CDI starting, function

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

 Preglowing

 Actuation of fuel pump (M3)

 Start-readiness glowing

 Starter control

 Synchronization of the 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 over the integral fuel pump relay (N10/2) in the rear SAM control unit with fuse and relay module (N10/2kA). The following requirements must be present:

 "Engine start" from the drive authorization system stage 3 (DAS 3)

 Circuit 50 ON

 Selector lever position "P" or "N"

Start-readiness glowing

This guarantees that following pre-glowing, a sufficiently high combustion temperature is present until the engine starts.

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Starter control

Depending on the following information, the CDI control unit actuates the starter (N10/1) via the starter relay (N10/1kL) integrated in the driver SAM control unit with fuse and relay module (M1):

 DAS 3 "engine start" from the EIS control unit (N73)

 Circuit 50 ON

 Selector lever position "P" or "N"

Synchronization of the injection sequence

In order to achieve correct synchronization of the fuel injection sequence for the respective cylinder, the order is synchronized during the first revolutions of the engine. To detect cylinder 1, the CDI control unit requires the signal from the camshaft Hall sensor (B6/1) and the signal from the crankshaft position sensor (L5).

Start-up glowing

During start, this function assists with the first working cycles and speeding up of the engine.

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

Start quantity control

At engine start, the CDI control unit 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.

After-glowing

This function assists with combustion by performance mapping following a successful engine start.