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How To Test Fuel Injector Coils

When testing fuel injector coils, there are two primary methods: a resistance check and an insulation check. However, insulation testing applies only to piezoelectric injectors; it cannot be performed on GDI or Port injectors. More on that below.  This distinction is important, as an injector may pass a resistance check yet still be faulty.

Here is why

A coil can have proper internal winding resistance while still failing an insulation check. An insulation resistance test (like using a megger) checks for paths for electricity to leak to ground, rather than just checking the continuity of the winding itself. Insulation can break down due to physical damage, contaminants like moisture or oil, or thermal stress, even if the internal electrical resistance of the coil windings remains within normal limits.  

 

Do not use a megger to test Port or GDI fuel injectors.
Megger
 A megger, or megohmmeter, is an insulation resistance tester that applies a high-voltage DC charge to check for leakage in insulation, typically on large motors, cables, and high-voltage electrical equipment. Using a megger on a small, low-voltage automotive component like a fuel injector can damage its internal circuitry. Port and GDI Fuel injectors should be tested with a standard digital multimeter (DMM) only. 
A megger (or megohmmeter) tests the integrity of electrical insulation by applying a high DC voltage to the de-energized equipment and measuring the leakage current. It measures how much current leaks through the insulation at that high voltage. It calculates the resulting insulation resistance in megaohms to detect issues like moisture, dirt, or deterioration that could lead to electrical shock or equipment failure. A low or zero resistance reading indicates a problem. The higher the resistance reading in megohms (), the better the insulation is.
Multi Meter
The standard and safe way to test a port fuel injector is to measure its internal coil resistance using a multimeter.
Before you begin:
Testing procedure for Port Injectors:
  1. Locate and access the injectors. Disconnect the negative battery terminal for safety before starting.
  2. Disconnect the electrical connector from the fuel injector you want to test.
  3. Set your multimeter to the ohms (Ωcap omegaΩ) setting. A range of 200 or 2k ohms is usually appropriate.
  4. Touch the multimeter probes to the two metal pins inside the injector’s electrical connector.
  5. Note the resistance reading. Compare this value to the manufacturer’s specifications.
    • High-impedance injectors typically read between 12 and 16 ohms.
    • Low-impedance injectors typically read between 1 and 4 ohms.
  6. Compare all readings. Test each injector and compare the resistance readings. They should all be relatively close to one another, typically within 0.5 ohms.
  7. Identify a faulty injector. An injector with a reading that is significantly higher or lower than the others or an “open” (O.L.) reading is likely faulty and requires replacement.

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