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How to Clean Fuel Injectors

Dan Ferrell writes about DIY car maintenance and repair. He has certifications in Automation and Control Technology and Technical Writing.

Partially blocked or clogged fuel injectors will affect engine performance.

Partially blocked or clogged fuel injectors will affect engine performance.

You may need to clean or replace a fuel injector(s) if your engine is experiencing one or more of the following symptoms:

  • hard-stars
  • hesitation
  • rough idle
  • power loss
  • sputtering
  • misfires
  • increased emissions

Fuel injectors' tiny nozzles are calibrated to inject fuel at a precise flow rate, as commanded by the car's computer, depending on engine load and other operating conditions. But it doesn't take much stuck impurities and chemical compounds to restrict or block fuel flow. After shutting down your engine, heat evaporates the residual fuel in the injector's spout; but gradually, it also 'glues' tiny hydrocarbon particles (blow-by and contaminants) to the nozzle's walls as varnish.

After miles of operation, buildup accumulates around the head of the injector as well, distorting the original fuel spray pattern and restricting or blocking fuel flow. This will cause the engine to idle erratically, make it hard to start and misfire. When the problem has just started, you still may have a chance to remove these deposits using special fuel additives designed to clean and clear fuel injectors. But badly plugged injectors will require a most drastic solution.

Unfortunately, dirty injectors are not the only ones that can give you these same symptoms. If your problem is dirty injectors, this guide will help you get them back into shape. However, if your injectors seem to be cleaned, or the symptoms persist after cleaning the injectors, you'll find a list of components that you may want to inspect to find the source of the problem.


I. Cleaning Fuel Injectors at Home

II. Taking your Car to the Shop

III. What if My Fuel Injectors Are Not Clogged?

IV. Preventing Clogged Fuel Injectors

I. Cleaning Fuel Injectors at Home

With the quality of fuel available today, and the additives and detergents that some brands mix in, it's usually not necessary to service fuel injectors. At least not too frequently. Nevertheless, a fuel injector valve's passage can clog over time, especially if you use low quality fuel, drive mostly short trips, or your engine has accumulated high mileage.

Most drivers don't use any additives to prevent this type of problem with their fuel injectors. But, if you've noticed one or more of the symptoms described at the introduction, you may still be on time to prevent an expensive repair. Next time you go to fill up the tank, add a quality fuel injector cleaner to the tank before you pour the fuel. Seafoam motor treatment is a popular and quality product for this purpose. I've used it myself with good results. Other products you might want to try as well are Techron injector cleaner and Marvel Mystery Oil. Then, finish filling up the tank.

Besides helping clear fuel injectors, some of these products have other benefits like help control moisture in the fuel tank, and removing carbon deposits from valves and cylinders.

Carefully read the manufacturer instructions that come with the product you decide to use.

However, if one or more fuel injectors are severely clogged, a fuel injector cleaning kit or a visit to the shop may be a better option for you. Follow the manufacturer instructions when using special kits at home. If your engine has a returnless fuel injection system and one or more of the fuel injectors are plugged, you may want to remove the fuel rail for cleaning as well.

To prevent injectors from clogging, use only gasoline with high content of fuel cleaning additives, or add a good fuel system cleaner to the tank at least every 3000 miles.

Sometimes it's necessary to remove the injectors to clean them.

Sometimes it's necessary to remove the injectors to clean them.

II. Taking Your Car to the Shop

If you've decided to take your car in for service, do some research before going to the first repair shop offering a great deal on fuel injectors service. You may see shops advertising a cheap fuel injection cleaning job that consists of a solution added to the fuel tank, which you can do yourself at a low cost.

For a deep cleaning job, shops use a pressurized cleaning system with strong chemicals to dissolve hard to remove deposits. With an 'injectors in-place cleaning operation', a special solution is run through the fuel rail with air pressure to help remove carbon buildup and hard to remove varnish inside the injectors.

On tough jobs, a shop will recommend removing the injectors from the fuel rail and cleaning them separately. You pay more for this type of service (about $20 to $30 dllrs. per injector) but not as much as you would if you had to replace the injectors.

Either of these methods is a good option when working with hard to clean injectors.

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A partially restricted fuel filter can show the symptoms of a restricted fuel injector.

A partially restricted fuel filter can show the symptoms of a restricted fuel injector.

III. What if My Fuel Injectors Are Not Clogged?

Unfortunately, partially or completely clogged fuel injectors are not the only reason for bad engine performance. Other problems, like a malfunctioning injector, restricted fuel filter, fuel system in need of maintenance, or even a failing sensor may produce symptoms similar to those of a restricted fuel injector, affecting fuel delivery.

After cleaning the fuel injectors, if engine performance problems persist, here is a list of maintenance items—including sensors—that you might want to check to help you restore fuel economy and proper engine performance.

The vehicle service manual for your particular model comes in handy when checking, troubleshooting, replacing, or servicing engine components or systems, including those listed next. You can buy an inexpensive aftermarket repair manual online like this Haynes manual at Amazon. Haynes manuals come with step-by-step instructions, illustrations and photos for many maintenance, troubleshooting or repair projects you can do at home.

1. Checking fuel injectors' operation

Fuel injectors passages not only may become plugged after miles of operation; they also may fail. And both conditions may show similar symptoms. You can use a simple test at home to check that each injector is operating.

Use a mechanic's stethoscope or large screwdriver to listen to each injector opening and closing (a clicking sound) as the engine idles.

  1. If you want to use a screwdriver, place the driver's tip against the injector's body and the end of the driver's handle against you ear.
  2. Place your transmission in Park (automatic) or Neutral (manual).
  3. Chock the rear wheels.
  4. Start the engine and let it idle.
  5. Pop the hood open and start listening to each injector. If you don't hear the injector's clicking, you might've found a dead fuel injector.

To confirm your findings, consult your vehicle repair manual. Most likely your manual has the instructions to check the injectors' resistance using a digital multimeter. Lower than specified resistance or infinite resistance will indicate a failed injector. Watch the next video so that you have an idea how you can check an injector's resistance yourself.

If necessary, follow your service manual's instructions for further tests.

2. Servicing fuel and air filters

These filters represent common, but often overlooked, maintenance items. Consult your car owner's or vehicle service manual for the filters' replacement interval. Replace them if necessary. Over time, dust and foreign particles clog the filter element, restricting fuel or air flow.

If you haven't followed the recommended service intervals, the fuel filter may have started to interfere with fuel flow (just like a dirty fuel injector) and fuel pump operation. Failing to replace a restricted or clogged fuel filter will cut short the fuel pump's service life as well.

If your manufacturer didn't schedule a fuel filter service interval, replace it at least every 12 months to guarantee proper fuel flow. Also, replace the air filter every two years, or every year if you drive mostly in dusty areas or within the city.

3. Checking ignition system components

Your vehicle service manual shows you how to check and replace the different components in the ignition system for your particular vehicle model. Problems in this system may produce symptoms similar to those of plugged fuel injector. Check spark plugs, spark plug wires, distributor and ignition coil.

4. Cleaning the throttle body

Check and clean, if necessary, the throttle body as well. Removing the layer of carbon buildup around the throttle bore and throttle valve will clear the passage and make sure the throttle plate closes properly, preventing rough idle. Spray some carburetor cleaner on a clean rag and use the rag to clean the throttle body.

5. Checking the fuel pressure regulator

This is another important component to check. Inspect the vacuum hose connected to it (on vacuum operated regulators), the condition of the electrical connector and wires. Also, consult the service manual for your particular model for the correct way to check the fuel pressure regulator on your vehicle, whether the regulator is located in the fuel rail or in the fuel pump module.

6. Manifold absolute pressure

The Manifold Absolute Pressure (MAP) sensor reads engine vacuum and sends the appropriate signal to the vehicle's computer. The computer uses this signal to regulate fuel, ignition timing, and other engine performance events. Inspect the electrical connector and vacuum line, if used. If necessary, your service manual will help you troubleshoot the sensor.

A malfunctioning oxygen sensor will affect engine performance as well.

A malfunctioning oxygen sensor will affect engine performance as well.

7. Inspecting the oxygen sensor

Inspect the oxygen sensor's electrical connector and the sensor itself. A malfunctioning oxygen sensor will upset the fuel injection and emissions system. A bad oxygen sensor may cause the car's computer to feed too much or too little fuel to the engine, affecting engine performance.

8. Checking the Throttle Position Sensor (TPS)

A malfunctioning TPS will prevent the computer from metering correctly fuel delivery as well, sometimes preventing the engine from starting. Inspect the TPS electrical connector and wires condition.

9. Other Sensors to Keep in Mind

Here are other sensors you may want to pay attention to:

  • Engine Coolant Temperature (ECT) sensor
  • Intake Air Temperature (IAT) sensor
  • Mass Air Flow (MAF) sensor

10. Using a Scan Tool

Retrieving potential diagnostic trouble codes (DTCs) from your vehicle computer system can really help when diagnosing hard to locate the source of problems. If you don't have a scan tool or code reader, stop by your local auto parts store, most will download the codes for you at no cost.

If you decide to buy a scanner, you'll find relatively inexpensive scan tools at most auto parts stores and online.

The following video gives you an idea about using a scan tool to check for malfunctioning sensors that might be affecting engine performance.

Depending on the type of fuel delivery system on your car—conventional, pulse-modulated or direct injection—you may find fewer or more components and sensors affecting the fuel system on your vehicle than those listed here. Consult your vehicle service manual for this information and follow your manual's guidance.

IV. Preventing Clogged Fuel Injectors

The best way to avoid common fuel injectors problems is to prevent dirt, contaminants and buildup from clogging passages in the first place. Add a quality additive to the fuel tank at least every 3000 miles, or when changing the engine oil. And change the fuel filter every year as well. You'll reduce the possibility of breakdowns, save on fuel and prevent costly repairs.

Test Your Knowledge of Fuel Injectors Troubleshooting

For each question, choose the best answer. The answer key is below.

  1. Can you use an ohmmeter to check for a EFI fuel injector's coil for opens or shorts?
    • True
    • False

Answer Key

  1. True

© 2016 Dan Ferrell


Joseph Jj from Ethiopia on September 03, 2019:

Thanks a lot. very important direction. Another help along the way. please would u help on how to test an engine whose ignition ring and valve seal are just replaced with new ones. I'm frustrated not to damage my engine.

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