How to Test a BAD Fuel Injector (1997-2002 4.6L F150)

Testing the fuel injectors on your Ford F 150 with a 4.6L engine is not hard. If you have a multimeter, this tutorial will help you to find out if any one of those 8 fuel injectors are fried.

You're going to be surprised just how easy it is to test a fuel injectors on these 4.6L Ford engines.

Contents of this article at a quick glance:

  1. Symptoms of Bad Fuel Injector.
  2. Checking the Injector's Internal Resistance.
  3. How to Find the BAD or Clogged Fuel Injector.
  4. Where to Buy the Fuel Injector and Save.

NOTE: This tutorial applies to several different years of F150, F250, E150, E250, and Expedition models with a 4.6L V8 engine. To see if your specific pickup, van or SUV is covered by this tutorial, check the Applies To: box on the right column.

Symptoms of Bad Fuel Injector

You're probably already aware that each cylinder needs three things to produce power. These are: air, fuel, and spark. If any one of these is missing from any one cylinder, when the engine is running, that cylinder will misfire.

Since the fuel injectors are the ones responsible for getting the fuel into the engine cylinders. If any one of them gets clogged or stops working, your 4.6L Ford engine's performance is gonna' suffer.

Here are the most common symptoms you'll see when a one fails:

  1. Rough idle.
  2. Lack of power.
  3. Hesitation when you accelerate your pickup (van or SUV) down the road.
  4. Misfire trouble codes:
    1. P0300: Random Cylinder Misfire.
    2. P0301: Cylinder #1 Misfire.
    3. P0302: Cylinder #2 Misfire.
    4. P0303: Cylinder #3 Misfire.
    5. P0304: Cylinder #4 Misfire.
    6. P0305: Cylinder #5 Misfire.
    7. P0306: Cylinder #6 Misfire.
    8. P0307: Cylinder #7 Misfire.
    9. P0308: Cylinder #8 Misfire.

Fuel injectors usually fail in one of two ways. They either become clogged and don't inject enough fuel, or their internal coil winding shorts out and stops injecting fuel completely.

The test I'm gonna' show you deals primarily with shorted fuel injector coil windings. But, I'll also offer you a specific diagnostic strategy to find a clogged fuel injector (in the next page, heading: How to Find the BAD or Clogged Fuel Injector)

Checking the Injector's Internal Resistance

How to Test a BAD Fuel Injector (1997-2002 4.6L F150)

When a fuel injector stops injecting fuel completely, it's usually because its internal coil winding has become shorted or has an open circuit. You and I can easily check this by doing a simple multimeter resistance test. The cool thing about the 4.6L Ford engine is that its fuel injectors are pretty easy to get to.

So, we're gonna' start off by checking the internal resistance of all 8 fuel injectors. The resistance specification is 11 to 18 Ohms.

Before you start, let me tell you that broken fuel injector connectors are one of the most common problems with the 4.6L Ford engine. To be a bit more specific: it's the plastic locking tabs of the connector that break. So before you start, take a look at all of the fuel injector connectors to see if you have any that have broken locking tabs. If you do find any broken fuel injector connectors, there's a good chance that you've found the problem that's causing the fuel injector not to work (since the broken locking times will cause the connector to make a false contact with a fuel injector).

NOTE: Your fuel injector resistance test should be done with your Ford vehicle's engine cold. If the engine has been running for any extended length of time, let it cool down completely.

These are the test steps:

  1. 1

    Disconnect the fuel injectors from their engine wiring harness connectors.

    NOTE: To identify which cylinder the fuel injector belongs to, see the above illustration with the cylinder # IDs.

  2. 2

    Set your multimeter to 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 fuel injector resistance specification is: 11 to 18 Ohms.

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

CASE 1: All 8 fuel injector resistance values are within specification (11 to 18 Ohms). This is the expected and correct test result and tells you that none are shorted or open internally.

If you suspect that you have a clogged fuel injector, which a resistance test won't find, take a look at the following section: How to Find the BAD or Clogged Fuel Injector.

CASE 2: One of the fuel injectors registered a resistance value NOT within the specification. This indicates that the fuel injector is BAD. Replace the fuel injector.