Fuel Injector


Before covering the typical cleaning systems available and discussing how they are used, several cleaning precautions are in order.

  • Never soak an injector in cleaning solvent. Not only is this an ineffective way to clean injectors, but it most likely will destroy the injector in the process.
  • Never use a wire brush, pipe cleaner, toothpick, or other cleaning utensil to unblock a plugged injector. The metering holes in injectors are drilled to precise tolerances.
  • Scraping or reaming the opening may result in a clean injector but it may also be one that is no longer an accurate fuel-metering device.

The basic premise of all injection cleaning systems is similar in that some type of cleaning chemical is run through the injector in an attempt to dissolve deposits that have formed on the injector's tip.

The methods of applying the cleaner can range from single-shot, pre-mixed, pressurized spray cans to self-mix, self-pressurized chemical tanks resembling bug sprayers.

Pre-Mixed Systems

The pre-mixed, pressurized spray can systems are fairly simple and straightforward to use since the technician does not need to mix, measure, or otherwise handle the cleaning agent.

  • Automotive parts stores usually sell pressurized containers of injector cleaner with a hose for Schrader valve attachment.
  • During the cleaning process, the engine runs on the pressurized container of unleaded fuel and injector cleaner.
  • Fuel pump operation must be stopped to prevent the pump from forcing fuel up to the fuel rail.
  • The fuel return line is plugged to prevent the solution in the cleaning container from flowing through the return line into the fuel tank.
  • Disconnect the wires from the in-tank fuel pump or the fuel pump relay to disable the fuel pump.
    • If you disconnect the fuel pump relay on General Motors products, the oil pressure switch in the fuel pump circuit must also be disconnected to prevent current flow through this switch to the fuel pump.
  • Plug the fuel return line from the fuel rail to the tank.
  • Connect a can of injector cleaner to the Schrader valve on the fuel rail and run the engine for about 20 minutes on the injector solution.

Self-Mixed Systems

Other systems require you to assume the role of chemist and mix up a desired batch of cleaning solution for each application.

  • The chemical solution is placed in a holding container and pressurized by hand pump or shop air to a specified operating pressure.
  • The injector cleaning solution contains unleaded fuel mixed with injector cleaner.
  • The container hose is connected to the Schrader valve on the fuel rail.
Injector cleaner connected to a fuel rail. Courtesy of OTC Tool and Equipment, Division of SPX Corporation.
  • Disable the fuel pump according to the car manufacturer's instructions (for example, pull the fuel pump fuse, disconnect a lead at pump, etc.).
  • Clamp off the fuel pump return line at the flex connection to prevent the cleaner from seeping into the fuel tank.
  • Before starting the engine, open the cleaner's control valve one-half turn or so to prime the injectors, and then start the engine.
  • If available, set and adjust the cleaner's pressure gauge to approximately 5 psi (34.47 kPa) below the operating pressure of the injection system and let the engine run at 1,000 rpm for 10 to 15 minutes or until the cleaning mix has run out.
  • If the engine stalls during cleaning, simply restart it.
  • Run the engine until the recommended amount of fluid is exhausted and the engine stalls.
  • Shut off the ignition, remove the cleaning setup, and reconnect the fuel pump.
  • After removing the clamping devices from around the fuel lines, start the car.
  • Let it idle for 5 minutes or so to remove any leftover cleaner from the fuel lines.

In the more severely clogged cases, the idle improvement should be noticeable almost immediately. with more subtle performance improvements, an injector balance test verifies the cleaning results.

Once the injectors are clean, regularly use an in-tank cleaning additive or a detergent-laced fuel.

After the injectors are cleaned or replaced, rough engine idle may still be present. This problem occurs because the adaptive memory in the computer has learned previously about the restricted injectors. If the injectors were supplying a lean air/fuel ratio, the computer increased the pulse width to try to bring the air/fuel ratio back to stoichiometric.

With the cleaned or replaced injectors, the adaptive computer memory is still supplying the increased pulse width. This action makes the air/fuel ratio too rich now that the restricted injector problem does not exist. With the engine at normal operating temperature, drive the vehicle for at least 5 minutes to allow the adaptive computer memory to learn about the cleaned or replaced injectors. Afterward, the computer should supply the correct injector pulse width and the engine should run smoothly. This same problem may occur when any defective computer system component is replaced.

If the fuel delivery system is equipped with a cold start injector, make sure it gets cleaned along with the primary injectors.