Fuel Injector Resistance Test (1997-2000 4.0L Ford Ranger And Mazda B4000)

How To Test The Fuel Injectors (1997, 1998, 1999, 2000 4.0L Ford Ranger And Mazda B4000)

As you're probably already aware, the 4.0L V6 engine in your Ford Ranger (Mazda B4000) has three of its six fuel injectors under the intake manifold plenum. The location of these six fuel injectors makes testing them a challenge.

In this tutorial, I'll share my fuel injector diagnostic strategy. I'm confident it'll help you find out if you've got a bad fuel injector.

NOTE: You can find the 1997-2000 4.0L Ford Explorer and Mercury Mountaineer fuel injector test here:

APPLIES TO: This tutorial applies to the following vehicles:

  • 4.0L V6 Ford Ranger: 1997, 1998, 1999, 2000.
  • 4.0L V6 Mazda B4000: 1997, 1998, 1999, 2000.

The fuel injector resistance test tutorial for the 1990-1996 4.0L Ford Ranger (Mazda B4000) is here:

Fuel Injector Resistance Specifications

Engine Ohms
4.0L Ranger 11-18 Ohms
4.0L B4000 11-18 Ohms

The Fuel Injector Resistance Test

Testing The Resistance Of The Fuel Injector With A Multimeter (1997, 1998, 1999, 2000 4.0L Ford Ranger And Mazda B4000)

When a fuel injector suffers an internal short-circuit or open-circuit problem, it'll stop injecting fuel into its cylinder.

You and I can determine if this has happened by checking the fuel injector's resistance and comparing it to the factory specification.

Before we start, and if you haven't already, take a look at the following section before testing the fuel injectors:

You'll need a multimeter to test the fuel injector resistance. If you don't have one, check out my recommendations here: Buying A Digital Multimeter For Automotive Diagnostic Testing.

These are the test steps:

  1. 1

    Removing the intake manifold's plenum.

    NOTE: Cover the open intake runners when clean shop towels.

    See this section: Important Precautions When Removing The Intake Manifold Plenum.

  2. 2

    Disconnect all six fuel injectors from their electrical connectors.

  3. 3

    Place your multimeter in Ohms mode.

  4. 4

    Probe the metal male spade terminals inside the fuel injector with the multimeter test leads.

  5. 5

    Your multimeter should register a resistance between 11-18 Ohms.

  6. 6

    Repeat test steps on the remaining fuel injectors.

Let's interpret your test results:

CASE 1: The resistance of each individual fuel injector is within specification. This is the correct and expected test result.

This result confirms the fuel injectors do not have an internal short-circuit or open-circuit problem.

CASE 2: One of the fuel injector resistance values is not within specification. This fuel injector has an internal short-circuit or open-circuit problem. Replace the fuel injector.

Fuel Injector Troubleshooting Strategy

The following fuel injector troubleshooting strategy has helped me pinpoint the faulty fuel injector causing a misfire or rough idle problem.

And if a bad fuel injector wasn't causing the misfire or rough idle condition, it nailed down the real cause of the problem.

These are the steps:

PART 1: Identify The Dead Cylinder.

Identifying the 'dead' cylinder is the critical first step of this fuel injector diagnostic strategy.

You can pinpoint the 'dead' cylinder by performing a cylinder balance test.

The biggest benefit of the cylinder balance test is that it'll help determine if the 'dead' cylinder's fuel injector is located underneath the intake manifold plenum.

NOTE: Even if you have a cylinder misfire diagnostic trouble code, do the cylinder balance test to make sure you've identified the correct cylinder.

PART 2: Make Sure The Dead Cylinder Is Getting Spark.

After you've identified the 'dead' cylinder, your next step is to make sure its spark plug wire delivers spark to its spark plug.

You must perform the spark test with a dedicated spark tester. Any spark test method that does not involve a spark tester will only have you chasing ghosts (and wasting time and money).

You'll also need to:

  • Check the spark plug for any apparent damage.
  • Check the spark plug for excessive wear.
  • Check the spark plug electrodes are not blocked with carbon.
  • Check the spark plug's air gap.
  • Check the spark plug, and the spark plug wire does not have carbon tracks.
  • Check the spark plug wire isn't missing the metal connector that connects to the spark plug.

If the 'dead' cylinder isn't getting spark, you've found the source of the misfire (rough idle), you don't need to test the fuel injectors.

If the 'dead' cylinder is getting spark and the spark plug and spark plug wire are OK, the next step is checking the 'dead' cylinder's compression.

PART 3: Make Sure The Dead Cylinder Has Compression.

If the ignition system is not causing the 'dead' cylinder issue, your next step is to make sure the 'dead' cylinder produces enough compression to start and complete the air/fuel mixture's combustion process.

Now, you don't need to test all six cylinders. But for the accuracy of your diagnostic, you should test all six.

You can find the compression test explained in detail here:

If the 'dead' cylinder's compression value is 15% lower than the highest compression reading your compression test has given you, then you've found the cause of the misfire (rough idle) issue, and you don't need to test the fuel injectors.

If the 'dead' cylinder's compression value is within a normal range, your next step is to test the fuel injectors.

PART 4: Test The Fuel Injectors.

If you've reached this point, you now know that:

  • The ignition system is not behind the problem.
  • The cylinder's compression is not behind the problem.

If the 'dead' cylinder's fuel injector is underneath the intake manifold plenum, you can now make plans to remove it and resistance test the fuel injector.

Ford Vehicles:

  • Ranger 4.0L
    • 1990, 1991, 1992, 1993, 1994, 1995, 1996

Mazda Vehicles:

  • B4000 4.0L
    • 1994, 1995, 1996