Symptoms of Bad Fuel Injectors – All You Should Know & Do

Fuel injectors are essential fuel delivery system components that deliver atomized and pressurized fuel into the engine to ensure optimal combustion. Over time, the fuel injectors can become clogged, dirty, or damaged. Hence, you need to know bad fuel injector symptoms so you can tell when these components go bad.

In this article, I’ll explain all you should know about fuel injectors. This includes their working principles, signs they are bad, what to do when they fail, cleaning and replacement cost, and tips and tricks to make them last longer. But first, let’s see their working principles.

bad fuel injector sound

Fuel Injector Working Principles

Fuel injectors spray fuel into the combustion chamber using electronic valves capable of opening and closing several times per second. They have atomized nozzles that evenly spray gasoline into the engine for optimal combustion.

Car manufacturers introduce fuel injectors to replace the old carburetor. This is because the injectors help with fuel economy and reduce exhaust emissions.

Cars typically have one fuel injector per cylinder. So, if you drive a V6 engine, you’ll have six fuel injectors.

The fuel injector’s principal job is to control the fuel that goes into the engine, ensuring the right volume is delivered when needed. By doing so, they ensure maximum power output and efficiency.

The fuel pump exports gasoline from the tank to the injectors through the fuel lines. The powertrain control module (PCM) collects information from various car sensors to determine the right volume and the right time to fire the injectors to spray fuel.

Once the PCM tells the injectors to spray fuel, they spray atomized fuel through their nozzles. The fuel gets burnt in the combustion chamber during the power stroke.

What are the Symptoms of Dirty Fuel Injectors? 

Fuel injectors can fail by clogging or damaging. They will give the same signs regardless of what causes dirty fuel injectors.

The most prominent symptoms of dirty or bad fuel injectors are engine misfiring and rough idling. Other possible signs are fluctuating RPM needle, hard starting, and the car not starting. If you notice these signs, know it is time to clean or replace your fuel injectors.

Rough idling and engine stalling.

Does your car sputter or idle or shake when you stop at traffic sign? That’s one of the bad fuel injector symptoms you should watch out for. It’s telling you that there’s dirt on one or more injectors. The term ‘rough idling’ means the engine has inconsistent revolutions per minute (RPM). Often, you’ll experience a sudden decrease in fuel delivery. If you experience these two, you have a bad fuel injector.

Engine misfire

The most common symptom of a bad fuel injector connector is engine misfire. If your vehicle sputters and the engine is unresponsive, even when you depress the gas pedal, the engine is misfiring. Engine misfires can cause vibrations that you can feel even while sitting behind the steering wheel. The common cause of engine misfires is improper air-fuel ratio due to faulty fuel injectors.

High fuel consumption

High fuel consumption is a common bad fuel injector symptom in diesel and petrol engines. If you notice you have been visiting the fuel stations more often, it’s due to inefficiency in the air-fuel ratio. You have to diagnose and fix this problem. Spending money on gas won’t do the trick.

Fuel leaks

If you have a cracked or broken fuel injector due to age or anything, fuel will leak from the injector. The most common leaking fuel injector symptom is fuel around the fuel injector areas. The fuel leak indicates that part of the fuel that was supposed to enter the engine is leaking out. In such cases, the injectors are usually fine, but the leak comes from a cracked or broken O ring.

The RPM needle starts fluctuating.

Technically, we control the gauges on the car dashboard. The fuel gauge moves from F to E when you drive a lot with a full tank. And when you accelerate the car, the speedometer travels from 0 to 60 in a predictable manner. But if there’s dirt on the fuel injectors, the RPM will make unpredictable movements.

Car not starting

The principal job of the fuel injectors is to supply fuel to the cylinders. If this job is not done, there won’t be fuel in the combustion chamber for the power stroke, meaning the vehicle will not start.

While it is hard for all the fuel injectors to fail at once, an improper air-fuel ratio due to some bad injectors can prevent the vehicle from starting. However, several other factors can prevent your car from starting.

how to test for a clogged fuel injector

What to do if your car fuel injectors are bad or dirty

Driving with a bad fuel injector is frustrating and unnerving. Hence, you must take the necessary actions when you notice the above signs.

Check for leaks

The first thing is to visually check the injectors for leaks. Often, it could be the injectors are good, but you have a damaged injector seal. If any injector is leaking, remove it, see if the leak is from the O ring, and replace it as needed. If the leak is from the injector itself, replace it with a new one.

Scan the vehicle

If the injectors are not leaking, scan the vehicle. Get a scan tool and locate the OBD port underneath the steering wheel. Connect the scan tool and pull out the registered error codes. If you see error codes P0171 or P0174, it shows you have a lean air-fuel ratio, which could be caused by a lousy injector. A P0200 error code means the injector circuit is malfunctioning.

Test the injectors

The next thing is to remove the injectors and test them to determine the bad ones. Clean or replace the lousy injector as needed. I published an article on how to clean fuel injectors. Check the article to guide you on how to clean dirty fuel injectors. After that, reinstall the injectors and get your car back on the road.

Contact a mechanic

If you’re not a DIYer, the most feasible solution is to contact a mechanic. The mechanic will track the cause of the problem and rectify it.

How much does it cost to replace new fuel injectors?

The cost of replacing fuel injectors depends on factors like your vehicle design and the number of injectors you want to replace. If you want to replace the injectors yourself, you can replace only the bad ones. But if you want a mechanic to replace it, he may replace the entire injectors for a balanced fuel delivery across all the cylinders.

The replacement isn’t work-intensive, and most of what you pay is for the parts and not the labor.

With all this in mind, you can expect to pay between $200 and $700, depending on the injectors needed, your location, and how easy it is to access the fuel injectors.

How much does it cost to clean fuel injectors?

Cleaning fuel injectors is an easy task. You can even clean the injectors without removing them. But if you want a professional to clean it, budget $75 to $150. Of course, the price can be quite lower than $75, but it won’t exceed $150.

Tips and tricks to keep long-lasting fuel injectors

As the saying goes, prevention is better than cure. It’s better to prevent something than to address it when it has already happened.

The fuel injectors carry out the principal role of sending fuel into the engine for combustion. We often forget how important this is until the injectors begin to malfunction.

Here are the most appropriate ways to extend the fuel injectors’ shelf life.

  • Avoid low-quality fuel
  • Keep the injectors clean
  • Always buy fuel additive whenever you refill your tank
  • Clean or change fuel filters

Learn More about the Symptoms of a Bad Fuel Injector by watching YouTube Video. 

Final Words

There are several signs of failing or dirty fuel injectors. I have outlined the common ones in this article. If you are experiencing any of the signs above, check the fuel injectors and rectify the problem.

If you don’t trust your gut or you’re not a DIYer, contact an automotive mechanic to diagnose and replace the bad fuel injector.


Hi there, I am R. Hasan Tito, a mechanic, and owner of this website. My friend and I created this website to share our knowledge, expertise, and experience with our fellow mechanics' community and car users. I am a specialist and certified automotive mechanic (Both Heavy Commercial and Private Cars). I worked as a Mechanic and Mechanic Supervisor for over fifteen years at Global Rebound Automotive companies - Toyota, TATA, BMW, Nissan, TVs, and Others. Now, I enjoy my new role of leading a team of automotive experts (in their respective fields) and publish new content on a regular basis on my website and social media.

One thought on “Symptoms of Bad Fuel Injectors – All You Should Know & Do

  1. Am learning alot from this channel….I am almost being a mechanic, thanx

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