The fuel injector is the most important component in the fuel supply system. It is essentially a solenoid valve. When the ECU issues a command, the solenoid coil is energized to open the needle valve and inject accurate metered fuel into the front of the intake valve (in-cylinder injection) except).
Fuel Injector Function
First, Fuel Injector Definition. Fuel injector is the abbreviation of fuel electric fuel injector, also known as fuel electric nozzle, which is mainly used to complete the task of injecting fuel into the engine intake manifold or combustion chamber.
The fuel injector is mainly composed of a valve body, a needle valve, a return spring, an armature, a solenoid coil, an oil inlet filter and a harness connector. Injectors can be divided into shaft needle type, ball valve type and sheet valve type according to their different structures; according to different resistance values, they can be divided into low resistance type and high resistance type, and the resistance value of low resistance type injector is 2 ~ 3Ω The resistance value of high resistance type fuel injector is 13 ~ 17Ω; it can be divided into voltage drive and current drive according to different driving methods. Voltage drive is suitable for high resistance type fuel injector and low resistance type fuel injector with additional resistance connected in series. Current drive is suitable for low resistance type injectors.
(1) Shaft needle fuel injector
Shaft needle fuel injector is mainly composed of filter screen, return spring, solenoid coil, needle valve and armature, as shown in the figure below. Its characteristic is that the shaft needle can make the fuel be ejected in a ring shape, which is conducive to atomization; the needle valve reciprocates in the nozzle, which is not easy to cause the nozzle to block.
(2) Ball valve fuel injector
The ball valve fuel injector is similar to the pin needle injector, the ball valve stem is a hollow rod, and the weight is light. In addition, due to the self-centering effect of the ball valve, it has a high sealing performance.
(3) Slice valve fuel injector
When the solenoid is not energized, the valve plate is pressed against the valve seat by spring force and fuel pressure. When the ECU control device energizes the electromagnetic coil, the electromagnetic force overcomes the sum of the spring force and hydraulic pressure, causing the spring to compress and the valve plate to rise, and the fuel is ejected through the metering hole. When the fuel injection pulse output by the ECU ends, the valve plate is reset under the action of the spring force.
Fuel Injector Working Principle
The fuel injector is installed on the cylinder head near the intake manifold or the intake port through the seal ring, and the electromagnetic coil is connected according to the fuel injection pulse signal sent by the ECU. Under the action of the magnetic field of the electromagnetic coil, the needle valve overcomes the spring force. Raise and inject fuel into the intake manifold or manifold. When the ECU turns off the fuel injector, the injection is stopped. When the structure of the fuel injector and the fuel injection pressure are fixed, the fuel injection quantity of the fuel injector depends on the opening time of the needle valve, that is, the energizing time of the electromagnetic coil.
Drive mode of the fuel injector
The drive mode of the fuel injector can be divided into two types: current drive and voltage drive. Voltage drive is to drive the injector according to the voltage signal output by the ECU, and current drive is to drive according to the larger current output by the ECU. Current drive is only suitable for low resistance type injectors, voltage drive is suitable for both low resistance type injectors and high resistance type injectors.
Fuel Injector Control Circuit
The fuel injector has two terminals, of which terminal 1 is connected to the battery through the main relay, and terminal 2 is connected to terminal 17 of the engine ECU.
Maintenance of Fuel Injector
1. Check the injector online
When checking the fuel injector, the engine speed sensor should be normal, and the fuel pump relay (the fuel pump relay supplies power to the fuel injector) should also be normal.
① Remove the upper body of the intake pipe, remove the plug of the spark plug, remove the cover of the injector, and remove the plug from the injector.
② Connect the diode test pen to the 1-cylinder injector plug terminal with an auxiliary lead, and start the engine. The light-emitting diode must flash. Repeat the above test on the 2 to 4-cylinder injector plug.
③ If the diode of each cylinder is off, connect the diode test pen between the injector terminal of 1 cylinder and the ground.
④ When starting the engine, the LED must flash. If the diode does not flash, check the wire between the 2-hole plug terminal of the fuel injector and the fuel pump relay for a break point according to the circuit diagram.
⑤ If the diode does not flash on one or more cylinders, check the wires between the injector plug terminals for open circuits and short circuits with each other according to the circuit diagram.
⑥ Check the fuel injector resistance between the contacts. The specified value of the fuel injector resistance is 13 ~ 18Ω (high resistance type), and the resistance is increased by 4 ~ 6Ω when the engine is hot, otherwise the fuel injector should be replaced.
2. Check the resistance of the fuel injector
When faults such as blockage and drip occur in the fuel injector, the engine ECU cannot detect it, nor can the fault information of the fuel injector be read using the fault reader. The maintenance injector can be judged by detecting its resistance and voltage.
Use a multimeter OHM × 200Ω or R × 1Ω to detect the resistance of the injector solenoid. When testing, unplug the two-terminal harness connector on each injector, and check the standard resistance of the electromagnetic coil between the two terminals on the injector socket, which should meet the requirements in the following table. If the resistance value is infinite, it means that the electromagnetic coil is broken, and the fuel injector should be replaced.
3. Check the voltage of the electromagnetic injector
Injector power supply voltage can be detected with digital or pointer multimeters. When testing, unplug the two terminal plugs on each injector respectively, turn on the ignition switch, and the engine will not start. Detect the voltage between the two terminals on the plug and the engine block. The power supply voltage is the vehicle power supply voltage), the low level is
zero. If the voltages are all zero, it means that the power circuit is not working, and the fuel pump relay and fuel injection fuse should be repaired.
4. Detect the control pulse of electromagnetic injector
When detecting the injection pulse voltage of the injector, unplug the injector harness plug respectively, and connect two light-emitting diodes in series between the two terminals of the plug (two diodes in parallel, and the anode of one diode is connected to the other diode Negative) and a 510Ω / 0.25W resistor (resistor and diode in series) composed of codec. When starting the engine, the LED should flash. If the diode does not flash or emit light, it indicates that the injector power supply circuit, fuel pump relay or control ECU is faulty. Replace the ECU if necessary.
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