I just wanted some thoughts on my spark plugs. I've been getting the p0300 misfire code (along with a P0455 code, EVAP Leak), so I took a look at the plugs. I just bought the car used a short time ago, so not sure how many miles are on them but l will be replacing them along with the wires to (hopefully) address the misfire. They do not appear to be oil fouled to me. But there was clean oil on the base of the threads of the 6 I pulled. One had a little more oil toward the top. Car doesn't seem to be burning oil. It does have an oil leak that I am also trying to address but appears to be in the bottom half. I don't see oil around the valve covers.

My questions are:

1. Do these look oil fouled?
2. Is this enough oil to be the cause of the misfire code?
3. Does it look like I have a major problem based on their condition?

Car is a 2008 LS3 C6 base with 97,000 miles on it, headers, exhaust, tune and no cats. Upper O2 sensors were recently changed.

Thanks for any input!




This one was the worst

 

Did you ever figure out what caused those codes? I'm experiencing the same codes on a 2008 C6 LS3 with 120k miles.

 

TL,DR: New Evap canister fixed the 0455 code. Fresh tune fixed the 0300 misfire code.

For me, it got worse before it got better. The 0455 code is the evap canister. In theory, a cheap and easy fix. It's in a tight spot above one of the gas tanks but doable if you can get under the car. But when I got it in the air to change it out, I realized I also had the fuel leak issue. I was so upset, I didn't bother to change the canister. So, I found a shop to replace both fuel pumps and level sensors. They changed the EVAP canister while they had it a part. The 0455 code was gone but the 0300 misfire remained. After 2 regular shops blamed the tune, I finally found a speed shop with a tuner to look at it. And sure enough, a fresh tune got rid of the misfire. All in all, $3500 for the fuel pump work and a tune. But the car has no codes and runs great. Still loving it.

Again, the EVAP canister isn't a hard DIY job. As for the misfire, mine was probably a unique case. It logged 0300 but I never felt it misfiring. It always ran strong. From reading various threads, more common misfire causes are bad or loose spark plugs, bad or loose ignition wires, bad injectors and bad crankshaft position sensor. There are others of course, including bad internals. But those seemed to be the most common on here. Hopefully, it'll be an easy fix for you. Good luck.