The Ultimate Guide to Fuel Injectors (2022)

Believe it or not. Magic is not what makes fuel injectors work. Read on to learn more about everything you ever wanted to know about fuel injectors.

With modern technology making its way into even the smallest of engines we are seeing fuel injectors equipped on engines from the smallest lawn mowers up to the largest dually pick up trucks you see travelling up and down the highways. So, lets jump in and learn more about this indispensable component that completes such a large role for the automotive engine.

The fuel system on a vehicle needs to do 3 things correctly to ensure that the vehicle will run correctly while producing the most amount of power with the least amount of fuel and emissions. The fuel system needs to inject fuel at the right time, in the right amount, and for the correct time. These three things may seem small, but they are very important tasks to ensure that are engine is running the way it was designed.

How does a fuel injector work?

When we are discussing how a fuel injector works, we have to remember we are dealing with a small portion of the fuel injection system on a modern automobile. The fuel injection system begins with the fuel pump where a pump creates pressure and flow to force the fluid through the fuel lines. These fuel lines than feed the fuel rail with a constant supply of regulated and filtered flow to be delivered to the individual injector.

Once the fuel reaches the fuel injector it is already regulated, meaning the pressure is set by a fuel pressure regulator that adjusts for driving conditions and power requirements that the engine requires at that specific moment in time. The fuel injector is connected to the fuel rail as well as the intake manifold with 2 O-rings, one located on the fuel rail the other to seal the connection between the intake. We need to ensure these areas are sealed to prevent unmetered and unfiltered air from entering the engine.

The fuel injector itself is a small work of technical wonderment, it is complicated but let’s take you through step by step to let you completely understand what is going on. Please refer to the image to help your understanding, how does a fuel injector work.

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This is an image of a port fuel injector. The many components are shown in the image to help you identify the components as we begin to understand how the injector works.

Step 1: Before anything happens, we need to remember that fuel is supplied to the fuel injector. This means that clean pressurized fluid is at all times when the vehicle is cranking/running supplied to the filter at the top of the connector. This fuel is blocked from exiting the fuel injector by the needle pintle which is located at the bottom of the needle. This needle pintle along with the seat form a seal which prevents pressurized fuel from exiting the injector and being injected into the combustion chamber.

Step 2: The injectors basic function is with the use of what is called a solenoid. This electrically operated solenoid in the image is referred to as a coil. Effectively what this coil does is create a magnetic field when a power and ground are supplied to the coil. This magnetic field causes movement of the needle.

Step 3: At the correct moment that the PCM determines it will provide a power and ground to the injector. This will cause the coil to magnetize. This magnetic field will than draw the needle upward lifting the needle pintle from the seat.

Step 4: The movement of the needle pintle from the seat provides an area for the fuel to exit from the injector. This pressurized fluid travels through the seat and through the orifice disc.

Step 5: The orifice disc does the important job of turning the fuel into a highly atomized spray. The fuel needs to be atomized to ensure proper combustion when the air/fuel mixture is ignited.

Step 6: PCM turns off the injector by opening the circuit, this causes the magnetic field in the injector to collapse. The needle pintle will than be forced downward by spring pressure to seal the pintle and seat before the next injection sequence begins.

Step 7: This task is completed in 1-10 mS depending on engine load and design of the injector. While the engine is at 2500 RPM this task is completed 1250 times per minute for each injector that the vehicle is equipped with.

Pretty amazing stats above aren’t they. Sometimes forgotten heroes of the modern automotive engine. As you can imagine with all of the opening and closing sequences that occur with the modern-day injector problems will arise.

How do I know if I have a bad injector?

CEL (check engine light) is illuminated

The most common issue that vehicle owners will notice is the check engine light illuminated if the fuel injectors have an issue. The PCM (Powertrain Control Module) or engine computer has the ability to do self diagnostics. This self diagnosis will ensure the electrically the fuel injectors are functioning properly, but it also has the ability to determine if the fuel injectors are functioning mechanically as well.

Once you check the codes with a code reader, codes related to fuel injectors will generally be P0300-P0312. These show faults with individual cylinder misfires, the cause of this code could be ignition/mechanical, or fuel related. Because of many causes of this code ensure that you are carful in your diagnosis or take it to a knowledgeable technician for repair.

Poor engine performance/misfires

If your vehicle is not equipped with OBD 2 or possibly you have a custom “LS” swapped vehicle that has an aftermarket fuel injection system, another symptom of a bad fuel injector can be engine misfires or poor engine performance.

A fuel injector that is clogged can cause the vehicle to have multiple symptoms. First, if the injector is partially clogged you could notice the vehicle does not perform like it used to. Take, for example, merging onto the busy freeway. When you push the gas pedal to the floor your vehicle does not seem to accelerate like it used to.

This lack of power could also be combined with an engine misfire. Does the engine vibrate more than usual when you are stopped at a stop sign? This could be a sign that the cylinder is misfiring from a bad fuel injector.

Black Smoke from tailpipe

If the fuel injector does not properly seal between the pintle and seat it can inject fuel continuously into the cylinder. This excessive amount of fuel in the cylinder will cause the vehicle to begin to smoke heavily.

The color of the smoke that informs us of a bad fuel injector on a gasoline engine is black smoke. This black smoke is due to unburned fuel being released from the tailpipe of the vehicle.

A good example of this would be a diesel vehicle that competes in truck/tractor pull competitions. The black fuel that is coming out of the exhaust system is raw unburned fuel. Not very good for the environment or fuel economy if you ask me.

Poor fuel economy

Another symptom of a bad fuel injector is poor fuel economy. It is always a good idea to track fuel mileage continually when you own a vehicle. There are many apps today that make it very simple to be able to do this.

An advantage of tracking this vital information of our vehicle is as an owner you can track when fuel economy decreases. A bad fuel injector may not allow enough fuel or provide too much fuel into the cylinder which results in incomplete combustion.

Due to this incomplete combustion the engine is not working at its designed capacity and its fuel economy may suffer.

As we see above there are many symptoms of a bad fuel injector. Most of the reasons that we have discussed above are generally failures with the mechanical components of the injector. The fuel screen may have become plugged with sediment or possible there is dirt trapped between the pintle and seat holding the injector open when it should be closed.

These issues can sometimes be solved with using fuel injector cleaner on a regular basis.

How do fuel injector cleaners work?

Fuel injector cleaners come in two main different types, consumer use and professional use.

Before we continue, we need to understand when fuel injectors cleaners are trying to do. As we discussed above there are generally two forms of mechanical failure in a fuel injector, there are also electrical failures but that is better suited to an electrical diagnosis article. If you refer to the above image of the fuel injector at the top, there is a filter. This filter is present to ensure that any sediment or foreign material is filtered before reaching the injector.

The injector nozzle consists of many small holes, these holes give the ability for the fuel injector to finely atomize the fuel spray. They can also become clogged if sediment is allowed to travel through the injector.

Over time this filter can become clogged with sediment or other types of foreign material. Once this happens it blocks the flow of fuel through the injector and does not supply enough fuel to the cylinder to fire correctly.

The other method of failure is a piece of foreign material or varnish build up on the pintle and seat. As we discussed earlier in this guide the pintle and seat seal to prevent fuel from entering the combustion chamber. Anything that prevents this seal will cause fuel to flow into the cylinder when it is not appropriate, possibly causing a misfire or smoking condition.

Fuel injector cleaners try to combat this build up of varnish and foreign material by breaking down this build up. There are two different ways fuel injector cleaner may be used.

Consumer use fuel injector cleaners consist of a fuel injector cleaner that can be poured into the gas tank. Once it makes its way into the fuel tank it mixes with the fuel, when the fuel is circulated through the fuel system the cleaner makes its way to the fuel injector to complete the cleaning process.

The commercial version, which is used professionally at your local auto mechanic is a more concentrated version. This fuel injector cleaner is generally running directly to the fuel rail of your vehicle, taking place of the fuel that would normally be supplied to the fuel rail. The engine is than ran for a time period until all of the injector cleaner has been run through the injectors.

Even though the delivery methods are slightly different the end result is the same. The only downfall of fuel injector cleaners is if you have already noticed an issue, you probably are too late for fuel injector cleaner to work.

Remember that filter, if we break down that sediment with a solvent that sediment has to travel through the injector before it is injected into the cylinder. Possibly causing another issue with the fuel injector tip clogging.

How often should fuel injector cleaner be used?

As we found out above, it is better to use fuel injector cleaner as part of your vehicle’s proper preventative maintenance plan. Most manufacturers recommend using fuel injector cleaner every 3-5000 miles as per instructions on the bottle. Personally, to make it easier to remember, every oil change is a great interval.

This will ensure that no varnish or other types of materials will build up in your fuel system, possibly leaving you stranded.

Sometimes you are going to run into an issue that your fuel injector is faulty, and you need to replace a fuel injector.

How much does it cost to get a fuel injector replaced?

A fuel injectors cost can range from $30 on a standard sequential port fuel injected vehicle to over $1000 on a vehicle that is direct injected. Also depending on the type of fuel system that the vehicle is equipped with you may be looking at removal of engine components to gain access to the components and replacement of certain fuel lines, etc.

Are there alternatives to replacing fuel injectors?

If you are in the situation where your vehicle needs a fuel injector replaced but the cost to replace is significant, there is an alternative – Rebuilding. Now rebuilding in the automotive industry is very common however there are not many people that realize fuel injector rebuilding is possible.

The process is fairly simple, the injectors are generally mailed to a rebuild facility. The rebuild facility checks the integrity of the fuel injector. Once this is completed, they remove the filters and run the injectors through a cleaner that flushes the injectors with a specialized cleaner.

Once the injectors have been cleaned, new filters are installed, and the injectors are flow tested. This means the amount of fuel over a specified period of time is checked to ensure that it fits factory tolerances. If all checks out, the fuel injectors are mailed back with a new set of o rings.

This is a great cost-effective option when it comes to replacing fuel injectors, also a great option for older or rare vehicles where parts are becoming harder and harder to find.

Replacing fuel injectors can be a large investment depending on your vehicle but with a little bit of knowledge of how this vital engine component works and how to maintain it correctly will have your vehicle running better for years to come.

How can I prevent fuel injector failure?

Fuel, Fuel, Fuel!

This is a very understated issue that is not always talked about in the industry. We are not talking about octane rating but the fuel quality.

Most people are not aware of what a Top Tier fuel is. Top Tier fuels were created in 2004 when leading manufacturers requested a fuel that had a greater level of additives which would give them a greater level of fuel performance when used in their engines.

To become a Top Tier fuel, fuels are required to have higher additive levels that provide greater deposit control performance.

Check out to learn more about where Top Tier fuel is available in your area. You will be surprised; you may have been using it all along.

Combine using a good quality fuel with regular injector cleaning and your injectors should continue injecting fuel for thousands of miles and years to come.

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