Fuel Injector Problems

Updated February 21, 2017

Fuel injectors deliver the air-fuel mixture to the engine cylinders in many cars. Problems with these devices can lead to several noticeable decreases in performance and function. Familiarising yourself with the potential problems and their causes may help you diagnose faulty fuel injectors early and return your car to good working order more quickly.

How Fuel Injectors Work

A fuel injector delivers gasoline to the combustion chamber by using an electrical solenoid valve. When the car is started, an electrical current is sent to the injector coil. This current causes the coil to form a magnet. The magnet pulls a device known as a pintle from the front of the valve, allowing gasoline to flow through. When the current is shut off, the magnetic field ceases to exist and the pintle goes back into its resting place and blocks the flow of fuel.


Fuel restriction, regardless of the underlying cause, is the most common reason for reduced performance in a fuel injected system. According to, an 8 to 10 per cent restriction in fuel in just one of a car's injectors can cause a misfire. A misfire causes unburned oxygen to force a lean reading in the oxygen sensor. This reading will cause the other injectors to compensate by staying open too long, which will cause too rich of a fuel mixture in the other cylinders. This can be damaging to the engine in some cases.

Heat soak is a common cause of fuel restriction. Heat soak happens when an engine is shut off. The residual heat from the engine evaporates the fuel that remains in the injector, leaving behind waxy compounds known as oilfins. Since the engine is off, nothing will flow through the injectors to wash away the oilfins and they harden and form deposits that restrict the fuel flow through the injector.


All gasoline is not created equal. Unfortunately some producers attempt to save costs by reducing detergent levels, or by switching to less effective detergents.

Detergents control deposits the gas leaves behind in the system. The less effective detergents tend to leave behind more build-up that may cause clogging in the fuel injector system.

According to, as much as 85 per cent of the gasoline being sold in the U.S. contains less than the recommended amount of fuel additives to control this problem.


Injector cleaning procedures to clear out deposits and reverse fuel restriction can vary from a fuel injector cleaner solution bought from the store and poured into the tank to the removal of the injectors for cleaning.

More involved cleaning procedures are classified as on-car or off-car cleaning. On-car cleaning takes place without the removal of the fuel injectors. Using pressurised equipment, a solvent is run through the fuel line while the engine is running. The solvent will remove any deposits in the injectors and valves and inside the combustion chamber in many cases . For the worst problems with dirty injectors, a mechanic will remove the injection system and give them a more thorough cleaning. This process may include the use of an ultrasonic bath in the most severe cases.


Symptoms that a car's fuel injection system is having problems may include rough idling, misfiring, hesitation when attempting to accelerate, and a noticeable loss of power and decreased fuel economy. In many cases where strict emissions testing is required, a fuel injector problem can make your vehicle produce considerably more emissions, according to

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About the Author

Lee Morgan is a fiction writer and journalist. His writing has appeared for more than 15 years in many news publications including the "Tennesseean," the "Tampa Tribune," "West Hawaii Today," the "Honolulu Star Bulletin" and the "Dickson Herald," where he was sports editor. He holds a Bachelor of Science in mass communications from Middle Tennessee State University.