The Fuel Injector Test

How To Test The Fuel Injectors (5.0L Engine, 5.8L Engine)

Once you've located the ‘dead’ cylinder and are sure that the problem isn't caused by an ignition system issue or low compression, the next step is to test the resistance of the fuel injector (that belongs to the ‘dead’ cylinder).

If the fuel injector (that feeds the ‘dead’ cylinder) is under the intake manifold plenum, you're gonna' have to remove it to get to it. If you haven't removed it yet, take a look at the following section: Important Tips. Alright, enough talking, here's the test:

  1. 1

    Remove the intake plenum (if applicable).

    1. IMPORTANT: After removing the intake manifold's plenum, place clean rags in the open intake runners.
    2. Disconnect all 8 fuel injectors from their electrical connectors.
    3. You don't have to test them all, but if you do have the intake manifold plenum off of the intake manifold, you might as well.
  2. 2

    Place your multimeter in Ohms mode and probe the metal male spade terminals inside the fuel injector with the multimeter test leads. What you're doing is measuring the resistance of the fuel injector.

  3. 3

    Measure the resistance of the same fuel injectors several times so that you can be sure of your multimeter's Ohms result.

    1. When done, write this Ohms value down and record the number of the cylinder that fuel injector belongs to, too.
  4. 4

    Repeat test steps on the remaining fuel injectors.

Interpreting The Results Of The Fuel Injector Test

Alright, let's interpret your results. Choose from one of the following CASES:

CASE 1: All of the multimeter resistance values are nearly identical. This result tells you that the fuel injectors are good and are not causing the misfire condition or rough idle condition.

If you did have one bad fuel injector in the whole bunch, you would get a drastically different Ohms value in one of them. For example, if 5 of the 6 measured 11.5 to 11.9 Ohms and the sixth one measured 4 Ohms. Well, the one measuring the 4 Ohms is the one that's fried.

CASE 2: One of the fuel injector multimeter resistance values is radically different. Retest that one fuel injector once again. If the fuel injector registers the same Ohms value as before, then that fuel injector is bad.

Important Tips

If you do have to remove the intake manifold's plenum, to get to the fuel injectors underneath it, you need to keep in mind several important things:

  1. 1

    Be careful that no foreign object, like a bolt, a nut, or any metal piece/part, falls into the open manifold port runners or you run the risk of engine damage if you start the vehicle.

  2. 2

    Once the plenum has been removed, place a clean rag or rags on the open intake runners. This will keep things from falling into them.

  3. 3

    As you're removing bolts, nuts and stuff from the intake plenum to remove it, place them in a container and away from the engine compartment.

Anything falls into the open intake runners, without you knowing it, and the engine is started, you are going to be in a big world of hurt!

If this happens, the only way to remove the object is to remove the cylinder head. So be alert and be careful. Removing the plenum is not an out of this world thing that no one can do or that should not be done, you just have to be careful (heck, even just crossing the street has risks!).

Thank You For Your Donation

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Ford Vehicles:

  • Bronco 5.0L, 5.8L
    • 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996
  • Crown Victoria 5.0L
    • 1989, 1990, 1991
  • E150, E250, E350 5.0L, 5.8L
    • 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996

Ford Vehicles:

  • F150, F250, F350 5.0L, 5.8L
    • 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997
  • Mustang 5.0L
    • 1988, 1989, 1990, 1991, 1992, 1993
  • Thunderbird 5.0L
    • 1988, 1989, 1990

Lincoln Vehicles:

  • Continental
    • 1988, 1989, 1990
  • Mark VII
    • 1988, 1989, 1990, 1991, 1992
  • Town Car
    • 1988, 1989, 1990

Mercury Vehicles:

  • Cougar 5.0L
    • 1988, 1989, 1990

Mercury Vehicles:

  • Grand Marquis 5.0L
    • 1988, 1989, 1990, 1991