10 Signs of a Dirty Fuel Injector and Replacement Cost

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symptoms of a bad fuel injector

Just two days before writing this article, I read the news that Mercedes-Benz AMG had to issue a recall in the U.S. The reason behind this recall was the leaking fuel into the passenger compartment. This leakage put the safety of passengers at risk.

When asked by the company why this leak had happened in the first place, they said it might have been due to problems in the production process. During which the fuel rail and fuel injectors “might not have been cleaned properly before assembly.”

This incident highlights the importance of clean fuel injectors.

What are Fuel Injectors?

signs of a dirty fuel injector

A fuel injector is at the head of the fuel delivery system in your vehicle. It controls and regulates the amount of fuel injected into the combustion chamber, producing combustion and power.

These days, you’ll hear the names of many fuel injection technologies. But primarily, they are of these two types:

1. The mechanically controlled fuel injectors 

2. The electronically controlled fuel injectors

The difference is evident in their names. They work upon different types of engine feedback, which is why they impact your engine’s performance and fuel efficiency differently.

Mechanically controlled fuel injectors receive information through a series of gears or other linkages. A certain amount of revolution or turning (tuned with the driver pressing the gas pedal) determines the amount of fuel flowing into the engine cylinder.

But this type of injector has become very rare. Electronically controlled fuel injectors are way more popular now. They offer better control over their functionality and enable massive cut downs on fuel consumption.

With rising fuel costs each day, EFI’s (Electronic fuel injectors) have become part and parcel of every modern-day vehicle.

How Does a Fuel Injector Work?

Fuel injectors carry out delivering the fuel into the combustion chamber. With the help of a small nozzle face and an electrically controlled mechanism, a fuel pump takes fuel from the tank, pressurizes it, and sends it to the injectors.

The fuel injectors spray fuel droplets into the intake manifold, where it mixes with air before entering the combustion chamber. The injectors atomize the fuel particle instead of spraying them in a jet stream. This process creates a thorough mixing of fuel particles and air.

The ECU of the car directly controls the fuel injectors. The sensors present in the fuel injector deicide the time and size of the opening.

Symptoms of a Bad Fuel Injector

fuel injector leak

Bad fuel injectors are impossible to ignore. The symptoms damage your vehicle, and most drivers recognize there’s a problem immediately. Here are the most common symptoms of problematic fuel injectors: 

  1. High Fuel Consumption
  2. Dirty Exhaust Emission
  3. Fuel Odor due to Leakage
  4. Misfiring in Combustion Chambers 
  5. Vibrating Engine 
  6. Fluttering RPM Needle
  7. Say Good-Bye to your Throttle Valves
  8. Engine Stalling
  9. Problems While Starting the Car
  10. Check Engine Warning Light 

Let us take a closer look at the bad injector symptoms:

1. High Fuel Consumption

leaking fuel injectors

The first and foremost symptom of a bad fuel injector is the decreased fuel mileage of your car. When the fuel injector is dirty or damaged, it will often spray more fuel than required.

A bad fuel injector will not determine the right amount of fuel required. The faulty decoding of signals might draw more pressurized fuel from the reservoir through the fuel pump.

This extra fuel goes to waste, which has separate repercussions. For now, if you notice a sudden increase in your car’s fuel consumption, then beware of the problems in fuel injectors.

2. Dirty Exhaust Emission

A bad fuel injector can even lead to dirty exhaust emissions. Each engine cycle ends at the exhaust stroke, where dirty gases produced are sent into the waste.

A bad fuel injector can cause a limited or abundant supply of fuel. In either case, the production of unwanted gases in the combustion process is enhanced. More dirty gases produced means more dirty emissions.

So, if you notice a clogged exhaust or failed catalytic converter, the root cause might be a dirty fuel injector.

3. Fuel Odor due to Leakage

As explained in the introduction, dirty fuel injectors can cause fuel leakage. When excess fuel is delivered into the fuel lines, there’s a chance that the extra fuel will find a hole or cavity to leak through. 

In the case of Mercedes-Benz, fuel was leaking from the seal between the fuel rail and the fuel injector. Fuel leakage is a serious issue that can lead to engine fires. The first thing you might notice in this case is the scent of gasoline. 

So, if you smell fuel inside your cabin or near the exterior of your car, then the fuel injector might not be working correctly.

4. Misfiring in Combustion Chambers

One of the most common symptoms of a faulty fuel injector is misfiring during combustion. The engine will misfire when there isn’t an adequate fuel supply, or a surplus of fuel is pushed into the combustion chambers.

Both these scenarios are possible with a bad fuel injector.

The amount of fuel being sprayed into the combustion chamber is adjusted to ignite at the end of the cycle only. In the case of an SI engine, spark plugs ignite the air-fuel mixture, and in the case of a CI engine, the mixture is compressed to the point of self-ignition.

Insufficient or abundant fuel might enable the ignition of the mixture before the desired location. This is called engine misfire.

5. Vibrating Engine

Unregulated levels of fuel can lead to vibration of the engine as well. When fuel injectors inject more or less fuel, the engine has to adjust its process according to that.

By this, I mean the dynamics of the engine cycle, not the cycle itself. The Otto cycle or Diesel cycle will be the same, but the working parameter might differ with the changing amounts of fuel.

Higher temperatures or pressure create specific vibrations. Hence, a bad fuel injector can cause your car’s engine to vibrate abnormally.

6. Fluttering RPM Needle

A bad fuel injector might show itself in the form of unstable engine rpm.

If you keep digging to the bottom of any symptom, you would know that it is due to faulty combustion. Even here, due to incomplete combustion, the power at the output shaft fluctuates since every rotation of the drive shaft is powered through the engine cycle.

Fluctuating power can result in the fluctuation of the RPM needle on your dashboard.

7. Say Good-Bye to your Throttle Valves

The throttle bodies and valves are built to withstand only a specific quantity of fuel. Excess fuel can lead to deposits around them.

A bad fuel injector can result in the delivery of excess fuel. Each type of fuel has specific contaminants that do not make their way to the combustion chamber. They are deposited on different components along the way.

Hence, if you see that your valves need changing more than expected, it is due to a faulty fuel injector.

8. Engine Stalling

A bad fuel injector can cause engine stalling or rough idling. Fuel injectors are designed to supply fluid into the intake manifold. If a fuel injector malfunctions, the amount of fuel being delivered is disturbed.

More or less fuel can lead to incomplete combustion. As combustion process only require the AF (air to fuel) ratio to be 12.5-14:1. A faulty fuel injector deviates from this ratio.

A disturbance in this ratio leads to engine stalling or rough idling.

9. Problems While Starting the Car

If you face problems while starting your car, it might be due to a bad fuel injector. It’s no hidden fact that fuel and air mixture carry out combustion, starting your vehicle.

If fuel injectors are not delivering sufficient fuel, the engine won’t start at all.

So, if you observe that the engine is taking too long to start or its revs have become heavier, you have a faulty fuel injector.

10. Check Engine Warning Light

Any problems with the engine whatsoever might cause the check engine light to come on. Fuel injector issues are no different. A bad fuel injector can also light up your check engine light.

The purpose of check engine lights is to warn the driver before any serious damage. Bad fuel injectors can have serious ramifications. So you need to check for a faulty fuel injector if the check engine light comes on.

Cost of Replacement for a Faulty Fuel Injector

too much fuel

Depending upon your car’s make and model, the fuel injector replacement cost can range between $400 and $950. Economy sectors cars have only 3 or 4 cylinders, so their fuel injector replacement cost will be lower.

However, high-end luxury cars may have 6, 8, or 10 injectors. The average cost to replace each injector is about $200. So, some luxury cars can cost you $2,000 to $3,000 for replacing injectors.

On the other hand, mechanics can do injector cleaning at half the price.


Fuel injectors are the most critical components of the fuel injection system. They can cause rough idle and engine stalls making you feel powerless while driving the car.

Negative impacts on the performance of cars aside, they can cause permanent damage to your vehicle’s engine, so bad fuel injector symptoms should not be taken lightly.

If you observe even one alarming fuel injector symptom, visit a car care professional and clean your injectors immediately. Doing this could save you hundreds of dollars in replacement costs. 

Frequently Asked Questions

Can you clean dirty fuel injectors?

Yes, you can clean a dirty fuel injector. A clogged injector can be caused by dirt and debris trapped inside. Sometimes clogged injectors have become dirtier beyond cleaning, in which case you need fuel injector replacement. Fuel injector cleaning can cost you somewhere between $50 to $100 per injector

How many fuel injectors are there in one car?

Modern cars have one fuel injector for each cylinder. So, usually, a car has 3-8 fuel injectors. But even one failed fuel injector is enough to compromise the performance of your vehicle’s engine.

Can bad fuel injectors compromise the performance of your car?

Yes, very much so. A bad fuel injector can negatively impact the performance of your car. It can cause your vehicle to become sluggish and lower the top speed.

How long can you drive with a bad fuel injector?

You can drive at least 5,000 miles or more with a bad fuel injector. But you should avoid driving with a bad fuel injector as it can damage other parts of the fuel system. You should not ignore bad fuel injector symptoms.

Can short drives lead to a bad fuel injector?

Yes, very short drives can lead to a bad fuel injector. Short drives do not allow for a fuel injector to reach its optimum functioning point. Thus if a car is turned off before reaching optimal working condition, some fuel is left inside the injector. This residual fuel can permanently clog the injectors.

Can a clogged fuel injector cause fuel leaks?

Yes, you might not get a leaking fuel injector. But a fuel leak due to a clogged fuel injector is possible. Several seals and openings in the fuel system can cause a fuel leak.

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