How to Troubleshoot Fuel Injectors When They are not Pulsing

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How to Troubleshoot Fuel Injectors When They are not Pulsing
A multimeter allows you to test voltage and resistance. (Polka Dot Images/Polka Dot/Getty Images)

Fuel injectors are connected to pressurised fuel lines. The fuel injector controls the injection of fuel into the combustion chamber through an electronic pulse. The incoming electricity charges a solenoid that briefly opens a valve. When the valve is open, the pressurised fuel passes through the fuel injector into the combustion chamber. A single charge of the solenoid and the subsequent opening and closing of the valve is what is considered the "pulsing" of the fuel injector. Electrical failure, electrical shorts and bad fuel injectors may all result in pulse failure.

Skill level:
Moderate

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Things you need

  • Multimeter
  • Small wire brush
  • Dielectric grease
  • Screwdriver

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Instructions

    Injector Lead Testing

  1. 1

    Turn the ignition key to "Start," but do not start the engine.

  2. 2

    Set your multimeter to measure volts.

  3. 3

    Disconnect the electrical plug from the non-pulsing fuel injector. Pull the electrical plug and wired lead away from the fuel injector to allow access to the metal tabs in the plug.

  4. 4

    Touch the red and black multimeter leads to each side of the electrical plug. You can place either lead on either side of the plug.

  5. 5

    Measure the voltage being passed through the lead. The multimeter should display approximately 12 volts. If the lead is not producing the correct voltage, and the other leads are producing correct voltage, replace the electrical lead.

    Electrical Plug Corrosion

  1. 1

    Pull the electrical plug from the fuel injector.

  2. 2

    Inspect the metal connections on both the electrical plug and the fuel injector. The electrical plug and fuel injector terminal should both be free of corrosion and moisture.

  3. 3

    Use a small wire brush to clean the terminal contacts, if corrosion is found.

  4. 4

    Apply a small amount of dielectric grease to the terminal of the fuel injector.

  5. 5

    Reconnect the electric plug to the fuel injector. Start the engine and test for a pulse.

    Fuel Injector Pulse Testing

  1. 1

    Start the engine.

  2. 2

    Touch the tip of a screwdriver to the fuel injector. Press your ear to the handle of the screwdriver.

  3. 3

    Listen for a clicking sound through the screwdriver. The solenoid and valve operation will create an audible click that can be heard through the screwdriver when the fuel injector is pulsing. On some fuel injectors, you can feel the clicking as soon as you touch the screwdriver to the injector.

    Short Circuit Testing

  1. 1

    Disconnect all fuel injector leads from the injectors.

  2. 2

    Set the multimeter to measure volts. Connect the black multimeter lead to the vehicle battery positive terminal. Connect the red multimeter lead to the electrical plug of one of the fuel injector leads.

  3. 3

    Have an assistant turn the ignition key to attempt to start the engine.

  4. 4

    Measure the incoming voltage. The voltage will alternate between 12 volts and 0 volts.

  5. 5

    Connect one of the other electrical plugs to the respective fuel injector and repeat Steps Three and Four. You will only test the original lead. This test helps you determine what fuel injector is creating a short circuit. Continue connecting fuel injectors and retesting the original lead until all fuel injectors are tested. A short circuit will cause non-alternation of current on the fuel injector system. Lack of current pulsing results in non-pulse of the injectors.

  6. 6

    Replace any fuel injector that results in a short circuit of the electrical leads.

  7. 7

    To test the final fuel injector, connect it and pull a prior connected electrical plug. Repeat the voltage test on the newly disconnected plug to confirm the final injector is not short-circuiting the injection system.

    Resistance Testing

  1. 1

    Disconnect the fuel injector electrical plugs from each of the fuel injectors.

  2. 2

    Set the multimeter to measure ohms.

  3. 3

    Connect the red and black multimeter leads to each side of the terminal end of the fuel injector. Either coloured lead can be connected to either side of the terminal.

  4. 4

    Measure the ohms, or resistance, of the fuel injector. Write down the measurement.

  5. 5

    Repeat Steps Three and Four on all of the remaining fuel injectors.

  6. 6

    Compare all the resistance measurements. All of the ohms measurements should be roughly the same. Any fuel injector with a significantly higher or lower resistance measurement is failing or has failed.

  7. 7

    Replace failed fuel injectors.

Tips and warnings

  • Apply dielectric grease to all fuel injector connections. The grease will protect the terminals from corrosion and short circuiting.
  • Repair all fuel injector fuel leaks before performing electrical tests. Leaking fuel from the fuel rails or injectors may be ignited by small sparks from the electrical tests.

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