What is causing the engine to misfire on cylinders two and six?

Hello,

So, you just have to use a process of elimination. Unfortunately, the codes just send you in a general direction. Spark plugs are the most likely cause. I would start by pulling the plugs from the cylinders you already know are misfiring, number 2 and 6.

Also make sure the hole and top of valve cover is clean before starting. Use a vacuum of compressed air to get all of the crud out of the way. You don’t want any of this getting in your engine.

While you have the coils off take a look at them for signs of something called carbon tracking. (I have added a picture as an example) If you see it therefore your cylinders are misfiring. It’s not that likely but remember we are eliminating possibilities, so we want to check it and rule it out.

Electricity is always going to go for the shortest path to ground. Which should be provided through the tip of the plug, but if not, it will find a new direction. Some causes of this could be the plug has excessive resistance or a worn-out plug boot.

If the boots look too worn or are hardened or splitting, you will need to replace the boots. These are fine to get from the parts store. Depending on the design, you might need to replace the entire coil.

When you put it back together use die electric grease on the boot. This grease is non-conductive and will help “seal” the electricity in the boot.

I also added a chart so that you can look at your plugs and get an idea of why they are misfiring. If you don’t correct the original condition, then the issue will just return.

I always recommend using OEM plugs, in your case A/C-Delco is going to be perfect. Go to the dealer and give them your 17-digit VIN so that they can find exactly what goes in your vehicle. This will save headaches and problems down the road. The other good thing is they come pre-gapped.
*However, just because a spark plug is pre-gapped, don’t assume it is correct, always check. *

It is always good practice to check with a feeler gauge. I have included a picture of one as well as the spec for the gap. It should have a light drag, not too much, when you check the gap. Do not use the circular gap tools as they will damage the tip of the plug.

Spark plugs should be torqued. The cylinder heads they screw into are aluminum and just a little over tightening can stretch the threads for the spark plug holes.

However, everyone doesn’t have a torque wrench, so I advise if you don’t to use a 3/8” ratchet with just a regular 7” or so handle. Don’t use anything long. Then gently snug them up with that. You should be able to feel when you get to the right spot. If it gets loose again, then you went too far.

If you have any other questions at all just reply to this post. We are here to help any way we can.