CDI starting, function

Common Rail Diesel Injection (CDI) controls the following functions via the CDI control unit (N3/9):

 Starter control

 Preglowing

 Start-up glowing

 Afterglowing

 Actuation of the fuel pump with fuel level sensor (M3/3)

 Synchronization of injection timing

 Start quantity control

Starter control

The CDI control unit (N3/9) controls the starter (N3/9), in line with the messages from the EIS control unit (N73), and on vehicles with transmission 722.6 from the electronic selector lever module control unit (N15/5), M1 via the starter relay (N3/9) integrated in the fuse and relay block (K40/9) (K40/9k5).

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Preglowing

The CDI control unit (N3/9) receives the message "tml. 15 ON" via the Control Area Network Bus Class C (engine compartment) (CAN-C) from the EIS control unit (N73) and actuates die glow output stage accordingly (N14/2) and the preglow indicator lamp (A1e13) in line with the coolant temperature. The glow output stage (N14/2) actuates the positive side of the glow plugs (R9):

Start-up glowing

The CDI control unit (N3/9) receives the message "DAS 3 message MS" and message "tml. 50 ON" over CAN C from the EIS [EZS] control unit (N73) and, on vehicles with transmission 722.6, the selector lever position message "P" or "N" from the electronic selector lever module control unit (N15/5). The CDI control unit (N3/9) then actuates the glow output stage (N14/2). The glow output stage (N14/2) actuates the positive side of the glow plugs (R9):

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After-glowing

After the engine has been started, the CDI control unit (N3/9) determines the after-glow output stage in line with the coolant temperature.(N14/2) The glow output stage (N14/2) actuates the positive side of the glow plugs (R9):

Actuation of the fuel pump with fuel level sensor (M3/3)

The CDI control unit (N3/9) receives the message "DAS 3 message MS" and message "tml. 50 ON" over CAN C from the EIS [EZS] control unit (N73) and, on vehicles with transmission 722.6, the selector lever position message "P" or "N" from the electronic selector lever module control unit (N15/5). The CDI control unit (N3/9) actuates the fuel pump with fuel level sensor accordingly (K40/9k6) via the fuel pump relay (K40/9k6) integrated in the fuse and relay block (K40/9) K40/9k6 M3/3, which delivers the fuel via the fuel main filter to the common rail high pressure pump (M41).

Synchronization of injection timing

In order to achieve correct synchronization of injection timing for the respective cylinder, the order is synchronized during the first revolutions of the engine. For this purpose, the CDI control unit (N3/9) requires the signals from the camshaft hall sensor (B6/1) and from the crankshaft position sensor (L5).

The CDI control unit (N3/9) evaluates the inductive signal from the crankshaft position sensor (L5) and the Hall signal from the camshaft Hall sensor (B6/1), i.e. the CDI control unit (N3/9) uses both signals to calculates when cylinder 1 reaches "Ignition TDC".

 If no Hall signal is provided by the camshaft Hall sensor (B6/1) at engine start, then the engine does not respond.

Start quantity control

At engine start, the CDI control unit (N3/9) calculates the start quantity in line with the coolant temperature and engine speed and actuates the quantity control valve (Y94), the pressure regulator valve (Y74) and the fuel injectors (Y76) accordingly.