The illustration shows the MPI/MPFI injection system. The numbers indicate:
1 - fuel pressure regulator;
2 - fuel distributor;
3 - injection nozzle.
Additional signals
This diagram shows the ignition and injection system in detail using the example of an MPFI system with an exhaust manifold pressure sensor. On the left side are sensors and sensors that affect the behavior of the control unit. On the right are the components of the ignition and injection systems to which the control unit sends its commands.
Control block
Between incoming (from various sensors) information and injection nozzles is located in the control unit. It allows the engine, depending on the actual load and temperature conditions, to receive a precisely defined amount of fuel. To achieve this, the control unit varies the duration of the opening of the solenoid driven injectors. Since the pressure in the fuel supply system remains practically unchanged at all times, the amount of fuel injected can only be controlled by changing the injection duration. Where does the control unit get the information according to which it sets this injection duration? Various sensors are responsible for this:
Only 2.8-liter engine with MPI injection system: air mass meter; it gives information about the amount of air that has entered.
2.6L MPFI engine only: Exhaust manifold temperature sensor; it reports in conjunction with the exhaust manifold pressure sensor (in the control unit) the quantity/mass of the incoming air.
Coolant temperature sensor; it reports the temperature of the engine.
throttle potentiometer; it provides information about the load on the engine.
RPM sensor; speed signal for MPI/MPFI ignition/injection system. О Ignition timing sensor; it reports the position of the crankshaft. So the control unit will know which cylinder is next for ignition or injection.
Start signal comes from terminal 50 (lock-switch ignition and starter).
Lambda probes report whether the composition of the mixture is correct.
Indicators from knock sensors, from the transmission, from the tachometer, from the air conditioner.
Injection nozzles
There is one injection nozzle in the intake manifold of each cylinder of the engine. They deliver the required amount of fuel to the corresponding cylinder at the moment. The nozzles are driven by an electromagnet. In this case, the atomizer needle rises from its seat by about 0.1 mm - fuel can flow. Each individual injection nozzle is controlled precisely in the injection cycle. This means that the injected fuel does not even have time to condense on the walls of the intake manifold (no fuel loss).
Fuel distributor
It is designed to evenly supply fuel to all injection nozzles. The fuel distributor also acts as a fuel accumulator, thereby preventing pressure drops. An interesting U-shaped pipe, which allows the supply of fuel to all six nozzles.
Fuel control regulator
It is located on the rear right of the fuel distributor and should - as its name suggests - maintain a constant level of pressure in the fuel distributor. This is done by means of a more or less strong outflow of fuel back into the fuel tank through the drain line. If more fuel leaves the drain line, then the pressure decreases; if less, the pressure rises. The connection of the vacuum line to the pressure regulator also provides information on the engine load. At full load, the regulator increases the pressure even more, injecting more fuel to achieve maximum engine power.
Fuel pump and relay
You will learn more about the solenoid fuel pump, fuel pump relay and other MPI / MPFI relays in the chapter «Fuel tank and fuel pump».
Air mass meter (MPI only)
In the path of the air flow is a wire heated electrically. Depending on the injected amount, the air flow changes, which leads to a more or less strong cooling of said wire. A change in temperature leads to a change in the electrical resistance of the wire, which is measured by the control unit.
Pressure meter (MPFI only)
The exhaust manifold pressure sensor is located in the MPFI control unit. The pressure in the exhaust manifold is the main type of information for the control unit for calculating the engine load. It affects the duration of the injection and the ignition timing.
Temperature sensor (MPFI only)
The intake air temperature sensor is screwed into the intake duct of the third cylinder. It serves as a source of information for the control unit to calculate the load on the engine. At high intake air temperature (which is equivalent to low air density) it is necessary, for example, to shorten the injection duration and slightly shift the ignition timing to the side «Later».
Throttle housing
Where the intake air flow enters the engine's exhaust manifold, there are two throttle valves in the same housing. The smaller of the flaps is connected by a cable to the accelerator pedal. It doses the intake air flow into the engine up to the half load position. By further depressing the accelerator pedal, the traction lever opens the second, larger flap until both flaps are fully open in the full load position.
Throttle Potentiometer
The throttle valve potentiometer is actuated by the throttle valve shaft. It determines the position of the throttle valve at a given time and transmits this information to the control unit in the form of electrical resistance. The control unit needs this load information to regulate the idle speed, select the ignition characteristic and calculate the injection duration.
Idle speed stabilization valve
This valve constantly ensures a constant engine speed in idling mode - it does not matter whether the engine is cold or warm, whether powerful consumers of electricity such as air conditioning are on or off. The valve itself is an executing organ. The control center is the injection system control unit MPI or MPFI. It compares the actual RPM with the target RPM and thus provides finely coordinated opening and closing of the control valve to balance the RPM. In this case, the cross-section of the additional air channel, laid around the throttle valves, varies. When the duct is open, more air is let in, thus the air mass meter or exhaust manifold pressure sensor due to the increase in air «thinks», that the throttle is open. Which in turn gives rise to the injection system to increase the amount of incoming fuel. In different injection systems, different valves operate to stabilize the speed: in the MPI injection system - smoothly regulating; in the MPFI injection system - driven by a so-called stepper motor. This latter regulates the opening of the channels in small, finely adjusted steps.
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