Contents: Visual inspection of the injection…↡ Engine Shutdown System Malfunctions ↡ Checking air connections for…↡ Injector malfunctions ↡
Most work related to the repair and maintenance of the injection system should be carried out by specialists at the service station. They have the necessary diagnostic devices and the corresponding equipment. In case of malfunctions in the electronic control, it is sometimes necessary to conduct a series of specialized tests to find the cause of the malfunction. This is the only way to determine the damage to the corresponding units and parts and avoid more expensive repairs. You can independently check the malfunctions that occurred when the control unit malfunctioned, the condition of the sensors, switches and cable connections.
Sequence of works
1. Check if the fuse is securely installed and if the relay is connected to the connectors and pins.
2. Make sure the heating system is working properly.
3. Check the fuel supply system.
4. Perform a visual inspection of the injection system.
Fig. 4.79. Control unit diagnostics
5. If this does not bring results, submit the control unit for testing and memory control.
From the point of view of diagnostics, the control unit depends on the engine operating mode. When driving, errors are received in the memory storage device, when stopping and disconnecting the battery, they are deleted. The EDS control system is equipped with an additional source for the memory system, this ensures that even minor faults that occur in a short time are entered into the memory. By comparison, only those faults that must be immediately eliminated are mainly remembered. Minor faults that occur very rarely are erased by the memory. "Reading" of these errors is possible at the Mercedes station using a special tester (HHT) (Fig. 4.79). There is also a set of additional characteristics and tests.
Visual inspection of the injection system
"15,000 km"
1. Check the 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 the fuel lines for leaks and the correct connection of the fuel return line.
5. Check all electrical connectors and the reliability of their connection in the injection system wiring.
Engine Shutdown System Malfunctions
If the system is faulty or de-energized, the engine will not turn off. A system fault is also indicated by the fact that the engine does not start even though the injection system is working properly and there is enough 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 switch unit.
3. If there is no click, this indicates a problem with 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 not installed tightly.
6. If there is voltage, there may be a malfunction in the shutdown system itself.
Checking air connections for tightness
If the connections are loose, so-called extraneous air enters the suction system or, conversely, some air escapes from the injection system into the atmosphere. This leads to a violation of the calculated operating mode and, as a result, to incorrect injection dosing. As a rule, the engine operation with interruptions indicates a leaky connection.
(Material taken from a web resource: «mercedesman.ru»)
"15,000 km"
1. Check the vacuum hoses connected to the intake manifold and injection system for cuts and damage, and for tightness.
2. Warm up the engine and let it idle.
3. Using a spray can, spray fuel onto the intake system flanges, intake duct gaskets, and vacuum line pipes. If the engine speed changes when spraying the specified connections, the connection is not sealed.
Injector malfunctions
The engine runs rough, bearing noise, ringing sounds are heard, and blue smoke comes out of the muffler from time to time. If such signs occur, it is necessary to disconnect the pipes leading to the injectors one by one. If there is no change in engine operation when one of the pipes is disconnected, then presumably this injector is not working. Injector failure may be caused by contamination. After the car has been parked for a long time, the injector needle may "stick" to the body. With long-term use of injectors, their injection pressure decreases. Service stations have a special device that determines the suitability of the injector. If the injector starts working at a pressure below 100 bar, it must be replaced.