How To Test The Fuel Injectors (4.2L Ford F150, E150, E250)

How To Test The Fuel Injectors (4.2L Ford F150, E150, E250)

Testing the fuel injectors on the 4.2L Ford V6 engine can seem like one very impossible task. This is due to the fact that they're located under the intake manifold plenum and you need to remove the upper intake manifold plenum to reach them.

If you're faced with having to test them, I have a couple of suggestions that'll help you get the job done.

In Spanish You can find this tutorial in Spanish here: Cómo Probar Los Inyectores De Combustible (4.2L Ford F150, E150, E250) (at:

Symptoms Of A Bad Fuel Injector

In a nutshell, a bad fuel injector will cause your 4.2L Ford F150 (E150, E250) to misfire at idle and while the vehicle is being accelerated.

This is due to the fact that each cylinder needs air, fuel and spark to produce power. So, when the fuel injector isn't injecting fuel (or not enough), that cylinder will misfire.

Here are some more specific symptoms:

  • Rough idle.
  • Lack of power.
  • Hesitation when you accelerate your 4.2L Ford pick up (van) down the road.
  • Since the 4.2L Ford pick up (van) is OBD II equipped, you'll see a misfire diagnostic trouble code (DTC):
    • P0300: Random Cylinder Misfire.
    • P0301: Cylinder #1 Misfire.
    • P0302: Cylinder #2 Misfire.
    • P0303: Cylinder #3 Misfire.
    • P0304: Cylinder #4 Misfire.
    • P0305: Cylinder #5 Misfire.
    • P0306: Cylinder #6 Misfire.

The fuel injectors, on your 4.2L Ford F150 (E150, E250) can fail in one of several ways:

  1. The fuel injector suffers an internal short-circuit or open-circuit problem. When this happens, fuel injector stops injecting fuel.
  2. The fuel injector becomes clogged and doesn't atomize the fuel correctly.
  3. It comes on and does not turn off (due to electrical issues). In other words: it does not pulse ON and OFF but stays on all of the time spraying a tremendous amount of fuel as soon as you turn the ignition key to the ON position.

Whether the fuel injector is fried internally or clogged, this tutorial will offer you some specific suggestions to help you narrow down the possible solution.

Where To Buy The Fuel Injector And Save

The following links will help you comparison shop for the fuel injector on your 4.2L Ford pick-up or van:

Not sure if the above fuel injectors fit your particular 4.2L Ford pick up (van)? Don't worry, once you click on the links and arrive on the site, they'll make sure it fits! If it doesn't, they'll find you the right one.

Checking The Injector's Internal Resistance

How To Test The Fuel Injectors (4.2L Ford F150, E150, E250)

If you're not sure you really do have a bad fuel injector and would like to know more about how to begin your troubleshooting, take a look at the following section first: How To Find The Bad Or Clogged Fuel Injector.

OK, as you're already aware, the upper intake manifold plenum has to be removed to access the fuel injectors. Although I don't include any R and R (remove and replace) info, I do have a few suggestions for you before you start. You can read them here: Precautions When Removing The Upper Intake Plenum.

NOTE: Don't have a multimeter or need to upgrade yours? Check out my recommendation: Buying A Digital Multimeter For Automotive Diagnostic Testing.

Alright, here are the steps:

  1. 1

    After removing the intake manifold's plenum, disconnect the fuel injectors from their harness connectors.

    NOTE: The illustration above will help you identify the cylinder # the fuel injector belongs to.

  2. 2

    Place your multimeter in Ohms (Ω) mode and:

    Measure the resistance of the fuel injector across its two male spade terminals with the multimeter test leads (see the illustration above).

  3. 3

    Write down the resistance value that your multimeter records for the specific fuel injector you're testing. The illustration above will help you identify the cylinder # the fuel injector belongs to.

  4. 4

    Repeat steps 1 through 3 on the remaining fuel injectors.

    NOTE: The 4.2L Ford pick up (van) fuel injector factory manual resistance specification is approximately: 8.5 to 15.5 Ohms.

Let's find out what your specific multimeter test results mean:

CASE 1: Your multimeter reports all fuel injector resistances are within specification. This tells you that your 4.2L Ford's fuel injectors are OK. Specifically, that none are shorted or open internally.

Here's why: If any one of the fuel injectors were shorted or open internally, the fuel injector would have registered a radically different resistance value on your multimeter. Since the resistance values for all 6 were uniform, this test result tells you that they are not defective.

CASE 2: Your multimeter reports a fuel injector with a completely different resistance value. This indicates that the fuel injector is bad. Replace the fuel injector.

Ford Vehicles:

  • E150 4.2L
    • 1999, 2000, 2001, 2002, 2003
  • E250 4.2L
    • 1999, 2000, 2001, 2002, 2003, 2004
  • F150 4.2L
    • 1999, 2000, 2001, 2002, 2003, 2004