HomeHow It WorksSpotting Trouble: The 5 Symptoms of a Bad Fuel Injector

Spotting Trouble: The 5 Symptoms of a Bad Fuel Injector

With so many systems on modern cars it is hard to know where to start when your vehicle starts to have issues. Let’s take a closer look at some of the most common symptoms of a bad fuel injector. 

How do I know if I have a bad fuel injector?

Correctly working fuel injectors are crucial for the efficiency and performance of your vehicle’s engine. However, over time these problems can lead to a range of issues that affect performance and fuel economy.

Identifying the symptoms early is the key to preventing costly repairs and damage. WE are going to explore the common symptoms of a bad fuel injector and how you can identify them.

With this information you will have the knowledge to diagnose fuel injector issues and take action.

A table showing causes of symptoms of a bad fuel injector

CEL (check engine light) is illuminated

If a vehicle has a bad fuel injector the most common issue that you will notice is the check engine light illuminated on the dash. The PCM (Powertrain Control Module) or engine computer has the ability to do self diagnostics on all engine systems. 

This self diagnosis will run multiple different tests as you are driving down the road. If it detects an issue with a fuel injector it will confirm that there is a problem and set a code if necessary. 

You will need a code reader to check to see if the problem is related to a faulty fuel injector. Bad fuel injector codes will generally be P0300-P0312, these codes set when there is an individual cylinder misfire. 

The cause of this code could be ignition, mechanical, or fuel related. Because of the many causes of this code ensure that you are careful in your diagnosis or take it to a knowledgeable technician for repair.

Check engine light a symptom of a bad fuel injector

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 common symptom of a bad fuel injector is engine misfires and poor engine performance.

A fuel injector that is clogged can cause your 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 fuel injector pintle and seat it can inject fuel into the cylinder at all times. This excessive amount of fuel in the cylinder will cause the vehicle to begin to smoke heavily.

The color of the smoke from a bad fuel injector on a gasoline engine is black smoke. This black smoke is caused by 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 smoke 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 of your vehicle when you fill up. Don’t worry, this is not very hard today.  There are many apps that make it as simple as a few taps of the screen.

As a vehicle owner the best reason to keep track of this data is to know when there is a decrease in your fuel mileage. This will help you identify an issue quickly before it gets worse and help increase your fuel mileage.

As you can see above there are many symptoms of a bad fuel injector. The reasons that we have discussed above are failures of the mechanical components of the injector. The fuel screen may have become clogged with sediment or possibly 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.

A fuel rail showing a bad fuel injector and good fuel injectors

Failed Tailpipe Test

This is a very common symptom of a bad fuel injector. Depending on the area that you live in the country, you may be required to have a tailpipe or emissions test done once per year. This test is important in maintaining our air quality. 

By placing a “sniffer” probe into the tailpipe, a computer is able to determine the emissions that the vehicle is producing.

If you have a faulty fuel injector the tailpipe test will most likely fail. The fuel injector will not provide the correct air/fuel mixture to the cylinder resulting in poor or incomplete combustion. 

This simply means the fuel in the cylinder is not being used correctly. This creates excessive emissions which can cause you to fail the test.

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 what fuel injectors cleaners are trying to do. As we discussed above there are two forms of failure in a fuel injector, electrical or mechanical.

At the top of the fuel injector where fuel enters 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 allow the fuel injector to finely atomize the fuel spray. Because they are small they can also become clogged by dirt and debris or by varnished fuel. 

When this build up occurs it blocks the flow of fuel through the injector and does not supply enough fuel to the cylinder to fire correctly.

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 used professionally at your local auto mechanic is a concentrated version. The fuel injector cleaner is used to feed the fuel rail of the vehicle directly, taking the place of the gasoline that would normally be supplied to the fuel rail. The engine is then run for a period of time 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 I mentioned earlier, 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 best to use fuel injector cleaner as part of your vehicle’s proper preventative maintenance plan. Manufacturers recommend using fuel injector cleaner every 3000-5000 miles or as per the instructions on the bottle. Personally, to make it easier to remember, every oil change is a great interval.

This will make sure 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?

To replace a fuel injector the cost can range from $30 on a standard sequential port fuel injected vehicle to over $1000 on a vehicle that is direct injected. 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.

Tester for testing bad fuel injectors.

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 first mailed to a rebuild facility. The rebuild facility checks the integrity of the fuel injector to see if there are any issues that prevent the rebuild process. Once 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 and can also be 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 you 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 www.toptiergas.com 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.

There are many reasons that cause symptoms of a bad fuel injector. Hopefully you have learned a little bit more about about how to identify the issues that your vehicle has.

John Morris
John Morrishttps://autoknowit.com
John Morris is the technical editor for AutoKnowIt.com. His years of experience in automotive repair as well as an automotive professor have prepared him to ensure that even the most technical information is accurate and concise at all times.

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