This 2002 Isuzu Rodeo with a 3.2 liter V6 engine came in with a flashing check engine light and a complaint of skipping. There was only a general misfire code P0300. I hate general misfire codes. I cleared the code and ran the vehicle under load to induce the misfire. After a few minutes the light was back on and there was a code P0302 for a specific misfire on cylinder number 2. I removed the #2 coil assembly and this is what I found. The spark plug boot and tube were heavily coated in soot.
The spark plug itself was a mess as well. The customer had installed new spark plugs about four months ago.
Before removing the spark plug I used a shop vacuum to remove as much soot as possible. Then a combination of wiping the tube with a rag wrapped around a screwdriver blade,vacuuming and blowing the hole out with an air hose. After I removed as much soot as possible, I removed the spark plug and started cleaning all over again.
In case you are wondering the number two cylinder is the front cylinder on the driver’s bank of the engine.
I had to remove build up from the coil tip as well. I used a wire brush and a rag to clean the coil.
Here are some of the tune up basics that I have learned over the years. Dielectric grease is good to put inside the spark plug boots but only a small amount. The amount on the tip of my screwdriver blade is about twice as much as is needed. I start with that much and make sure that about half of it comes back out after spreading a light film inside the boot. The dielectric grease is used to make sure the boot slide on and off of the spark plug with reduced effort. Too much grease and the spark will cut a carbon track down the side of the plug. This will result in a misfire and the need for more parts.
The two most important things I use in spark plug replacement are a spark plug gap checker and a torque wrench. Not all spark plugs arrive properly gapped and improper torquing of the spark plug will result in a loose spark plug as wee had in this repair article or damaged threads in the cylinder head. Because of space problems a torque wrench cannot be used for every spark plug. Doing as many as possible, on a particular vehicle, will give you a feel of what the correct torque is though. The correct torque on this vehicle was 18 ft lbs. This torque is needed to compress the crush gasket on the spark plug. This gasket provides the seal against combustion gasses.