Hey guys,

Yesterday I changed spark plugs for 2008 G37s Coupe 6MT at 105,900 miles. And after that the car misfire when idling. So went to Autozone, they gave me 2 codes, P0306 & P0300. (cylinder 6 misfire & multiple misfiring). I went to O'reilly's Auto after that and the code they gave me was a cylinder 6 misfire.

My friends and I took apart all 6 spark plugs to look at them. The coil packs seems fine, but there were some oil inside where the spark plug was sitting on the last spark plug on the driver's side.

Can anyone tells me what is going on? Some says piston rings are worn, and some says the valve cover gasket needs to be replaced. There was a SES light on when the misfiring started happening, then it went away but misfire still occurs.

Any help is appreciated, thanks!

 

if the oil is just outside and surrounding the plug then it's just a valve cover gasket issue, but if it's at the end part of the plug ( where it meets the cylinder ) then it's a cylinder issue .. cud be a piston ring failure!

 

How much would it cost to do a piston job or valve cover gasket job, do you know?

 

Do a compression test of each cylinder

Telcoman

 

Most likely, and hopefully, it's a valve cover gasket/spark plug tube seal gasket problem. Your best bet is like one poster stated, do a compression AND leakdown test of the cylinder. This should really let you know if there is anything wrong internally.

 

Since you just changed the plugs i'm guessing a coil pack has gone bad. Is anything grounding out? Check for spark in cylinder 6.

 

Easy way is to switch the plugs and coils to the opposite bank and see if you still get misfire.

 

Finally got it fixed.

Cylinder #6 & #2 misfired were because #6 was not gapped right, #2 were not tightened correctly. That fixed the misfiring.

And there were a little oil where #6 was sitting due to a minor leak, I'm guessing it's from long ago and oil accumulated there at 105K miles, that's how small that little leak is.

The guy took out the valve cover gasket and he put a sealant coat over it. It might not ever leak again. Also, all the coil packs were still in good condition.

Problem solved Thank you for all of your input, they were greatly appreciated.