Sequence of work
1. Check if the fuse is secure, if the relay is connected in the connectors and trunnions.
2. Make sure the heating system is working properly.
3. Check the fuel supply system.
4. Perform a visual inspection of the injection system.
Pic. 4.79. Control unit diagnostics
5. If this does not work, hand over the control unit to check and control the memory.
From the point of view of diagnostics, the control unit depends on the operating mode of the engine. When moving to the memory drive, errors are accepted, when the battery is stopped and disconnected, they are deleted. The EDS control system is equipped with an additional source for the memory system, which ensures that even minor faults that occur in a short time are stored in the memory. By comparison, in general, only those faults are stored that must be rectified immediately. Minor malfunctions that occur very rarely are erased by the memory. «Reading» these errors are possible at the Mercedes station using a special tester (HNT) (pic. 4.79). There is also a set of additional characteristics and tests.
Visual inspection of the injection system
"15,000 km"
1. Check air hoses for leaks.
2. Check the fit and condition of the brake booster hose.
3. Check the condition of the crankcase ventilation hoses.
4. Check fuel lines for leaks and correct fuel return line connection.
5. Check up all electrosockets and reliability of their connection in electroconducting of system of injection.
Malfunctions of the engine shutdown system
If the system is faulty or has no power, the engine will not turn off. A system malfunction is also indicated by the fact that the engine does not start with a good injection system and a sufficient amount of fuel.
"15,000 km"
1. Check the reliability of the connection and the wire itself to the engine shutdown system.
2. When turning the ignition key, a click should be heard in the area of the shutdown unit.
3. If there is no click, this indicates a malfunction of the power supply or the system itself.
4. Turn on the ignition and check for voltage at the system connector.
5. If there is no voltage, the cable is faulty or the fuse is loose.
6. If there is voltage, there may be a malfunction of the shutdown system itself.
Checking air connections for tightness
In case of loose connections, so-called foreign air enters the suction system or, conversely, part of the air from the discharge system escapes into the atmosphere. This leads to a violation of the calculated mode of operation and, as a result, incorrect dosing of the injection. Leaky connections are usually indicated by intermittent engine operation.
"15,000 km"
1. Check the vacuum hoses connected to the intake manifold and injection system for cuts and damage, as well as tight fit.
2. Warm up the engine and leave it to idle.
3. Use a spray can to spray the suction flanges, suction port gaskets, and vacuum line piping with fuel. If the engine speed changes when these connections are sprayed, the connection is leaking.
Injector malfunctions
The engine runs hard, bearing noise, ringing sounds are heard, blue smoke is emitted from the muffler from time to time. With such signs, it is necessary to sequentially, one by one, disconnect the pipelines leading to the nozzles. If, when one of the pipelines is disconnected, there is no change in the operation of the engine, then this nozzle is presumably not working. Injector failure may be caused by contamination. After the car has been parked for a long time, the nozzle needle may «take a liking» to the hull. With long-term operation of the injectors, their injection pressure decreases. At service stations there is a special device that determines the suitability of the nozzle. If the nozzle starts working at a pressure below 100 bar, it must be replaced.