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

TEST 9: Other Things That Can Cause A Misfire

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).

If this info saved the day, buy me a beer!