CDI starting, function

During the starting procedure the common rail diesel injection (CDI) regulates the following functions via the CDI control unit (N3/9):

 Preglowing

 Actuation of fuel pump (M3)

 Start-readiness glowing

 Starter control

 Synchronization of injection sequence

 Start-glowing

 Start quantity control

 Afterglowing

Preglowing

For the start it is necessary to heat the glow plugs (R9) to a temperature, which heats the combustion chambers and which enables the fuel to ignite at the designated time.

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Actuation of fuel pump

The CDI control unit actuates the fuel pump via the fuel pump relay (N10/2kA) (model 203.0/2, model 209.3/4, model 211, model 219.3) or the fuel pump relay (N10/2kS) (model 221.0/2) integrated in the rear SAM control unit with fuse and relay module (N10/2). The following preconditions must be given:

 "Engine start" from drive authorization system, stage 3 (DAS [FBS] 3)

 Circ. 50 ON

 Selector lever position P or N

Start-readiness glowing

This serves to ensure that following preheating a sufficiently high combustion chamber temperature is given until the engine is started.

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Starter actuation in model 203, 209, 221

Depending on the following information the CDI control unit actuates the starter (M1) via the starter relay (N10/1kS) (model 203, 209) or circuit 50 relay, starter (N10/1kH) (model 221) integrated in the front SAM control unit with fuse and relay module (N10/1):

 DAS 3 [FBS] start approval information from the EIS [EZS] control unit (N73)

 Circ. 50 ON

 Selector lever position P or N

Starter actuation in model 211, 219

Depending on the following information the CDI control unit actuates the starter (M1) over the starter relay (N10/1kL) integrated into the driver-side SAM control unit with fuse and relay module (N10/1):

 DAS 3 [FBS] start approval information from the EIS [EZS] control unit (N73)

 Circ. 50 ON

 Selector lever position P or N

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Synchronization of injection sequence

In order to achieve correct synchronization of the fuel injection sequence to the respective cylinder, the sequence is synchronized during the engine's first revolutions. To detect the 1st. cylinder the CDI control unit requires the signal from the camshaft Hall sensor (B6/1) and the signal from the crankshaft Hall sensor (B70).

Start-up glowing

This function serves to ensure that during the starting procedure the first working cycles and the engine startup are supported.

 If during the engine start a signal has not been received from the camshaft Hall sensor, then the engine will not start.

Start quantity control

During the engine start the CDI control unit draws on the coolant temperature and motor speed to determine the start quantity and then actuates the quantity control valve (Y94), pressure regulator valve (Y74) and the fuel injectors (Y76).

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After-glowing

This function serves to ensure that once the engine has started combustion is given map-controlled support.