TEST 9: Other Things That Can Cause A Misfire

How To Test The Coil Pack (Ford 3.0L, 3.8L, 4.0L, 4.2L)

So you've done all of the spark tests, and still your Ford (or Mercury or Mazda) six pack-er is still running rough (rough idle) and/or the misfire is still present. Well, here are a couple of suggestions that might help:

  1. Inspect the inside of the spark plug wire boots and the ceramic insulator of the spark plug for carbon tracks.
    • The photo above (the orange arrows) show what carbon tracks look like.
    • Replace the components as affected with carbon tracks.
  2. Engine compression test
    • One of the most overlooked diagnostic tests to find the root cause of misfire is the compression test.
    • You'll need an engine compression tester of course.
    • The engine compression readings between cylinders should not vary more 15%.
    • You can find a great step-by-step engine compression test article by clicking here: How To Do And Interpret An Engine Compression Test (Ford 3.0L, 3.8L) (at: troubleshootmyvehicle.com).
  3. Fuel injector test
    • The fastest way to test them is to measure them is by checking the resistance (Ohms) value of each one and comparing them to each other.
    • Any resistance that's not within the average of the others indicates the fuel injector is fried.
    • You can buy a specific fuel injector tester on line that activates by a predetermined pulse width and measuring the fuel pressure drop on a fuel pressure gauge.
    • You can find the test here: How To Test The Fuel Injectors (Ford 3.0L, 3.8L) (at: troubleshootmyvehicle.com).
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Ford Vehicles:

  • Aerostar 3.0L, 4.0L
    • 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997
  • Contour 2.5L
    • 1995, 1996, 1997, 1998, 1999, 2000
  • Explorer 4.0L
    • 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2006, 2007

Ford Vehicles:

  • E150, E250 4.2L
    • 1998, 1999, 2000, 2001, 2002, 2003
  • F150, F250 4.2L
    • 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2006, 2007, 2008

Ford Vehicles:

  • Mustang 3.8L, 4.0L
    • 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2006, 2007, 2008
  • Ranger 3.8L
    • 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2006, 2007, 2008

Ford Vehicles:

  • Taurus 3.0L
    • 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2006, 2007
  • Thunderbird 3.8L
    • 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997
  • Windstar 3.8L
    • 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003

Mazda Vehicles:

  • B3000 3.0L
    • 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2006, 2007

Mercury Vehicles:

  • Cougar 3.8L
    • 1989, 1990, 1991, 1992, 1993,1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002

Mercury Vehicles:

  • Mountaineer 4.0L
    • 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2006, 2007, 2008
  • Mystique 2.5L
    • 1995, 1996, 1997, 1998, 1999, 2000
  • Sable 3.0L
    • 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2006, 2007, 2008