How Can I Test The Misfire?

How To Test Misfire Codes (4.0L Ford Explorer, Ranger, Aerostar, Mercury Mountaineer)

Troubleshooting a misfire condition on your 4.0L equipped Ford Explorer (Ranger, Aerostar, or Mountaineer) can seem quite intimidating but it shouldn't be. As I mentioned in the previous page, the key to diagnosing the cause of the misfire condition (or code) is to find out what is missing from the misfiring cylinder.

The misfiring cylinder will have one of three things missing: spark, fuel, or air (compression). It's as simple as this.

In this section, I'll show you a specific diagnostic strategy that'll help you find the component that's causing the problem.

STEP 1: Identify the dead cylinder. This is the most important first test that will save you a lot of time and frustration down the road by narrowing down and focusing your misfire diagnostic.

Since the vehicles covered by this tutorial are OBD II equipped, identifying the dead (misfiring) cylinder usually means connecting a scan tool and checking for misfire codes (P0301, P0302, P0303, P0304, P0305, or P0306). Then by matching the misfire code to its engine cylinder using an illustration of the engine cylinders.

STEP 2: Test the ignition system. Once you know which of the 6 cylinders is the one that's dead... the next step is to make sure that cylinder is getting spark (with a spark tester).

This is what I recommend:

  1. Check that the spark plug wire is delivering spark with a spark tester.
    1. Testing for spark with a spark tester is the most important first test since you'll know right away if the misfire is due to a lack of spark.
  2. If you got spark from your spark tester (from the cylinder the misfire code is accusing of misfiring), the next step is to remove the spark plug or spark plugs (of the affected cylinders) and check them for wear and tear, carbon tracks, anti-freeze, etc.
  3. If you get no spark, then the next step is to check for spark directly on the ignition coil pack tower.
  4. You can find all of these ignition system tests here:
    1. How To Test The Coil Pack (Ford 3.0L, 3.8L, 4.0L, 4.2L) (at: easyautodiagnostics.com).

STEP 3: Test the fuel injector(s). If everything checks out with the ignition system, then your next step is to eliminate the fuel injectors as the cause of the misfire.

This is what I recommend you do:

  1. Resistance test the fuel injector that belongs to the ‘dead’ cylinder (along with at least 2 others).
  2. Do a noid light test of each one to make sure the PCM is pulsing them (activating them).
  3. You can find the fuel injector tests here:
    1. How To Test The Fuel Injectors (Ford 4.0L).

STEP 4: Test the compression of the engine cylinder(s). Other tests that should be done, if the ignition system and fuel injectors check out OK are:

  1. Engine compression test.
  2. Checking for vacuum leaks.
  3. You can find the engine compression test here:
    1. How To Test Engine Compression (Ford 4.0L).

The above list of steps may seem/sound like troubleshooting a misfire is a complicated thing but it really isn't. Remember, the key to finding the exact cause of the misfire is to find out what is missing from the misfiring cylinder and depending on your wrenching experience, this is something you can do yourself.

What Tools Do I Need To Test The Misfire Code(s)?

Finding the exact cause of the misfire codes or misfire condition is possible... with the proper tools. Without them, you won't be able to diagnose/troubleshoot those issues on your 4.0L equipped Explorer (Ranger, Aerostar, or Mountaineer).

Depending on what the root cause of the misfire is, you may need several tools. Most of these you can buy online, none of these will break the bank and I'll make some recommendations on them. Here's a guide to some of the basic tools that can be and are used:

  1. Ignition System Tests:
    1. Spark tester.
    2. Multimeter.
    3. Test light.
  2. Fuel System Tests:
    1. Noid light.
    2. Fuel pressure gauge.
    3. Multimeter.
  3. Engine Mechanical Tests:
    1. Compression tester.

Now of course, you'll also need basic hand tools like: screw-drivers, ratchet wrenches, sockets, etc. You'll also need a generic scan tool to retrieve the diagnostic trouble codes (DTC's) from the computer's memory.

Keep in mind that using the right tool for the job will save you time, frustration, and /or keep you from damaging the component that you're testing.

More Ford 4.0L Tutorials

You can find a complete list of 4.0L Ford troubleshooting tutorials here: Ford 4.0L Index Of Articles.

Here's a sample of the tutorials you'll find in the index:

  1. How To Test The Fuel Pump (Ford 4.0L Aerostar, Ranger, Explorer).
  2. How To Test Engine Compression (Ford 4.0L).
  3. How To Troubleshoot A No Start (Ford 4.0L).
  4. How To Test The Fuel Injectors (Ford 4.0L).
  5. How To Test The Ford EGR Valve EGR Vacuum Solenoid, DPFE Sensor (at: easyautodiagnostics.com).
  6. How To Test The Coil Pack (Ford 3.0L, 3.8L, 4.0L, 4.2L) (at: easyautodiagnostics.com).
Thank You For Your Donation

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Ford Vehicles:

  • Aerostar 4.0L
    • 1995, 1996, 1997
  • Explorer 4.0L
    • 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003
  • Ranger 4.0L
    • 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003

Mercury Vehicles:

  • Mountaineer 4.0L
    • 1997, 1998, 1999, 2000, 2001, 2002, 2003