How do fuel injector systems in cars work? Revealed!


Posted by: Joshua-Philip Okeafor

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Without the silent workings of fuel injector systems in cars, vehicles would not move at all. Find out all the details of how it works. Read now!

For fuel efficiency and smooth operation, the internal combustion engine needs the right quantity of fuel/air mixture according to its demands. What then is the purpose of the fuel injection system and how do fuel injector systems in cars work?


A fuel injector might be small but mighty

What are fuel injectors?

What really are fuel injectors? The fuel injector function is to deliver fuel to the engine cylinders while accurately controlling injection timing, fuel atomization as well as other parameters.

What are the fuel injector types?

They include:

  • Pump-line-nozzle
  • Common rail
  • Unit injector

Fuel injector working principle with Petrol-engine vehicles

Car engines, which are powered by petrol, use what is called the indirect fuel injection. The fuel pump sends the petrol to the engine bay, which is then injected into the inlet via an injector. There are two ways to this. It’s either each cylinder has separate injectors, or one or two injectors running into the inlet manifold.

There has been debate about which is better, carburetor, or injector? Traditionally, the carburetor, which is not perfect, controls the fuel/air mixture. What keeps it at a disadvantage is the fact that just one carburetor cannot successfully supply a four-cylinder engine the necessary fuel/air mixture needed at any time because of the distance between the cylinders and the carburetor. The solution to this is to use twin-carburetors which are difficult to correctly place in sync. Thus carburetion is not so efficient.

To solve the entire problem, fuel-injected engines were fitted in cars, making it easy for fuel to be delivered precisely in bursts. These engines are well equipped to be powerful and efficient as compared to the carbureted ones. They also prove to be more economical and have less poisonous emissions.


A fuel injector system looks complex but is really easy to understand, right?

Fuel injector working principle with Diesel-engine vehicles

While petrol-engine cars use the indirect fuel-injection system, the diesel engines use direct injection where the diesel is injected straight into the cylinder that is filled up with compressed air. There are some diesel engines that use indirect injection where the diesel fuel is injected right into the combustion chamber. This is specially shaped in a way that it has a narrow passage that connects it to the cylinder head.

The air, that later self-ignites, is drawn to the cylinder and heated by compression in a way that the atomized fuel is injected at the extreme of the compression stroke. The fuel injector oil in the crankcase of an engine that uses direct fuel injection makes a big difference in the health of an engine. Using the right oil reduces deposits of carbon on the intake valves as well as makes the engine very healthy.

How fuel injectors work

All modern petrol injection systems use the indirect form of injection. The fuel injector pump sends pressurized fuel through the fuel tank to the engine bay where it is then distributed evenly to each cylinder while still under pressure. While systems vary, the fuel is either fired through the inlet port or manifold through an injector.


A leaking seal is a common problem

What a fuel injector nozzle does

This works like the spray nozzle of a hose which ensures fuel comes out like a fine mist. Here, the fuel mixes with that air going through the inlet port or manifold after which the fuel/air mixture enters the combustion chamber. Some complex cars with multi-point fuel injection feed each cylinder via its own fuel injector pump which makes the process expensive.

It is, however, very common to have a single-point injection where just one fuel injector pump feeds all the cylinders or having one fuel injector pump feed every two cylinders. The fuel rail, the injectors, and also the intake manifold are individual components so they need a seal when they are assembled and fastened together. These fuel injector seals are made of polyurethane or nitrile rubber because of their fuel resistant properties. All parts of the fuel injector work together to form a fuel injector kit.

These much talked about injectors through which fuel is sprayed are first capped with a nozzle and screwed into the cylinder head or inlet manifold then angled so that fuel spray is targeted towards the inlet valve. These fuel injector types depend a lot on what the injection system is. The first system makes use of continuous injection with fuel squirted into the inlet port during the engine running times.

The injector then acts as a spray nozzle to break fuel up into a fine spray (not controlling fuel flow). The mechanical or electrical control unit is responsible for decreasing or increasing fuel spray which is like turning a tap off or on. The second system is called the timed injection or pulsed injection. In this system, the fuel gets delivered in bursts to correspond with the induction stroke of that cylinder. Just like for the continuous injection, a timed injection could be controlled electrically or mechanically.

How other parts of the injector system work

Let’s take a look at some other aspects of the injector systems and how they work

  • Because there is an interconnected system linking the filter, fuel pump, and fuel injectors, these  fuel injector parts might get clogged up with dirt and debris. A fuel injector cleaner and fuel injector flow testing may be required to clean the dirt, debris and build up out of our fuel injection system. Once your fuel system is clogged, it can cause damage to other engine parts and can lower the overall performance of a car, its fuel economy, and even a total engine shutdown.

The best thing is to make a routine of fuel injector cleaning and fuel injector flow testing from time to time.     

  • The fuel injector filter screens out dirt, rust particles, and debris from entering the engine or fuel injection system and causing it damage.
  • Fuel injector lubricants come from the fuel. When the valve closes, fuel is kept around the injector’s pressure side where it will not be evaporated neither will it dry out. The little gasoline performs as a lubricant when it passes over the valve’s plunger and gets injected right into the compression chamber.  However, gasoline fuel injectors don’t need the kind of lubrication that a diesel fuel injector does.
  • The fuel injector flow calculator calculates and tells you what size of fuel injectors you will need. What you just need to do is just input simple details into it and you get it. The explanations of each input are found below the calculator.


Cleaning the injector can be done easily if you know how to

Fuel injector problems

How do you detect fuel injector problems? Some of these fuel injector leak or damage or fuel injector symptoms are noticed:

  • Increased fuel consumption
  • Poor emissions
  • Rough idle
  • Problems starting when the engine is still hot and many more


Fuel injector could go bad and stop functioning well

These fuel injector issues need to be settled at once for the car engine to keep going. Drivers must understand how fuel injector pressure works and how it is applied. Knowing what to expect from the fuel pressure makes you able to diagnose any problem with the fuel system. This helps the vehicle function as you intend it to. Fuel injection pressures during every healthy process must be above 1000-1200 bar for good spray formation as well as air-fuel mixture. There is a possibility to attain up to 1600-1800 bar.

Watch a fuel injection system working live:

Electronic Fuel Injection System Working


Though some parts of this needed to be a bit tech, hopefully, you now know the answer to the question: how do fuel injector systems in cars work? You can also stop asking: What really are fuel injectors? Also, remember to do your regular fuel injector testing using these simple fuel injector testing tips. This is to catch fuel injector leak symptoms in time.

>>> Only the most informative maintenance tips here.

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Joshua-Philip Okeafor

Joshua-Philip Okeafor

Car buying & selling

Joshua, or KK as friends call him, is a Filmmaker, Writer and Director. A Christian, Joshua is a product of Nigeria’s foremost film school, the National Film Institute, Jos, where he majored in Writing/Directing. Joshua began his writing career at age 18 when an older brother gave him a four page outline of a children novel. Joshua intends to keep writing and directing. His screen name is sometimes Joshua Kalu Ephraim (Writing), and sometimes Joshua KK (directing).

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