- 1 - Engine speed sensor
- 2 — Ignition moment sensor
- 3 - Hall sensor
- 4 - Coolant temperature sensor
- 5 - Intake air temperature sensor
- 6 - Throttle potentiometer and idle switch
- 7 - Knock sensor I
- 8 - Knock sensor II
- 9 - Lambda probe I
- 10 - Lambda probe II
- 11 - Injection valves
- 12 - Power output stage
- 13 - Dual ignition coils
- 14 — the Valve of stabilization of idling
- 15 - The solenoid valve of the carbon filter system
- 16 - Control unit for heating lambda probes
- 17 - Fuel pump relay
This diagram illustrates the electrical side of the ignition/injection system, in this case an MPFI with an intake manifold air pressure sensor. On the left side are sensors and sensors that affect the behavior of the control unit. On the right are those ignition and injection units to which the control unit sends its signals.
Fuel side of MPI/MPFI ignition/injection system
- 1 - fuel pressure regulator;
- 2 - distribution tube of fuel;
- 3 - injection valve.
Control block (2) MPI/MPFI ignition/injection system is located in the electronic box on the left rear in the engine compartment (in the so-called humidification tank). In the bracket next to the control unit, here in the engine with a displacement of 2.6 liters, there is a relay (1) heating lambda probes.
Left: injection valves (1, 2 and 3) in a six-cylinder engine, they are located in groups of three to the right and left of the central intake manifold.
Right: rear right in the engine compartment is a fresh air flow meter (1), in an engine with a displacement of 2.8 liters flanged to the air filter housing. Numeric «2» connector is marked.
Control block
between incoming information (from various sensors) and injection valves is an electronic control unit. Depending on the existing load conditions and temperature, it sends a very specific amount of fuel to the engine. To this end, the control unit varies the opening time of the electromagnetically controlled injection valves. The amount of injected fuel can only be changed by the duration of the injection. Information for determining the duration of the injection enters the control unit from various nodes, these are:
- Only on 2.8l engine with MPI: fresh air flow meter; from it receives information about the amount of air intake.
- Only in the 2.6 engine with MPFI: intake air temperature sensor; in combination with an air pressure sensor in the intake manifold (in the control unit) it gives a comparative value of the amount/mass of air taken in/th.
- Coolant temperature sensor; it provides a comparative value for the engine temperature.
- throttle potentiometer; from it receives information about the load on the engine.
- RPM sensor; it transmits a signal about the number of revolutions of the crankshaft.
- The signal to start the engine comes from terminal 50 of the ignition switch (starter).
- Lambda probes send a signal about the correct composition of the fuel-air mixture.
- Other influences come from: knock sensors, gearbox, speedometer and, if available, the air conditioner.
Injection valves
In the suction channel of each engine cylinder, one injection valve is located. It supplies each cylinder with the required amount of fuel at the moment and at the same time provides a fine atomization of gasoline.
The valves are actuated electromagnetically. In this case, the metering needle rises in its seat by about 0.1 mm - fuel can flow.
Fuel distribution pipe
It serves to evenly supply fuel to all injection valves. In addition, the distribution tube functions as a collector and therefore does not allow pressure fluctuations. The annular shape of the tube is interesting, allowing fuel to be supplied to all six valves.
Fuel pressure control
It is located on the rear right side of the fuel rail and must maintain a constant fuel pressure in the rail. It does this by increasing or decreasing the amount of fuel flowing through the recirculation tube. If more fuel is returned, the pressure drops; with a small return of fuel, it rises.
By connecting a vacuum hose, the pressure regulator simultaneously receives information about the state of the engine load. At full load, it raises the pressure a little more. As a result, more fuel is injected that the engine needs to achieve full power.
Fuel pump and relay
You will learn more about the electric fuel pump, fuel pump relay and other MPI/MPFI relays in chapter Fuel tank and fuel pump.
Fresh air pressure meter
MPI only
A wire is placed in the intake air stream, which is heated electrically. Depending on the mass of air taken in, the air flow changes, which cools the wire more or less. A change in temperature causes a change in the resistance of the wire, and this is measured by the control unit.
Intake manifold air pressure sensor
MPFI only
The intake manifold air pressure sensor is located in the MPFI control unit. The intake manifold and sensor are connected by a thin hose. For the control unit, the air pressure in the intake manifold is the most important information for calculating the load on the engine. This has an effect on the duration of the injection and on the ignition timing.
Fresh air flow temperature sensor
MPFI only
The intake air temperature sensor is screwed into the intake port of the third cylinder (rear right). In addition to the air pressure sensor, it serves as a control unit for calculating the engine load. At high intake air temperatures (equals low air density) the injection time, for example, should be shortened and the ignition timing shifted slightly more in the direction «later».
Throttle valve
Where the fresh air flow enters the engine intake manifold, there are two throttle valves in the fitting. The smaller one is connected by a throttle cable to the pedal in the cabin. It doses the flow of intake air into the engine to the half-throttle position.
As the pressure on the gas pedal increases, the linkage system opens a second, larger flap until both throttles are fully open at full throttle.
Throttle Potentiometer
The throttle valve potentiometer is actuated by its shaft. The potentiometer determines the position of the throttle valve at the moment and sends a signal in the form of an electrical voltage to the control unit. This load information, among other signals, is used by the control unit to adjust the idle speed, select the ignition characteristic and calculate the injection duration.
Idle stabilization valve
As the name implies, this valve provides a constant idle speed - no matter if the engine is warm or not, power consumers are connected (air conditioner) or not.
The valve is only an actuating element. The brain of regulation is the MPI or MPFI control unit. It compares the current RPM with the nominal RPM and provides finely tuned opening and closing of the control valve to match the RPM. This changes the cross section of the auxiliary air duct that bypasses the throttle valve. If the auxiliary duct is open, more air is drawn in, and therefore the fresh air flow meter «thinks», that the throttle is open. This, in turn, causes the injection system to direct the right amount of fuel, which leads to an increase in engine speed.
It should also be noted that various idle speed stabilization valves are used: stepless control valve MPI; valve driven by a so-called stepper motor with MPFI. The latter modifies the bypass opening in fine, finely tuned steps.
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