Symptoms Of Bad And Dirty Fuel Injectors (Know The Difference)

The perfect mix of air and fuel determined for combustion, eventually travel into the cylinders through the fuel injectors. Fuel injectors are designed to deliver a consistent and atomized stream of the fuel into the system to combust in the most efficient manner, ensuring the least amount of toxic exhaust. They also help in a more variable delivery of fuel as well as a more consistent transient throttle response.

But due to their tight tolerance and tinier-than-pin nozzles, fuel injectors can often accumulate dirt. This can disrupt their spray pattern and prevent them from working properly.

In rare cases, a fuel injector can also go bad where its solenoid-operated valve may not respond appropriately to the signals from the ECU.  

In both cases, you may experience an anomaly in fuel delivery and witness a noticeably poor engine performance. But before delving into the symptoms of bad or dirty fuel injectors in detail, lets understand how they work. 

How it Works

There are a few different types of fuel injection systems that vary in the manner in which they spray fuel into the system, So without delving into the minutiae we’ll quickly go over how the electronically controlled fuel injector itself works.

The process of delivering fuel to the cylinders actually begins from the back of your vehicle where the fuel tank is located. The fuel pump transfers pressurized fuel right from the tank to the tip of the injector nozzle. There are a couple of other mechanisms in place between its path that filter and regulate the pressure but we won’t be getting into that right now.

The high-pressure fuel from the fuel rail goes through the top of the injector into the reserve, beneath which there is an electromagnet that’s controlled by the ECU. it regulates when the fuel injector will fire and for how long. When the ECU sends the signal for injection, the electromagnetic coil pulls the plunger up, opening the pintle injector to delivers the atomized fuel out of the nozzle. 

Know the Difference 

Let’s first draw the distinction between dirty and bad fuel injectors. Dirty fuel injectors will hinder the fuel supply and cause the engine to run lean whereas a bad fuel injector that is broken or doesn’t close for some reason would typically have the engine run rich. If the bad fuel injector has no pulse or is firing very little it may have an effect similar to lean condition but it’s highly unlikely for more than one injector to go bad at the same time.

It’s important not to confuse the two as a fuel injector that is leaky or is stuck open can produce the exact opposite effect of what dirty injectors would have.

More importantly, you do not want to throw the baby out with the bathwater. If you have dirty fuel injectors, replacing them would not solve the problem. Similarly, cleaning a fuel injector that has gone bad would only waste your time.

Symptoms of Dirty Fuel Injectors

Fuel injectors have extremely tiny nozzles which make them highly susceptible to fine pieces of sediments and dirt. And though they get a highly pressurized stream of liquid that could help let out some dirt, there are few other reasons including bigger pieces of debris that can eventually lead them to get gunked up.

It is recommended to have your fuel injectors cleaned every 30000 miles or so, but if you fill your gas tank with fuel that’s questionable in quality, you could probably dirty them much quicker.

Starting problems

During ignition when the fuel pump primes, it sends a pressurized flow of fuel. This fuel needs to be atomized and sprayed into the cylinder by the fuel injectors. But if the fuel injectors are dirty, they may create a delay in sending the fuel out, causing low power for the engine to turn over.

Further, dirt may also cause the injectors to fire erratically, and make the combustion inefficient.

Lack of power

Another common symptom of dirty fuel injectors is a loss of power. Due to the restriction, dirty or clogged fuel injectors tips can create, how much fuel actually goes into the cylinders can be reduced. And as a result, you may either have trouble starting or the vehicle may crank a bit before starting over.

Fluctuating Revvs

One of the defining elements of fuel injectors is a consistent injection of fuel across all cylinders. 

Intermittently you may also observe the engine revs go up and down. This unintentional surge is due to uneven dispersion of fuel as the injectors may at times miss the fuel delivery completely leading to improper amounts to be supplied at the next injection.

Engine Overheating  

When the dirty injectors deliver too little gas, it can cause the engine to burn lean, producing a lot less power but consequently a lot more heat. Such abnormality is typical of incomplete combustion where the mixture is not properly burnt to generate enough power through does generate higher amounts of heat because of slower combustion. 

Engine misfires

Frequently, you may also notice misfires in the engine as the dirty fuel injector would not be able to able to fire a consistent stream of fuel into the cylinders which would lead to improper combustion.

Due to the lowered amounts of fuel entering the system at idle and at low speeds to you may find the sputters to be particularly high in those instances while as the fuel flow increases you may observe the engine quieting down.


An engine can quit operations due to a number of reasons but most notably stalling can be attributed to a blockage in fuel flow. If the fuel injectors are severely clogged you may occasionally find the car abruptly stalling out on you. This may happen when two or more injectors stop firing at the same time probably due to stuck debris.

Check Engine Light

Finally, you may also find your check engine light to come on. As the engine struggles to operate in fluctuating fuel pressure, the internal diagnostics will inform you of the impending damage such a condition may incur.

However, a check engine light could mean a number of different things. To narrow down the problem with the fuel system it is recommended to have your car scanned for trouble codes by a professional as in most cases the engine light can be an indication of potential damage to the engine.

Symptoms of Leaky Fuel Injectors

A bad fuel injector is a rare scenario. It occurs when the injector dies out, meaning the electromagnetic coil inside the injector is no longer responding to the commands from the ECU. 

In such a case, the injector may spray very little or no fuel into the system. This sort of issue may cause similar effects as dirty fuel injectors but it’s highly unlikely that you will have all the injectors go bad as opposed to dirt which accumulates pretty consistently and evenly on all the nozzles. 

Developing a leak around the injection system is also quite rare but it can have completely the opposite effect on your engine than what dirty injectors would have. You may have an issue with the injector either because of torn or improperly fitted o-rings or due to an injector nozzle that is stuck open for some reason. 

Leaks Around The Engine Bay

The most evident sign of a leaking fuel injector is visible gasoline around your engine. The fuel rail itself would be the most common place to look for a fuel leak. If you find fuel to squirt out even in small amounts from one of the injectors when the engine is running, you need to have the injectors inspected for damage and replaced as soon as possible.

This can actually be the earliest sign you can find for an injector leak as it clears up any doubt around where the fuel may be coming from. But typically, it’s not common for everyone to look under the hood every time they start their engine so you might have missed this early sign.

Smell Of Gasoline

The next best alternative to a visible leak is the unmistakable smell of gasoline. Driving with a fuel leak can be a safety issue and the smell cannot necessarily be traced to a leak in the engine block but if you suspect having bad fuel injectors you may want to look under the hood first.

The smell can also inform you of the severity of the leak, if the leak is too critical, possibly, due to more than one injector you would smell a stronger odor in your car. However, you should not miss to look other places for a leak as a gasoline leak can turn into a bigger problem.

Bad Gas Mileage 

Generally, the ECU controls what’s known as the Injector pulse width which essentially prevents the injectors from firing any amount beyond the duration the ECU has set. Even if the fuel injectors are dirty, the nozzle is controlled by the computer. But if the nozzle is stuck open somehow, it may not cease to fire and cause an immoderate amount to be injected into a particular cylinder.

You may notice a relatively high gas mileage depending on the severity of the leak and the number of injectors that have developed such a leak. It is rare that you would have more than one injector go bad at the same time though if the vehicle has recently sustained damage, it could be a possibility.

Black Smoke 

As a consequence of less than ideal fuel ratios and the uncontrolled pouring of such, the engine will end up dumping what couldn’t be contained in the exhaust as a means of clearing out. It is extremely hard on the engine to process all that fuel in addition to more unceasingly being injected in and as a result much of the fuel to be burned actually combusts in an inefficient and incomplete manner.

This unburned fuel when reaches the exhaust has to be processed and disposed of, producing black smoke that is typical of unprocessed fuel.  If you see black or dark grey smoke coming out of your tailpipe it is a clear indication of a rich condition. Further down the line, a rich condition especially created with a fuel leak can wreak havoc on other vital and some really expensive components such as the catalytic converter, spark plugs, and pistons.

Hydrostatic Lock

Another symptom of a bad or leaky injector that isn’t commonly heard of is a hydrostatic lock. A hydrostatic lock occurs essentially when an incompressible fluid enters the cylinders. The fuel injectors are meant to atomize the air-fuel mixture sending in a gaseous mix into the system for easy compression. But when a fuel injector develops a leak typically a substantial one, it may pour in fuel in its liquid form. 

This may either cause the vehicle to go under lock and not operate or if the leak is small, continue to run with constant internal damage. In any case, a leak will eventually cause the vehicle to lock if not tended to soon. In a hydrostatic lock, an engine goes out suddenly and often with a big thud sound. This is also to prevent the damage it may have on the pistons, connecting rods, and valves.

Higher Emissions

Though you might not be aware of such a problem in the least until taking the next emissions test, leaking fuel injectors can surely be a culprit in worsening your vehicle’s emissions. As mentioned the constant and immoderate injection of fuel leads to improper combustion. The bi-product of such combustion would be more hydrocarbons and various other gases that are toxic to the environment.

How To Easily Check Your Fuel Injectors

Usually, to check fuel injectors you would need a multimeter and it can be actually very helpful to identify the bad ones. It can tell you precise voltages that you can compare each injector with to separate the odd one out. 

However, not everyone has a multimeter or knows how to use one. So we’re going to use another method that is quite commonly used and works dependably well.

To check your fuel injectors using this method you would only need a screwdriver, ideally a long and sturdy one.

When you turn on your car the injector valves open and close consistently and rhythmically, producing a tapping noise which is exactly what you need to carefully listen for.

So, just turn on the vehicle and place the metal end of the screwdriver on one of the injectors and the other end near your ear. Now listen for the clicking noise. It should be nice and consistent without a drop. Test out each injector separately in the same manner and hopefully, you’ll find the one that stands out.


If you find a leak in one of your injectors, it best to replace it immediately. A fuel leak is a serious issue that needs immediate action. Though if you have dirty fuel injectors, you could use a little DIY cleaning or have them taken care of by professionals at your periodic car service.

You may also like...

Leave a Reply

Your email address will not be published.

Share via
Copy link
Powered by Social Snap