How a gasoline injector works - Electric circuit

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In this article I explain how an injector works electrically. With diagrams, circuits and images, very easy to understand.

How a gasoline injector works - Electric circuit

How about, my friends, here is a small but very good summary of how the computer operates the electrical part of a gasoline injector. It seems incredible that there is not any information about it on the internet, so I'm going to put a small bit with this article.

What is the injector

In general, a gasoline injector is nothing more than a needle valve operated by a solenoid, so when the coil is energized, it attracts the rod that opens the needle and lets the fuel pass through. When the solenoid current is removed, the internal spring, aided by the pressure of the combustible fluid, moves the water to its closed position.

Ok, then, to summarize accounts we already know that to be able to open an injector we need to energize it with 12V. This will leave open until we remove the supply voltage. Simple.

The inductance of a normal injector is approximately 8.5mH. Of course, the resistance of the winding must be added, which is approximately 15 ohms.

How does the computer run the injectors?

First, let's look at this small general electrical schematic for connecting injectors. For this case I did it for two injectors, but it's the same for more injectors.

circuito electrico de inyeccion

As you can see in the previous image, the positive feed reaches all the injectors without interruption, in case it does not happen with the negative that if it has a suiche. Why interrupt the negative part and not the positive part? Basically, it is because the transistor is made with transistors, and the negative transistors are more economical than the positive transistors.

 Now that we have seen the scheme, to simplify a bit, we replace everything with its electrical symbols. This is shown in the following figure.

Circuito de activación de un inyector

The suiche is a transistor (Q1) usually placed in the Darlington configuration, which upon receiving the activation signal becomes saturated and opens the current path to earth. In this case, open the injector (L1).

 For older computers (1997-2006), integrated circuits were used that grouped a set of 4 Darlington to handle 4 injector outputs in the simplest configuration shown below:


circuito transistorizado activador inyector

By then the benefits of encapsulating the 4 outputs in an IC were used just to save space and better dissipate the heat generated. Even, the auxiliary elements of protection, rarely went inside this integrated circuit. As it is the Zener diode Z1 that protects the electronic system from the peaks of the coil of the injector and the Rs which is the resistance that limits the current of the injector.

Now, everything looks simple, does not it? But the problem with this configuration is that it consumes a lot of energy that must be dissipated by the transistor to the metal housing of the computer and that good ... decreases the useful life of the transistor and its associated components. To solve this problem the engineers modified the previous circuit a bit and added a handler.

The circuit is more or less the following:

Circuito de activación de un inyector

Practically everything left as it was, only now added an integrated circuit that acts as a handler of the power stage that energizes the injector.

Injector driver.

To not complicate matters, the driver basically does that, when receiving the signal to open from the CPU control module, it puts the transistor in full saturation so that the injector consumes the maximum current required to overcome the kinetic forces and of constriction that allow its opening. After this process, the circuit goes into retention state, where the transistor is placed to work so that it only allows 1/4 of the maximum current to remain open until the CPU's opening signal disappears. when the handler cuts the transistor and in this way the injector is turned off.

In this way the energy consumption of the system is reduced in addition to lowering the operating temperature of the other associated elements.

Additionally, in recent years, greater functionality has been added to the injector driver, placing an operation detector made up of two voltage buyers. What these elements do is tell the CPU of the car computer if the injector is present, and if there is a short one in it.

If faults are detected, the CPU automatically stops sending the Open / Close signal of the injector and makes corrections. And if ... the CHECK ENGINE will appear on the board. Hahaha.

forma de onda de activación de un inyector

In the previous image you can see the characteristic waveform formed in the control terminal of the injector. Practically the image is self-explanatory. At the start of the activation pulse, the terminal has 12V coming from the battery (which arrives there by the resistance of the injector), at that moment the voltage goes practically to zero because the transistor starts to drive the current of the injector. Here occurs the current peak that the handler allows to pass for a few milliseconds for the injector to open, after that time it is placed in hold mode, and the current drops to 1/4 of the maximum current required.

 A commercial driver very common in computers is the Texas Instruments LM1949 and the TPIC46L02

 Test the injectors

How to test if there are pulses of injector

click here to go

How to make a nozzle tester

Click here to go


Table of standard values of resistance of injectors

Table of resistances:

Injector cold: 22 ºC y 50ºC

11 – 16 ohm

Injector hot: más de 50ºC

20 – 26 ohm

So that the reader is not confused, the injector is a coil and when it is in operation it works as such and opposes the current changes. So these values should not be taken to perform electrical calculations by ohms law since they will be incorrect.

They are only referential to measure the resistance of the coil. Do not confuse resistance, with coil impedance.

Do you want to make a homemade nozzle tester?

Here in this article of the link you can see how to make it easily at home.

how to make a homemade nozzle tester

Do you have questions or doubts?

Questions or suggestions can use the form below and I will gladly answer them.

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Written by Dennis García.

Chica Mecánica



Muy completa la informacion.

Tiene hasta el circuito de control. Excelete Dennis.


    Muy buen articulo

    Excelente Dennis.

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      How a gasoline injector works - Electric circuit

      How a gasoline injector works - Electric circuit

      In this article I explain how an injector works electrically. With diagrams, circuits and images, very easy to understand.

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      • Asked by Maria
        on 03/12/2019
        Excelente información Dennis, es posible usar un L293 para controlar los inyectores? es para un banco de simulación. Answer:
        Claro Maria, pero debes colocarlo algo separado de la placa para que disipe bien el calor y el tren de pulsos debe ser corto, como de 40ms, maximo unos 70ms, para evitar el calentamiento del circuito l293. Pero es una excelente idea.
      • Asked by bautista lovera
        on 08/08/2019
        Tengo un WW bora año 2002 y no le llega corriente a los inyectores, he revisado los fusibles y estan bien, me podria orientar un poco, gracias Answer:
        Bautista, Para ese caso te dejo un video que yo hice de como es el procedimiento para revisar la parte electrica de pulsos de los inyectores.

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