Fuel Delivery: Operation: Notes

WARNING: This page is about a different car, the 2004 Dodge Sprinter. However, it is still accessible from the selected car via links, so may be relevant.

There are several modes of operation for the Common Rail Diesel Injection System.

Pre-injection The purpose of the pre-injection function is to reduce noise and pollutants. The coolant temperature, charge air temperature and atmospheric pressure are use to correct the quantity of pilot injection. The quantity of pilot injection now determined is deducted from the quantity of main injection in order to establish whether sufficient quantity is available for the following main injection.

The rail pressure is chosen sufficiently high so that a minimum quantity is injected. If the quantity of main injection is too small the pilot injection is switched off by the ECM.

The start of actuation of pilot injection is calculated dependent on operating point, the following data being taken into account:

Shutting Off Pre-injection The pre-injection is shut off when:

The moment of pre-injection is exceeded
Engine speed too high
Pre-injected quantity too low
Main injected quantity too low
Insufficient fuel rail pressure
Engine is switched off

Fig 1: Identifying Fuel Supply Circuit

Courtesy of DAIMLERCHRYSLER CORP.

Calculating Pre-injection Quantity The pre-injection quantity is calculated on the basis of:

Engine speed
Atmospheric pressure
Coolant temperature
Boost air temperature
Fuel rail pressure

Main Injection The purpose of main injection function is to enable the injection time and injection period calculated by the ECM. The injection quantity required by the engine is divided into the per-injection and main injection quantity. If the main injection quantity computed by the ECM is too small, no pre-injection takes place.