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:
- 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.
- 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).
- Fuel injector test
- There are several methods to test them which are beyond the scope of this article but...
- 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 really saved the day, buy me a beer!