGS) control unit

Y62 Fuel injection valves

CAN Data bus

B28 Pressure sensor (intake manifold pressure)

B70 Crankshaft Hall sensor

M1 Starter

M3 Fuel pump

M16/6 Throttle valve actuator

N3/10 ME-SFI [ME] control unit

N10/1kR Circuit 87 relay, engine

N10/1kS Starter relay

N10/2kA Fuel pump relay

N47-5 ESP and BAS control unit

Battery voltage

The fuel injection quantity is determined by the opening time of the fuel injection valves. This opening time is dependent on the battery voltage. The ME-SFI [ME] control unit extends the injection time in order to compensate the quantity injected if, for example, the battery voltage is low. No further engine start is possible below approx. 7 V.

Start quantity control

In order to facilitate starting of the engine when cold, additional fuel must be injected during engine start operation (depending on the coolant temperature). The increased fuel injection quantity is achieved by extending the injection time.

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Starter control

The solenoid switch of the starter (circuit 50) is actuated through the starter relay by the ME-SFI [ME] control unit.

With an automatic transmission, the engine can only be started in selector lever position "P/N" and when the service brake is operated. The P/N selector lever position information is sent via the CAN from the transmission control unit. The information "service brake operated " comes via CAN from ESP control unit.

 with manual transmission 716.6

According to legal requirements, the start enable clutch pedal switch is located on the underside of the clutch pedal. This switch ensures that the engine can only be started when the clutch pedal is fully depressed.

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Ignition

When the engine is started up to approx. 500 rpm, the ignition timing point is controlled based on the signals supplied by the camshaft Hall sensor. It is only when an engine speed of about 600 rpm is reached that the system switches over to a performance map dependent firing point.

Synchronizing of fuel injection and firing order

In order to achieve correct synchronization of the fuel injection and firing order for the respective cylinder, the order is synchronized during the first revolutions of the engine. The ME-SFI control unit requires the signals from the camshaft Hall sensor and crankshaft Hall sensor for this purpose.

Post-start enrichment

After the engine is started from cold, enrichment with additional fuel is necessary for a short time. The fuel which precipitates on the cylinder walls is compensated for by this enrichment, and the engine runs smoothly.

Enrichment of fuel in engine oil

For a cold start, fuel condensing on the still cold cylinder liner can enrich the fuel in the engine oil. Once the engine oil becomes hot, the fuel evaporates the fuel again and this is led again via the crankcase ventilation system to the engine for combustion. The mixture deviation (a rich mixture) in neutral can be up to

30% and is corrected by the lambda control. Mixture adaptation saves this correction as a long-term effect. This means that a subsequent start could fail if the start mixture is too lean, although no exhalation of fuel takes place. To prevent this, the ME-SFI [ME] control unit constantly calculates the fuel quantity in the engine oil. To do this, the number of starts, the start temperature and the subsequent operating duration are evaluated.