How to Clean Fuel Injectors

Gasoline vapor deposits left in fuel injector nozzles after an engine is shut down form hard varnish. Over time, it can build up and clog the injectors. Gasoline additives and detergents already mixed into the gasoline you buy help reduce this problem, but they can’t eliminate it entirely. Injectors periodically need to be cleaned. Some experts recommend cleaning the injectors every 25,000 to 30,000 miles to keep them flowing at peak efficiency. Others contend you should clean them only when the car starts running badly.

Cleaning Method 1: Preventives

But first, a word on prevention. In the U.S., most of those generic gas stations with names you’ve never heard of purchase their gasoline from the lest expensive source, sometimes including refiners who, to save a few pennies, may skimp on the engine-protecting detergents added to their product; name brand gasoline filling stations on the other hand are more reliable, many use their ‘special’ additive cocktail in their sales pitches. A special caution for those driving south of the border: just about the only gasoline you can purchase in Mexico, Pemex, is notorious for not only skimping on detergent but also selling dirty (and even watered-down) gasoline.

In addition to using top quality petrol, be certain to change your car’s fuel filter at least once a year.

But if you definitely feel the need to add additional injector-cleaning detergent to your gas tank, two such products that have been recommended to us are Chevron Techron and BG Industries 44K.

Other than using preventives, we do not recommend cleaning fuel injectors as a do-it-yourself project. But, if you insist on cleaning the injectors yourself...

Method 2: On-Car Cleaning

A faster and easier method than removal and cleaning.

Benefits:

Running a commercially available cleaner through the injectors while the engine is running removes many of the deposits on the valves and inside the combustion chambers as well as in the fuel injectors.
It takes only 15 minutes to determine, by running the engine, whether the treatment resulted in resolution of the symptoms of the fouling problem (poor idle, etc.).

Tools:

Fuel injector cleaning kit; the cost will be around $100 at an auto supply outlet.
Long screw driver.

Procedure:

This is the basic procedure – you will still need to follow the instructions that come with the kit.

Either disable the fuel pump and plug the fuel return line (doing this on some cars may set a fault code which must be cleared after the job is completed), or
Install a U-tube so the fuel will return directly to the tank.
Disconnect the pressure regulator.
Connect the cleaning kit to the fuel port on the fuel rail.
Remove the fuel cap from the gas tank to ensure that excessive pressure does not build up in the system. Cleaning kits deliver a large burst of pressure to the fuel system.
Turn the ignition to ensure that, with the fuel-pump shut off, the engine will not turn over.
Open and continue to open the valve on the kit until the fuel pressure reading matches the one appropriate for your vehicle. (See your vehicle's owners or service manual.)
Start the engine to run the cleaning solvent through the injectors and let it run until the solvent is exhausted in about five minutes and the engine shuts down.
Reset the fuel-pump switch and replace the gas cap.
Reconnect the pressure regulator.
Start the engine and check the fuel injectors for proper operation using an extra-long screwdriver as a "stethoscope." Listen for clicking sounds in rapid sequence to indicate a properly operating injector.

Limitations and Considerations:

Badly clogged injectors may not pass enough solvent during a normal cleaning cycle to be thoroughly cleaned.
You may have to do some additional tests such as checking HC and CO levels in your emissions or an injector pressure drop test to confirm that the injectors responded well enough to your cleaning efforts.
Strong solvents may attack rubber and plastic components in the fuel pump, regulator, and fuel lines.
Because of the flammability of the gasoline and solvent you’re working with and the fact your engine needs to be running during this process there is some risk of injury attached to using this method.

Cleaning Method 3: Off-Car

This is not really an option open to the do-it-yourselfer because it requires special equipment that can cost anywhere from $4,000 to $8,300. Because of that and the labor involved, a shop may charge you $40+ per injector for removal and cleaning. (Makes you long for the good old days of carburetion, doesn’t it?)

But it’s a lot cheaper than spending at least twice that to replace ruined injectors with new ones, which is what happens when an injector becomes hopelessly clogged. And injectors can be tested, observed, and compared off the car. An injector that’s not passing as much liquid as the others can be re-cleaned. If that doesn’t work and the injector must be replaced, the injector that needs to be replaced is easily pinpointed.

Cleaning other components

When cleaning injectors, fuel varnish should also be removed from the throttle body and intake tract with an aerosol cleaning solvent. Intake valves and combustion chambers should also be cleaned using a "top cleaner" type of product, especially on engines that burn oil. Replace the spark plugs after performing any kind of engine cleaning; also change the oil and filter.