General description of the diesel fuel injection system (Mercedes-Benz Sprinter 903)

2.3L engine (index 601)

The booster pump pumps diesel fuel from the tank and feeds it through the fuel filter under low pressure to the high-pressure fuel pump. From there, the fuel is fed to the injectors through high-pressure fuel lines. A distinction is made between direct and split injection (using pre-chambers). The engines of these models use a pre-chamber injection system. It differs in that the fuel is injected into the pre-chamber, located in the cylinder head and connected to the main combustion chamber. In the pre-chamber, the fuel ignites and the combustion process begins. As a result of the resulting pressure, the burning fuel enters the main chamber, where the combustion process is completed.

The high-pressure fuel pump is a piston-type pump. It is located on the left side of the cylinder block and is driven by the camshaft drive chain. For each engine cylinder, the injection pump has a separate section consisting of a plunger and a cylinder. The plunger of this section is controlled by the corresponding cam. The plunger is carefully adjusted to the cylinder, therefore ensuring tightness at high pressure. The fuel injection pump lubrication system is connected to the engine lubrication system. A sealing ring is installed at the connection between the fuel injection pump flange and the cylinder block.



The fuel supply volume is regulated by a spiral groove on the plunger. Depending on the angle of rotation of the plunger, more or less fuel is supplied. The fuel pressure generated by the injection pump plunger lifts the injector needle and opens the injection hole. Through the nozzle, atomized fuel is injected into the pre-combustion chamber. At the moment when the plunger spiral groove opens the return pipeline channel, the pressure drops and the nozzle needle drops under the action of the spring.

On the reverse side of the injection pump is the pump control mechanism, which is a system of levers and springs, and a centrifugal regulator on the rear end of the pump camshaft. Engine stop diaphragm mechanism, idle speed increase diaphragm mechanism (if it is installed) and the stop lever accordingly affect the operation of the regulator. The regulator controls the position of the fuel injection pump rack, thus regulating the fuel supply. To supply fuel from the tank to the high-pressure fuel pump, a mechanically driven piston pump is used. The booster pump does not have manual pumping, as was the case with diesel engines of previous releases.

2.9L engine (index 602)

The engine is equipped with a direct injection system with electronic control, the two most important elements of which are the distribution fuel pump and the electronic control unit.

The control unit regulates the fuel supply depending on the position of the fuel supply pedal and the technical condition of the engine.

Fuel supply and the start of injection are regulated by the pump depending on the following factors:

• accelerator pedal position;
• loads (technical condition) engine;
• atmospheric pressure;
• intake air temperature;
• control unit settings.

The engine stops as a result of the fuel supply from the pump being stopped.

An exhaust gas recirculation system and a catalytic converter can be installed as standard, but cars are also sold without these devices. In turn, the operation of the injection system control unit on the 2.9 l engine does not affect the functioning of other devices. The glow plugs are controlled by a separate control unit to facilitate starting. The control unit is equipped with a memory device for recording codes of occurring faults, information about which is stored in it even when the ignition is off and the battery is removed.

In case of serious faults, the indicator lamp in the instrument cluster lights up. Malfunctions may occur as a result of a malfunction:

• crankshaft position sensor;
• Fuel injection pump;
• pump distributor position sensor;
• fuel supply valve;
• check valve;
• regulator valve.

Fuel tank and fuel lines

The fuel tank is located under the floor of the car. Its capacity depends on the modification and is indicated in the user manual. The fuel lines are designed for high pressure, so they are made of durable material and connected with clamps and screw clamps. A distinction is made between direct and return pipelines for returning excess fuel to the tank. Fuel is supplied to the high-pressure fuel pump by a booster pump. A fuel level sensor is installed on the top side of the fuel tank.



A special fuel tank ventilation system is also provided. A ventilation hose is attached to the filler neck and leads to the top of the tank. Air escapes through it when fuel is added to the tank. Air flows through it and back, when fuel is consumed during engine operation, so that a vacuum does not form.

Fuel saving methods

Accelerate smoothly, shift into a higher gear as early as possible. Once you reach your desired speed, select the optimal gear and allow the vehicle to move with the least amount of effort applied to the accelerator pedal. Maximum revs are only permitted when overtaking or driving in heavy traffic. In addition, turn off the engine when stopping in front of a barrier, traffic light or in a traffic jam - even a 5-7 second pause saves fuel.

Diesel fuel

Diesel fuel is specially designed for diesel engines. Due to its high flammability, the process of spontaneous combustion occurs in a matter of fractions of a second. The ability of fuel to self-ignite is characterized by the cetane number, a relative indicator derived from laboratory studies. The substance cetane with very high flammability is assigned an index of 100, while the least flammable methylnaphthalene is assigned an index of 0. The cetane number shows the content (in percent) cetane in a given volume of a given fuel. For diesel fuel it should be 45.

Diesel fuel mainly consists of so-called paraffins. These hydrocarbons are highly flammable, but begin to crystallize at low temperatures. Individual crystals quickly join together to form complex compounds. As the temperature drops further, many crystallized chains form that do not pass through the fuel filter. Manufacturers solve this problem by adding special additives. Chemical additives prevent the formation of paraffin chains, preventing individual crystals from joining together. Individual crystals are small enough to pass through the pores of the filter. As a result, the fuel reaches the injection pump. General recommendations for filling the vehicle with the appropriate types of diesel fuel:

• fill with diesel fuel appropriate for the season, with a cetane number of at least 45 (according to DIN 51 601);
• for summer diesel fuel, additives are not needed. It begins to crystallize at temperatures below -2°C;
• winter diesel fuel with the addition of additives is used at temperatures down to –22°C (DIN standard –12°C).

Material taken from a web resource (mercedesman.ru)

Summer diesel fuel in winter

If the vehicle has not been used for 6 months or more, there may be a situation where you need to drive on summer diesel fuel in sub-zero temperatures. In this case, it is necessary to use fuel thinner additives, which are sold at gas stations or in auto stores. Consult with the seller about the appropriate type of additive and carefully read the instructions for its use. When adding the additive, the fuel should be at room temperature. If the fuel in the tank has already thickened, adding an additive will not help. In this case, you need to tow the car to a warm garage, where the crystallized paraffins will dissolve again, then you can pour in the additive.

Precautions when handling fuel

The fuel is flammable. Therefore, during repair work, be careful when working with the engine fuel system. Particular care must be taken when draining fuel. When handling fuel, the following precautions should always be observed:

• remove the terminals from the battery and insulate them;
• do not drain fuel in a closed area. To do this, you need to use a special pump. Do not do this through the fuel level sensor hole or by sucking with your mouth through one of the hoses - this is dangerous due to possible poisoning by toxic components of the fuel;
• a class B fire extinguisher should be kept on hand;
• do not drain fuel over the inspection pit. Fuel vapors are heavier than air, so they will take a long time to evaporate from the pit. The dangerous consequences in this case are harm to health when inhaled, as well as high explosive hazard;
• when working with fuel, make sure that there are no electrical appliances, open flames or sparks in the room;
• only specially designed containers, tightly closed, fire-proof and with a pressure equalizer plug, must be used for fuel;
• an empty tank contains fuel vapors, which are also very dangerous. Therefore, all further work must be carried out very carefully.

Fuel drain

The fuel tank does not have a drain hole. Since the supply and return fuel lines are located on the top of the tank, draining the fuel is not an easy procedure. Fuel drainage is carried out as follows:

• insert the hose as deep as possible into the filled tank through the filler neck;
• press the opening of the hose tightly with your finger. The drain container must be below the level of the bottom of the tank. To start draining, pull the hose out slightly and direct it into the container. If the hose is long enough and well immersed in fuel, it should begin to drain. Sucking fuel with your mouth is dangerous to your health.

If there is little fuel left in the tank, this method may not be effective. In this case, a special pump must be used for pumping out.

Cleaning of exhaust gases of diesel engine

A catalytic converter is installed in the exhaust system of a diesel engine. It reduces hydrocarbon and carbon monoxide emissions by up to 50%. The catalytic converter does not filter solid particles, but it plays a significant role in reducing their share in exhaust gases. Gaseous hydrocarbons tend to adhere to solid particles, thereby increasing the volume of particulate matter emitted. But since the hydrocarbons are oxidized in the neutralizer, they can no longer settle on the solid particles.

Exhaust gas recirculation system

The exhaust gas recirculation system, designated as AGR (English abbreviation - EGR), serves to reduce the content of nitrogen oxides in the exhaust gases. Some of the gases are diverted through a valve-controlled system and fed back into the intake manifold, reducing the temperature in the combustion chamber, which leads to a reduction in the content of nitrogen oxides. The operation and control of the recirculation system is controlled by the electronic injection self-diagnosis system (on a 2.9 l engine).

This manual does not cover the operation of the system in detail.