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The Top 6 Signs Of Bad Fuel Injectors

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Although fuel injection dates back to the 1950s on production cars, the technology didn’t become commonplace until the late 1980s. Today, all new vehicles have electronic fuel injection instead of a carburetor. The technology uses individual fuel injectors to deliver fuel to the engine.

Fuel injection is far more efficient and reliable than a carburetor. But like any automotive part, the fuel injectors can eventually fail, resulting in some noticeable symptoms.

fuel injectors of a car
There are two common types of modern electronic fuel injection: port-injection and direct-injection.

The Top Signs of Bad Fuel Injectors in a Gas Engine

Most fuel injectors are simple, electronically-operated devices. The engine computer, which is often referred to as the powertrain control module (PCM), activates each of the injectors to spray fuel into the engine’s cylinders.

A typical fuel injector contains an electronic solenoid and a spring-loaded valve. The PCM activates the solenoid, which, in turn, lifts the valve off of its seat, allowing fuel to enter the cylinder.

There are two common types of modern electronic fuel injection: port-injection and direct-injection. In a port injection system, the injectors are located in the intake manifold, where they spray fuel into the intake ports. On the other hand, with a direct-injection system, the injectors are located in the engine’s cylinder head, where they spray fuel directly into the combustion chamber.

Most vehicles have one injector per cylinder. There are, however, some applications that have two injectors per cylinder—one for the port injection system and one for the direct injection system. Also, there’s an older type of fuel injection technology, called throttle body injection, that uses just one or two throttle body-mounted fuel injectors.

Even though fuel injectors are fairly robust, they can eventually fail either mechanically or electrically. An injector that is clogged or stuck closed will cause the engine to run lean (not enough fuel). Meanwhile, an injector that is leaking internally or stuck open will result in an engine that runs rich (too much fuel).

When one or more of the injectors fail, you’ll likely notice at least one of the following symptoms:

Misfiring and Running Rough

Your car’s engine must receive the proper amount of air and fuel for complete combustion. A faulty injector can cause the engine to run either lean or rich (depending on how the injector fails), resulting in incomplete combustion, which is also known as a misfire. As the driver, you’ll notice that the misfire makes the vehicle run rough and/or hesitate.

Illuminated Check Engine Light

The PCM monitors the injectors and their circuits while also continuously looking for engine misfires. If the module detects a misfire or an injector circuit problem, it will turn on the check engine light and store a diagnostic trouble code (DTC) in its memory.

Abnormal Odors

An injector that is sticking open can allow unburnt fuel to pass through the engine. From there, the fuel enters the catalytic converter, causing the device to overheat and create a rotten egg smell (an issue that will eventually damage the converter).

Also, in some instances, leaking injectors may cause a noticeable fuel smell. In some extreme cases, a stuck direct injector may even allow stinky, raw fuel to pass through the engine and out of the car’s tailpipe!

black smoke coming from tailpipe
If one or more injectors are leaking a substantial amount of fuel into the engine, the vehicle will run rich enough to produce black smoke from the tailpipe.

Black Smoke From the Tailpipe

The PCM can compensate for a rich running condition up to a point. But if one or more injectors are leaking a substantial amount of fuel into the engine, the vehicle will run rich enough to produce black smoke from the tailpipe.

Oil Dilution

If one or more of the injectors are leaking into the engine, fuel may slip past the piston rings and into the crankcase, where it then mixes with engine oil. In instances where the problem is bad enough, the oil level may appear overfull on the dipstick.

Engines that have direct fuel injection tend to be the most susceptible to oil dilution. If the problem is not addressed quickly, severe engine damage may result.

Increased Fuel Consumption

Obviously, a leaking injector will waste fuel. What you might not realize, however, is that anything that causes a misfire—including one or more stuck closed injectors—will also result in increased fuel consumption. In other words: You’ll likely see a decline in fuel economy, regardless of whether the faulty injector (s) are causing the engine to run rich or run lean.

Should You Clean Your Fuel Injectors?

Some experts recommend cleaning your car’s injectors every 25,000 to 30,000 miles. Although some might say that’s overkill, there are definite benefits to cleaning dirty fuel injectors, one of which is that it may save you from having to replace one or more of the injectors.

There are two primary injector cleaning methods. The first is the on-car method, which typically involves using pressurized equipment to run solvent through the injectors. There’s also an off-car procedure, where the technician removes the injectors from the engine, then places them in a dedicated cleaning machine. Cleaning the injectors off of the car provides the best results, but it’s also the most expensive of the two methods.

Also, there are bottles of fuel injector cleaner that you can pour into your gas tank. Some professionals swear by these products, while others feel they don’t do enough on their own without a full-fledged injector cleaning.

mechanic holding fuel injectors
Some experts recommend cleaning your car’s fuel injectors every 25,000 to 30,000 miles.

Fuel Injector Cleaning Cost vs. Fuel Injector Replacement Cost

Cleaning your injectors is almost always less expensive than replacing them. But there are many instances where a simple cleaning will not fix the problem, and the injectors must be replaced.

  • For an on-car injector cleaning, you can usually expect to pay somewhere between $100 and $250.
  • To replace a single injector, most shops will charge somewhere between $150 and $500.

Regardless of whether you clean or replace the injectors, the exact cost of the repair will depend on several factors, starting with the year, make, and model of your vehicle.

Of course, if you have the know-how, you can save a lot of money by replacing the injectors yourself. CarParts.com has a wide variety of replacement injectors available for various makes and models.

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