Don’t Ignore These Warning Signs of a Blocked Fuel Injector!

(Last Updated On: March 1, 2024)

A car cannot run without fuel injectors, so it highlights their importance and that they are always working correctly. The bad news is they can become clogged over time, causing various drivability issues. A rough-running engine, which feels like a vibration, is the most common symptom of a blocked fuel injector. Among the many causes of a blocked injector, running extremely low on gas is the one I see the most. When the fuel level drops, all the sediment and contaminants at the bottom of the gas tank swirl and get drawn into the engine, blocking the injector.

In this article, I have explained this, along with other symptoms, causes, and ways to cure and prevent this issue from happening.

How Fuel Injectors Work

Fuel injectors spray fuel into the engine cylinder (combustion chamber) at high pressure, in fine mist and a specific pattern. This process ensures that the fuel is burned efficiently, which maximizes power output and minimizes emissions. The engine’s computer (ECU) controls the fuel injectors, which use information from various sensors to determine the amount of fuel to be injected.

When the engine is running, the fuel injectors open and close rapidly, injecting fuel at the appropriate times to ensure optimal engine performance.

Symptoms of a Blocked Fuel Injector

If one or more fuel injectors in your vehicle become clogged or partially blocked, they won’t be able to deliver the necessary fuel at the correct time or in the right quantity. This will cause some noticeable symptoms, which include:

  • Engine running rough – With a blocked injector, the engine may misfire, hesitate when accelerating, or run lumpy.
  • Reduced fuel efficiency – A blocked fuel injector will cause the ECU to detect, via one of the sensors, a problem. It will try to counteract the problem by injecting more fuel, increasing fuel consumption.
  • Failed emissions test – Because the engine is burning fuel inefficiently, it will cause an increase in emissions. If you took your car for an emissions test, a failed test might be the only indication of a blocked injector, especially in the early stages. 
  • Check engine light – Once the ECU detects the engine is not injecting fuel optimally and thus not burning it right, the check engine light will illuminate. 
  • Strong smell – A blocked fuel injector may cause fuel to leak into the engine, leading to a strong fuel smell and a fire risk if fuel drips onto a hot engine part.
  • Engine vibration – If the fuel injector is partially blocked or the spray pattern is wrong, it can cause the engine to vibrate or shake. This will get worse the faster you drive. 
  • Engine Stalling -In severe cases, especially when multiple fuel injectors are blocked, the engine starves as it cannot receive enough fuel, often leading to the engine stalling when idling. 

What Causes a Fuel Injector to Get Blocked?

One of the most common causes of blocked fuel injectors is the buildup of dirt and debris in the gas tank. This occurs as impurities settle at the bottom of the fuel tank or when air and moisture enter the system over time. When you drive very low on fuel, these impurities get picked up and pumped into the fuel injectors, causing a buildup. This buildup prevents the injectors from spraying fuel correctly.

Another reason fuel injectors can become blocked is the use of low-quality fuel or fuel that contains high impurities. Low-quality fuel can contain contaminants that cause deposits to form inside the injector, leading to blockages. This issue typically develops over time and can be attributed to normal wear and tear, especially in older engines with higher mileage.

In addition to the impurities and debris in the bottoms of the gas tank, the fuel filter removes these before they enter the engine. However, if the fuel filter is not changed at regular service intervals or if it just gets clogged, the debris will force its way through the filer, causing the injector to get clogged.

clearing a clogged injector

Can You Drive With a Bad Fuel Injector?

If the car is badly misfiring or you can smell gas leaking due to a blocked injector, don’t drive it. There is a potential fire risk, and you will cause damage to engine internals. The injector may need to be ultrasonically cleaned or replaced; more information on this later. If you ignore this, the blocked injector will eventually get so bad that the car won’t start. 

However, if the injector is partially blocked, you may feel this as the engine is running a bit rough or lumpy. In this case, there is a method to unblocking it, which involves driving the car. 

Unblocking a Clogged Fuel Injector

If you suspect a fuel injector is only partially clogged, then using a fuel injector cleaner is a simple way to clear the blockage. You can find these at auto parts stores, and they require no prior experience to use. Simply pour the fuel treatment into the gas tank and drive. They are designed to break down and dissolve any deposits building up on the injectors.  

Another option is to manually clean the injectors; this often works when the fuel injector is completely blocked. It involves removing them from the engine and sending them away to be ultrasonically cleaned with a specialized tool and cleaning solution. This service can be costly, but replacing the injectors can be cheaper. If none of these methods work, the problematic fuel injector(s) must be replaced.

How To Prevent A Fuel Injector From Blocking 

Regularly using a fuel injector cleaner is one way to prevent a fuel injector from blocking. This will prevent any buildup from forming on the injector. However, please make sure to read the bottle on recommended usage. Overusing fuel treatments can have the opposite effect, causing damage to other engine components. 

It’s also important to use high-quality fuels from trusted gas stations. Additionally, avoiding letting your fuel level get too low can help prevent sediment from rising from the bottom of the tank and entering the fuel lines, causing blockages.

Frequently Asked Questions

Is It OK To Replace Just One Fuel Injector?

Replacing all fuel injectors at once is recommended to avoid an imbalance in the system. However, if you need to replace just one injector, it is possible, but you must make sure to have the others tested or cleaned. 

Can A Bad Fuel Injector Damage The Engine?

When a fuel injector is blocked, it can lead to an uneven fuel distribution, which can cause engine misfires, rough idling, and a decrease in fuel efficiency. Over time, this will damage the engine’s internals and the catalytic converter.

Final Thoughts

If you have a blocked or partially blocked fuel injector, it can cause your engine not to run properly. You may feel misfires, see the engine management light turn on, and smell gas. The severity of the issue can vary, but one solution to fixing a blocked injector is using a fuel injector cleaning treatment. It’s also an excellent preventative measure to use these treatments occasionally. If a fuel treatment doesn’t work, you will likely need to replace the problematic injectors, which I strongly recommend is carried out by a mechanic. 

My name is Tom although my friends call me Tommy. Messing around with cars and bikes has always been a hobby of mine even from a young age. So I made it my day job 17 years ago. I am a fully qualified mechanic as you would expect. I've worked in all different areas of the motor trade, valeting, panel beating, engine repairs, I'm sure you get the idea. I enjoy sharing my wealth of knowledge and experience with others, which is the reason I spend a lot of time here writing for this website.

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