ME-SFI starting, function

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.

Battery voltage and voltage supply

The injected fuel quantity is determined by the injection duration of the injection valve (fuel injection valve for cylinder 1 (Y62/1), fuel injection valve for cylinder 2 (Y62/2), fuel injection valve for cylinder 3 (Y62/3), fuel injection valve for cylinder 4 (Y62/4), fuel injection valve for cylinder 5 (Y62/5) and fuel injection valve for cylinder 6 (Y62/6)).

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This opening time is dependent on the battery voltage. The ME-SFI control module (N3/23) 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.

Post-start enrichment

After the engine is started from cold, enrichment with additional fuel is necessary for a short time. Enrichment compensates for the fuel that precipitates on the cylinder walls and the engine runs smoothly.

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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. To do this the ME-SFI control module needs the signals from the rpm sensors (left intake rpm sensor (B6/4), right intake rpm sensor (B6/5), left exhaust rpm sensor (B6/6), right exhaust rpm sensor (B6/7)) (for model 639 left intake rpm sensor (B6/15), left exhaust rpm sensor (B6/16), right intake rpm sensor (B6/5), right exhaust rpm sensor (B6/7)) and the crankshaft sensor (B70).

Ignition at engine start

When the engine is started, the signal from the crankshaft sensor is always required, otherwise a start will not be possible.

Starter control

The solenoid switch for the starter (M1) (circuit 50) is actuated by the ME-SFI [ME] control unit via the starter relay circuit 50 (K40/9k5).

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 If release of the drive authorization system stage 3 (FBS 3 is missing), the FBS 3 bars the engine control. The starter is not actuated.

Parking shift lock

For an automatic transmission, starting is only possible in the selector lever position "P" or "N". The P/N selector lever position information is sent by the ETC control unit (N15/3) via the Control Area Network (data bus/CAN bus) (CAN).

Fuel in the engine oil

For a cold start, fuel may get into the engine oil. When the engine oil is heated, the fuel is reevaporated and is combusted via crankcase ventilation in the engine. The mixture deviation that occurs when the engine is idling can be as much as 30%.

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Lambda control corrects this deviation. Mixture adaptation saves this correction as a long-term effect. 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.