The multi-point injection system creates the ideal prerequisites for highly efficient mixing. Each cylinder has a separate valve injector that injects fuel directly in front of the intake valve. The nozzles are controlled by electronic circuits, they have an electromagnetic drive and operate in intermittent mode.
The principle of multi-point injection in a 4-cylinder engine: 1 - fuel, 2 - air, 3 - throttle valve, 4 - intake gas pipeline, 5 - injectors, 6 - engine.
Sectional valve nozzle (principle): 1 - O-rings, 2 - filter mesh, 3 - valve body with electrical connecting element, 4 - coil, 5 - spring, 6 - valve needle with solenoid armature, 7 - valve seat with washer for injection hole. The figure shows a Bosch injector designed for Motronic control systems.
Elements of the Motronic system for ASN engines (3.0 L, 6 cylinders): 1 - Solenoid valve N80 for activated charcoal tank, 2 - Air mass meter G70 with intake air temperature sensor G42, 3 - Hall sender G300 for exhaust camshaft (1st row of cylinders), 4 - Hall sender G40 for intake camshaft (1st row of cylinders), 5 - Pressure sender G294 for brake booster, 6 - Hall sender G163 for intake camshaft (2nd row of cylinders), 7 - Hall sender G301 exhaust camshaft (2nd row of cylinders), 8 - ignition coils with a powerful final stage (2nd row of cylinders: cylinders 4, 5 and 6), 9 - electronics unit in the battery section (including engine control unit J220), 10 - pump V192 for the brake booster, 11 - valves N208 and N319 for adjusting the intake and exhaust camshaft (2nd row of cylinders), 12 - valve injectors (2nd row of cylinders: cylinders 4, 5 and 6), 13 - valve injectors (1st row of cylinders: cylinders 1, 2 and 3), 14 - valves N205 and N318 for adjusting the intake and exhaust camshaft (1st row of cylinders), 15 - ignition coils with a powerful final stage (1st row of cylinders: cylinders 1, 2 and 3), 16 - engine V101 for auxiliary air pump, 17 - oxygen sensor G39 with heating device Z19 in front of the catalytic converter (1st row of cylinders), 18 - holder for detachable connections, 19 - oxygen sensor G130 with heating device Z29 after the catalytic converter (1st row of cylinders), 20 - Coolant temperature sender G62, 21 - Throttle valve control unit 338, 22 - Air boost valve N112, 23 - Engine speed sender G28, 24 - Bracket for plug connections, 25 - Accelerator position senders G79 and G185, 26 - fuel pump relay L 7, 27 - brake light switch F and brake pedal position sensor F47, 28 - clutch pedal position sensor F36, 29 - combined instrument panel with warning lights, 30 - oxygen sensor G131 with heating device Z30 after the catalytic converter (2nd row of cylinders), 31 - oxygen sensor G108 with heating device Z28 in front of the catalytic converter (2nd row of cylinders), 32 - fuel pressure regulator, 33 - knock sensor 2/G66 (2nd row of cylinders), 34 - valve N156 for switching the intake gas line with a variable path length, 35 - knock sensor 1 / G61 (1st row of cylinders), 36 - circulation pump of the liquid cooling system V51, 37 - ground connection (on the right engine mount).
Elements of the Motronic system for ALT engines (2.0 l): 1 - oxygen sensor G130 (55 Nm) after the catalytic converter, 2 - boost air valve N112, 3 - coolant temperature sender G62 (9 Nm), 4 - valve 1 for adjusting the camshaft N205, 5 - engine speed sender G28. 6 - Fuel pressure regulator, 7 - Throttle valve control unit J338, 8 - 3-pin connector for knock sensor G61, 9 - 4-pin connector for oxygen sensor G130, 10 - 3-pin connector for engine speed sensor G28, 11 - 3-pin connector for knock sensor G66, 12 - six-pin connector for oxygen sensor G39, 13 - engine control unit J361, 14 - relay J299 for auxiliary air pump and power supply relay for engine control unit, 15 - brake booster vacuum pump, 16 - vacuum box for switching the intake manifold, 17 - solenoid valve N156 for switching the intake manifold with variable path length, 18 - intake air temperature sender G42, 19 - phase sensor (Hall Sensor) G40 valve injectors (N30...N33), 20 - ignition coils, 21 - oxygen sensor G39 (55 Nm), 22 - air mass meter G70, 23 - solenoid valve N80 for activated carbon tank. The following parts are not shown in the illustration: brake light switch F and brake pedal position sensor F47 on the pedal bracket, diagnostic socket on the driver's side, fuel pump relay on the relay holder behind the storage box on the driver's side, clutch pedal position sensor F36 on the pedal bracket next to the clutch pedal, the accelerator pedal position senders G79 and 185 in the housing on the accelerator pedal, as well as the signaling device for the electronic accelerator pedal in the combined instrument panel.
Elements of the Motronic system for AVJ engines (1.8L turbocharged): 1 - solenoid valve N80 for activated carbon tank, 2 - oxygen sensor G39 (55 Nm), 3 - oxygen sensor G130 (55 Nm), 4 Combination valve for auxiliary air charging, 5 Coolant temperature sender G62, 6 Engine speed sender G28, 7 Secondary air charging valve N112, 8 and 9 Holders for plug connections, 10 and 11 Electronics box in battery section (including engine control unit J220 and two current relays: J271 for Motronic, J299 for auxiliary air pump, 12 charge pressure sender G31, 13 throttle valve control J338, 14 intake air temperature sender G42, 15 wastegate valve N249 for turbocharger, 16 - knock sensor G61, 17 - knock sensor G66, 18 - Hall sender G40, 19 - valve injectors N30-N33, 20 - ignition coils, 21 - solenoid valve N74 for boost pressure limitation, 22 - air mass meter G70, 23 - V101 motor for auxiliary air pump. The following parts are not shown in the illustration: brake light switch F and brake pedal position sensor F47 on the pedal bracket, diagnostic socket on the driver's side, fuel pump relay on the relay holder behind the storage box on the driver's side, clutch pedal position sensor F36 on the pedal bracket next to the clutch pedal, the accelerator pedal position senders G79 and G185 in a housing on the accelerator pedal and the electronic accelerator pedal indicator in the combined instrument panel.
External mixing
In the petrol versions of the Audi A4, which have prevailed to this day, external mixing is still used: the fuel is injected ahead of the intake valves. In this case, the air-fuel mixture charged into the cylinder is, as a rule, distributed homogeneously over the entire combustion chamber.
Even in the case of such indirect multi-point injection, due to the fact that the intake and exhaust valves are located next to each other, the mixture does not have to travel a long path in the gas pipeline. The risk of gasoline depositing on the intake pipe wall, especially when the engine is cold, is reduced.
Electronic fuel injection systems (Motronic from Bosch or Simos from Siemens) differ depending on the type of engine, but their principle of operation is the same. The systems differ from each other in terms of the design of individual parts, parameters and installation location. This is clearly shown in the following figures, which show three variants of the Motronic system.
The drawings showing Motronic systems and their individual components clearly show the incredible complexity of modern engines and engine management systems. Without special aids and expensive instrumentation, neither qualified maintenance nor meaningful repair of these systems is possible. Rather, we wanted to demonstrate how a meaningful injector test is performed using the appropriate measuring instruments.
The instructions for replacing the throttle cable, which have always been given in such publications, are no longer available, since the Audi A4 has only an electronic accelerator pedal. Therefore, we only inform you about the removal and installation of the accelerator pedal module.
It is important, at least in general terms, to imagine the interaction of the individual elements of the Motronic system, and also to know where they are approximately installed. This will make it easier for you to understand the fault diagnosis data that is carried out in the workshop and allow you to exchange opinions with specialists on repairs. Often, replacement of individual parts and entire assemblies is indispensable. For this reason, in our book, we also provide a drawing with details of the intake manifold changeover as an essential part of the ignition and fuel injection system of the six-cylinder ASN engine.
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