Mercedes W124

since 1985-1995 of release

Repair and car operation

W124 Mercedes
+ Governing bodies and control devices
+ 2. Maintenance (diesel engines)
+ 4. Repair of 6-cylinder petrol SOHC engines
+ 5. Repair of 6-cylinder petrol DOHC engines
+ 6. Repair of the diesel engine established in the car
+ 7. Major maintenance of engines
+ 10. System of injection of BOSCH CIS-E fuel (KE-JETRONIC)
- 11. System of injection of BOSCH HFM fuel
   11.2. General information
   11.3. Accelerator cable
   11.4. Air filter
   11.5. Casing of the air filter
   11.6. Fuel filter
   11.7. Fuel level sensor
   11.8. Fuel pump
   11.9. Fuel tank
   11.10. Throttle case
   11.11. Inlet collector
   + 11.12. Elements of system of injection of BOSCH HFM fuel
   11.13. Pressure removal in fuel system
   11.14. Adjustment of turns of idling and the contents WITH in exhaust gases
+ 12. Fuel system of diesel engines
+ 13. Fuel system of diesel engines
+ 15. System of ignition of 4-cylinder petrol engines
+ 16. System of ignition of four-cylinder petrol engines
+ 19. Mechanical transmission
+ 20. Automatic transmission

11.2. General information

The electronic control system of the BOSCH HFM engine operates system of injection of fuel and ignition.

The electronic control system of the engine consists of a fuel tank, the electric fuel pump, the fuel filter, submitting and returnable fuel hoses, the case of a throttle, the fuel highway, a regulator of pressure of the fuel, four elektronno operated fuel nozzles and the electronic control device (ECU) together with sensors, executive mechanisms and electric wires.

The fuel tank on the Sedan models and the Compartment is established vertically behind a back of a back seat. On the Versatile person models the fuel tank is established horizontally under a trunk floor. The fuel level sensor is fixed on the top part of a fuel tank and can be replaced without removal of a fuel tank.

The electric fuel pump with the circulating chamber is established under the bottom in a back part of the car. The engine of the fuel pump is constantly cooled with fuel passing through it. The fuel pump has the unidirectional valve which, blocking fuel system, supports in it pressure even after switching off of the fuel pump. The valve also isolates a fuel tank from other part of fuel system. The pump also contains a safety valve of pressure which limits pressure in fuel system.

The fuel pump submits fuel via the fuel filter to the fuel highway under the pressure exceeding pressure in fuel system. The regulator of pressure supports constant demanded pressure in fuel system and returns excess of fuel in a fuel tank on returnable топливопроводу. This constant circulation of fuel reduces temperature of fuel and предотвра щает fuel evaporation.

Fuel nozzles are an electromagician the nitny valves opened and closed by the electronic control device (ECU) which defines time of opening and duration of injection of fuel depending on turns of a cranked shaft of the engine, the provision of a butterfly valve, sizes of the arriving weight of air, temperature of air arriving in the engine, temperatures of cooling liquid and oxygen in exhaust gases on the basis of information received from sensors, established on the engine and round it.

Air in the engine arrives via the air filter with a replaceable filtering element. The temperature of air arriving in the engine is regulated by the vacuum valve established in the air filter. The vacuum valve mixes the cold air arriving in the engine, with the air warmed-up with a final collector. This valve unlike a measuring instrument of a stream of air of lopastny type is sensitive to air density. It means that when the car is maintained at big heights, air depression without necessity of use of separate barometric measurement of pressure of air is automatically considered.

Management of turns of idling is made by the control unit of turns of idling which is established sideways throttle cases, and system of ignition which regulates idling turns, changing a corner of an advancing of ignition.

The content of oxygen in exhaust gases is constantly supervised by the ECU block on the basis of signals the Lambda sensor which is established on a reception exhaust pipe. On the basis of information the Lambda sensor the ECU block defines the moment and duration of injection of fuel to support an optimum ratio of a fuel mix. Need of manual adjustment of the contents WITH in exhaust gases also disappears. Besides, for reduction of emission of harmful substances in the atmosphere, some models are equipped with catalytic converter.

On some models the ECU block also operates operation of the activated coal filter.

Detection of malfunctions on an electronic control system of the HFM engine possibly only with use of the special diagnostic equipment.


The fuel system is under constant pressure, even after engine switching off therefore at carrying out any works on fuel system it is necessary to remove pressure.

For prevention of possibility of casual short circuits of an electric chain and damage of electronic components of system of injection of fuel always remove a weight wire from the accumulator.


Gasoline extremely fire - also is explosive, therefore it is necessary to show care at work on any part of fuel system.

Works on fuel system are necessary for making in well aired room for what it is possible to open all windows and doors for draft creation.

At work on fuel system do not use open fire, electric welding and tools, at work with which sparks can be formed. Check that in close proximity to a workplace there is a charged fire extinguisher.

For protection of eyes against fuel hit in them use points. At fuel hit on skin wash out this place a plentiful quantity of water.

The capacity in which there was a fuel, contains pairs of fuel and is potentially explosive.

At work with fuel system observe purity as the dirt which has got to channels of fuel system, can block them that will break normal operation of the engine.