How to Check and Correct the Injection Pressure of the Car Injector?

by MOU YONG HONG on December 01, 2021

Some of the fuel injection pressure of the fuel injector can be adjusted (mechanical fuel injector), and some fuel injection pressure can not be adjusted (solenoid valve fuel injector), it depends on the type. For the pressure adjustment of the mechanical injector, the pressure of the injector needs to be tested first, and the adjustment is made if the pressure is not in the proper range.

Solenoid valve injector

Solenoid valve injectors are used in electronically controlled engines, including diesel engines and gasoline engines. This type of injector accurately controls the amount of fuel injected from the injection hole by receiving the fuel injection pulse signal from the engine ECU. The opening height of the nozzle hole of the oiler is fixed, and the ECU only needs to control the opening time of the valve.

The injectors used on EFI vehicles are solenoid valve type, which is an electronic device with a fine internal structure and high processing degree. It requires good dynamic response, strong anti-pollution and clogging ability, and the most important thing is the injection hole. The degree of atomization of the fuel sprayed from the oil is better.

The main internal component of this type of injector is the solenoid coil. The structure is as shown in the figure below. When the ECU is energized, the solenoid valve is energized to generate magnetic force to the armature, and then the needle valve is sucked up, and the fuel After being filtered by the filter, sprays out from the gap of the needle valve.

As can be seen from the figure below, fuel injectors are divided into pin type and ball valve type (hole type). Gasoline electronically controlled engines use porous type, generally 4-6 holes. Of course, it is not that the more holes, the better the atomization effect of the mixture. The more holes, the easier it is to block. If blocked, it needs to be cleaned and replaced. Therefore, it is not recommended that some car owners privately replace the original injectors. It is a porous fuel injection structure.

The fuel injection pressure of the electronically controlled fuel injector is adjusted by the oil pressure regulator, which cannot be adjusted by itself, and the pressure value adjusted by the oil pressure regulator is unchanged. The pressure difference between the oil pressure regulator and the intake pipe is maintained at 250-300KPa to maintain the pressure in the oil rail pipe. This pressure is also the pressure entering the fuel injector.

When the engine is working, the pressure of the diaphragm on the oil pressure regulator is the sum of the spring and the atmospheric pressure of the intake air. The pressure below is the pressure delivered from the oil pump. When the pressure is equal, the diaphragm does not move and maintains the pressure. Stable; if the pressure is unbalanced, adjust it through the elastic force of the spring, and the pressure adjustment curve is shown in the figure below.

Mechanical injector

Injector structure

The mechanical injector is used in the traditional diesel fuel supply system. The injector structure is shown in the figure below. We can see that the injector does not have a wiring harness connector. The side hole is the fuel inlet pipe connector. When the fuel enters from this hole, it is filtered through the gap filter element and enters the oil passage between the needle valve and the needle valve body. If the pressure is greater than the force of the upper pressure regulating spring, the needle valve opens and the diesel is sprayed from the needle valve, and the excess diesel flows from the return pipe to the fuel tank.

Injector inspection

The detection method of this type of injector needs the following 2 points:

1. Inspection and correction of fuel injection pressure: first place the fuel injector on the fuel injector pressure tester, as shown in the figure below, make sure that the fuel injector is firmly connected before testing, and it cannot appear when pressing the handle of the instrument There is a sound of air leakage, otherwise it means that the installation is not good and there is oil leakage. The injection pressure of the injector is based on the pressure on the gauge when the injector starts to inject. Normally, it is greater than 20MPa. If the opening pressure is less than this, it means that the injector is leaking and can be removed first. Open maintenance.

Then look at the holding pressure of the injector after fuel injection. The pressure should remain unchanged within 30 seconds, otherwise, the injector is broken. In the process of fuel injection by the fuel injector, it is also necessary to check whether the fuel injector can spray diesel fuel into atomized fuel jets under the specified pressure.

If the pressure of the injector does not meet the requirements, it will seriously affect the working conditions of the engine. The pressure of the mechanical injector is corrected by the tightness of the pressure adjusting screw, which can be seen by opening the pressure adjusting nut.

If the pressure is too low, the injection speed of the fuel injector will be slowed down, and the atomization cone angle will be reduced, making the diesel oil poorly atomized and causing leakage. At the same time, the amount of fuel injection will increase, the fuel injection time will be advanced, and the fuel injection time will be delayed, resulting in incomplete combustion, black exhaust smoke, and carbon deposits.

If the pressure is too high, it will cause a large amount of fuel injection pressure relief, shorten the injection time, accelerate the wear of parts, and increase the amount of fuel injection than usual, which also causes waste.

2. Detection of fuel injection advance angle: The fuel injection advance angle refers to the rotation angle of the crankshaft when the piston turns to the top dead center position when the injector opens the needle valve to inject fuel. The fuel injection advance angle is slower than the fuel supply advance angle, generally less than 8 degrees of crankshaft angle. The fuel injection advance angle is measured on the fuel injection pump test bench. If this equipment is not available, the fuel injection pressure of the fuel injector can be tested.

Summary: The correction of the injection pressure of the automobile injector is adjusted by the tightness of the pressure regulating screw on the injector. If the pressure does not meet the standard value, you can first carry out the decomposition and cleaning of the injector and look at the internal needle. Whether there are carbon deposits or wear on valves, oil passages, etc., if this is the case, it can only be repaired.


Please note, comments must be approved before they are published