I started having problems with misfires on cylinder 3 a couple months ago that I outlined here. My main question with that post was which AC-Delco coil pack to buy. As I mentioned there, I ended up buying a Delphi. Well, it failed about a month later. Had to replace it with a Duralast from Autozone because I needed it fixed right away - couldn't wait for Amazon. Decided to pull the plug before installing the new coil pack. The electrode was nearly gone. Looked like it might have broken off. Gap was about 0.070". Plugs are all 41-103's. Thought the plug may have been the problem all along. Tried just replacing the plug (with a 41-103, of course) and putting the Delphi coil back in. No luck - still misfiring, proving the coil pack was dead. Misfire went away after replacing the plug and installing the Duralast coil pack.
Fast forward to last Friday. Was headed out of town about 120 miles with the cargo area piled up to the roof and pulling two snowmobiles. Starts misfiring again. Luckily, I was close to a relative's house. Stopped there and hooked up Torque (I've learned not to leave the house without Torque and my OBDII transmitter). Misfiring on cylinder 6. Ran to the closest Autozone and got another Duralast coil and spark plug. Electrode was nearly gone - same as the plug on cylinder 3. Replaced both, misfire gone, continued on trip. Was driving home Sunday after a weekend of snowmobiling, starts misfiring again. This time cylinder 4. Got home and replaced the remaining four plugs and coil packs. All six plugs looked about the same as the attached picture. Electrode nearly gone - gap of about 0.070".
Plugs were less than a year old - about 20,000 miles on them. Like I said, they were AC Delco 41-103's. I thought those things were supposed to last for 100,000 miles (the first set I put in did). Defective?
Could the worn out plugs have been causing the coil pack failures? Increased gap increased the voltage requirement for the spark to jump the air gap, resulting in coil pack failures? Chicken or egg - were the plugs killing the coil packs or did I just reach the mean time of failure for OEM coil packs? Truck is an '03 with 198,000 miles.
Fast forward to last Friday. Was headed out of town about 120 miles with the cargo area piled up to the roof and pulling two snowmobiles. Starts misfiring again. Luckily, I was close to a relative's house. Stopped there and hooked up Torque (I've learned not to leave the house without Torque and my OBDII transmitter). Misfiring on cylinder 6. Ran to the closest Autozone and got another Duralast coil and spark plug. Electrode was nearly gone - same as the plug on cylinder 3. Replaced both, misfire gone, continued on trip. Was driving home Sunday after a weekend of snowmobiling, starts misfiring again. This time cylinder 4. Got home and replaced the remaining four plugs and coil packs. All six plugs looked about the same as the attached picture. Electrode nearly gone - gap of about 0.070".
Plugs were less than a year old - about 20,000 miles on them. Like I said, they were AC Delco 41-103's. I thought those things were supposed to last for 100,000 miles (the first set I put in did). Defective?
Could the worn out plugs have been causing the coil pack failures? Increased gap increased the voltage requirement for the spark to jump the air gap, resulting in coil pack failures? Chicken or egg - were the plugs killing the coil packs or did I just reach the mean time of failure for OEM coil packs? Truck is an '03 with 198,000 miles.