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In electronic fuel injection (EFI) engines, the fuel injectors to deliver precise amounts of fuel to each cylinder. There may be one or more fuel injectors per cylinder, and even cold-start fuel injectors in the intake. Fuel injectors are tiny electrically-controlled valves, which can open and close in mere fractions of a second. Each time the fuel injector opens, fuel sprays into the cylinder.


When investigating symptoms like poor engine performance, cylinder misfires, or high emissions, dirty fuel injectors could be the cause. Over time, debris or fuel contaminants can block tiny fuel injector orifices. Chemical deposits can also clog fuel injectors. Partial blockage could lead to poor fuel spray and poor engine performance. Partial blockage could increase fuel consumption and emissions, dilute engine oil, or damage catalytic converters. Complete fuel injector blockage could lead to hard starting, rough running, poor performance, and higher emissions.


Cleaning fuel injectors isn’t always easy, however, depending on which method is necessary to restore performance. If fuel injector performance doesn’t improve after addition of an in-tank fuel injector cleaner, you’ll need a more intensive method.

Basically, there are two methods to clean fuel injectors, on-car cleaning and bench cleaning. On-car cleaning is less expensive and quicker, but not as thorough as bench cleaning. Also, on-car cleaning can’t address external fuel injector deposits as well as bench cleaning. Still, on-car cleaning is regularly suggested and is often effective.


On-Car Fuel Injector Cleaning

On-car fuel injector cleaning forces pure fuel injector cleaner into the fuel rail, which can usually address fuel system deposits that an in-tank cleaner can’t. This requires a special tool to tap into the fuel line. The special tool might run off its own compressed canister of fuel injector cleaner or may need an air compressor to force the cleaning solution into the fuel rail. Basic steps are as follows:

With vehicle running, disconnect fuel pump fuse, relay, or connector, and let the engine run until the fuel pressure drops. This might take a few minutes, but it’s safer than simply cracking open a fuel line and letting raw fuel run out.

1. Turn the key to the OFF position and wrap rags around the fuel line disconnect. This will catch any fuel drip when you open the fuel line. Using basic hand tools or fuel line disconnect tools, disconnect the fuel rail from the fuel supply line. Skip this step if you connect to the fuel rail via the fuel pressure test port.
2. Using the appropriate adapter, connect the fuel injector cleaner to the fuel rail and apply pressure. This may be from the fuel injector cleaner can or compressed-air supply.
3. Start and run the engine between idle and 2,500 rpm, running the engine until the cleaning solution is used up, at which point the engine will sputter out.
4. Disconnect the fuel injector cleaner and reconnect the fuel line. Also, replace the fuel pump fuse, relay, or connector, whichever was removed at the start.
5. Restart your vehicle and take it for a test drive. It may start rough, at first, but should smooth out as proper fuel pressure and flow is restored. Consider an intake cleaning service to address external fuel injector deposits and intake deposits.

Caution: These steps are for basic EFI systems but may not apply to gasoline direct injection (GDI) systems, which run at significantly higher pressures. Do not work on a GDI system unless you know what you are doing, as severe injury may result. Other basic raw fuel safety procedures apply, like working in a well-ventilated area, avoiding smoking and open flames, and appropriate protective gloves and safety glasses.

Bench Fuel Injector Cleaning

In case on-car cleaning doesn’t cut it, the only other options are fuel injector replacement or fuel injector bench cleaning. Depending on cost and availability of new fuel injectors, bench cleaning may be a good option. This will require removal and replacement of the fuel injectors, the same as replacing with new parts, but with an additional cleaning process. A shop would use special tools, but at home can be done with fuel injector cleaner.

1. Just as with the on-car cleaning, you need to drain the fuel pressure, which you do by running the engine with the fuel pump disconnected or unpowered. After a few minutes, the engine will sputter out and you can remove the fuel rail and fuel injectors.
2. Removing the fuel injectors will depend entirely on the year, make, and model of the vehicle. One some vehicles, the fuel injectors are readily accessible, while others make it difficult to access.
3. Once the fuel injectors are removed, each one can be cleaned individually. Use a soft-bristle brush and carburetor cleaner or EFI cleaner to clean the outside of the fuel injectors.
4. Use a fuel injector jumper to energize the fuel injector to open it up. You might be able to make a simple jumper with a 9 V battery and wires. Then, spray cleaner through the fuel injector from both directions.
5. After cleaning, reinstall the fuel injectors with new O-rings, reconnect the fuel pump, and start the engine.

Maintaining Clean Injectors

Whether you’re driving a new car, old car, or you’ve just cleaned the fuel injectors, you’ll want to keep your fuel injectors clean for as long as possible. There are three ways to keep your EFI system flowing and your engine running:

• Use TOP TIER detergent fuels (this is not the same as octane level). Only certain brands are classified as TOP TIER, whose fuel contains detergents to keep EFI systems running clean with every fill-up.
• If not using TOP TIER fuels, in-tank fuel injector cleaner every 5,000 miles will make up for the detergents not added in the fuel.
• Drive regularly. There’s nothing a vehicle can’t endure more than not being driven. As stagnant fuel ages, it can separate and evaporate, leading to the formation of deposits in the EFI system. If you must park your vehicle for a time, add fuel stabilizer to the last tank of the season and run the engine at least 15 minutes to get stabilized fuel to the injectors.