CDI starting, function

Common Rail Diesel Injection (CDI) controls the following functions via the CDI control unit (N3/21):

 Starter control

 Preglowing

 Start-glowing

 Afterglowing

 Actuation of the fuel pump with fuel level sensor (M3/5)

 Synchronization of the injection sequence

 Start quantity control

Starter control

The CDI control unit actuates the starter (M1) via the circuit 50 starter relay (K40/9k5) integrated in the fuse and relay box (SRB) (K40/9) depending on the messages from the EIS [EZS] control unit (N73) and, on vehicles with transmission 722.6, also depending on the messages from the ESM [EWM] control unit (N15/5).

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Preglowing

The CDI control unit receives the message "tml. 15 ON" via the Control Area Network Bus Class C (engine compartment) (CAN-C) from the EIS control unit and actuates the glow output stage (N14/2) and the preglow indicator lamp (A1e13) in line with the coolant temperature. The glow output stage actuates the glow plugs (cylinder 1 glow plug (R9/1), cylinder 2 glow plug (R9/2), cylinder 3 glow plug (R9/3) and cylinder 4 glow plug (R9/4)) on the positive side.

Start-up glowing

The CDI control unit receives the message "DAS 3 message MS" and message "tml. 50 ON" via CAN C from the EIS [EZS] control unit as well for vehicles with transmission 722.6 from ESM [EWM] control unit the message selector lever position "P" or "N".

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The CDI control unit reacts by actuating the glow output stage. The glow output stage actuates the glow plugs on the positive side.

Afterglowing

After the engine has been started, the CDI control unit determines the after-glow output stage in line with the coolant temperature. The glow output stage actuates the glow plugs on the positive side.

Actuation of the fuel pump with fuel level sensor

The CDI control unit receives the message "DAS 3 message MS" and message "tml. 50 ON" via CAN C from the EIS [EZS] control unit as well for vehicles with transmission 722.6 from ESM [EWM] control unit the message selector lever position "P" or "N". The CDI control unit then actuates the fuel pump with fuel level sensor (M3/5) via the fuel pump relay (K40/9k3) integrated in the fuse and relay box (SRB), and the fuel pump delivers the fuel to the high-pressure pump (M41) via the fuel main filter.

 Following activation of the status "circuit 15 ON", the fuel pump with fuel level sensor is actuated for t = 30 s.

Synchronization of the injection sequence

To assign the injection sequence correctly to the cylinder concerned, the sequence is synchronized at the first revolutions of the engine. The CDI control unit also needs the signals from camshaft sensor (B6/19) and from crankshaft sensor (L5/7).

The CDI control unit evaluates the inductive signal from the crankshaft sensor and the Hall signal from the camshaft sensor, i.e. the CDI control unit uses both signals to calculate when cylinder 1 reaches "ignition top dead center (TDC)".

 If no signal is supplied by the camshaft sensor when the engine is started, the engine does not start.

Start quantity control

When the engine is started, the CDI control unit calculates the start quantity depending on the coolant temperature and engine speed and then actuates the quantity control valve (Y94), the pressure regulating valve (Y74) and the fuel injectors (cylinder 1 injector (Y76/1), cylinder 2 injector (Y76/2), cylinder 3 injector (Y76/3) and cylinder 4 injector (Y76/4)).