Since the customer had already told us that he had already replaced the spark plugs, here was the troubleshooting plan:

  1. Test the spark output of the ignition coil for that particular cylinder with my HEI Spark Tester (learn more about this tool here: The HEI Spark Tester (The Best Spark Tester On The Market)).
  2. Remove the spark plug wire from its tube to:
    • Look for a carbon track on the inside of the spark plug cable boot.
    • See if the valve cover spark plug tube seals are leaking oil into the spark plug tube well.
  3. Remove the spark plug(s) and:
    • Check that it (they) was (were) torqued correctly.
    • That the customer did not break or crack the ceramic insulator (porcelain part) of the spark plug as he installed it (a very common problem).
    • Check for carbon tracking on the ceramic insulator part of the spark plug.
    • Check engine compression.
  1. Test the fuel injector circuit for the #2 cylinder with a Noid light.
    • If no injector pulse, check all of those circuits.

Now the above list can go on and on till the problem is found. You have to start somewhere, and this is where I usually start and go from there.

Second Step In Testing An Ignition Misfire: Spark Test

Making Sure The Spark Plug Wire Is Firing Off Spark With A Spark Tester. Carbon Tracks Are A Common Cause Of Ignition Misfires

After planning the strategy in my head, it was now time to execute the plan! Now, the cool thing about testing a misfire condition (on any car) is that the tests are easy and you don't need any expensive tools! The very first thing I needed to do was to test each spark plug wire for spark and this is how I did it:

I pulled out the cylinder #2 spark plug wire. The boot was not soaked in oil. I peered down the spark plug tube and it too was dry of oil. Oil leaking into the spark plug tube and onto the spark plug is a common cause of ignition misfires. If the spark plug tube had been full of oil, I would have stopped here.

Next I hooked up my HEI spark tester to it (as you can see in the photo above). I got in the car and cranked it up. As it cranked and started I could here an audible spark noise coming from the spark tester. I did this for every single spark plug wire.

Normally I would ask someone to help me to crank the car as I eye-ball the HEI spark tester, but this morning I had to do it solo. Now, the good thing about the HEI spark tester is that you can audibly hear the spark jumping across the air gap. This loud ‘cracking’ sound is loud enough to hear from inside the passenger compartment.

Now, since the cylinder #2 spark plug wire sparked, I then tested the three remaining spark plug wires for spark. It's important to test every wire for spark with the spark tester. By testing all of the wires I'm making sure I'm eliminating as many possible components as possible. Not taking the time to completely follow through with a complete diagnostic to tie up any and all loose ends will always come back to bite you in the butt.

Carbon Track On The Spark Plug

Well, the other three spark plug wires sparked. Since there was spark on every single spark plug wire, I now knew that the ignition coil pack was functioning correctly. The coil pack could completely be eliminated as the source of the misfire. This is the benefit of testing with this HEI spark tester. Over the years I have tried other spark testers and none have given me the guaranteed results this one does. I highly recommend it to you.

What next? I pulled out my trusty flashlight and looked inside the spark plug boot itself. To my pleasant surprise I could very clearly see a carbon track on the inside. I then removed the spark plug and lo and behold -it too had a very visible carbon track! The photo on the right is the very same spark plug I'm describing.

In the next page, I have a beautiful picture of the carbon track inside the spark plug boot. Lets go see it.