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Cylinder 8 Misfire

Old 03-15-2019, 06:07 PM
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G-Turo
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Default Cylinder 8 Misfire

Okay so I have a 2011 GT 6 speed with 93xxx miles and for the past few months i have had a p0308 code and my spark plug on cylinder 8 keeps getting fouled. So i have replaced all coil packs and spark plugs and cylinder 8 keeps getting fouled in just a few days. So I had a buddy drive behind me for a while and it appears that the only time that there is blue smoke from the exhaust is when i start it in the morning there is a quick poof of blue smoke or when I rev it with no load on it (in neutral or clutch depressed). If i do a hard acceleration, the only time that i see smoke from my exhaust is when i push in the clutch to grab the next gear and then it goes away when i get back on the throttle. What could this be? Wouldnt bad piston rings smoke constantly and not just when im in neutral??
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Old 03-15-2019, 07:42 PM
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JimC
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So the forum is causing your issues with your car?
Forum Issues and Feedback Discuss any issues you are having with using Mustang Forums here.
That's what this section is about. For questions related to your car you need to post in the correct section. There is a section just for the S197 (2005-14 model years) that you need to use.
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Old 03-16-2019, 08:13 AM
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99GTvert
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Moving to tech..
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Old 03-22-2019, 01:33 PM
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Derf00
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P0308 has nothing to do with the coils. That would be P0358. If you replaced your coils with cheapo's, before you do anything else, put the stock ones back on before you end up with other problems from the cheapo's.

Anyways, P0308 is misfire related to either fuel or valvetrain. In this case, since you have blue smoke (oil burning) you either have singed piston rings in #8 or a failing valve stem seal. You can easily rule out the piston rings with a compression check. If that is fine then you're looking at valve stem seal.s I don't know if they can be replaced with the head on the car (just removing the cam) or if you have to pull the head. Either way, it's best to replace all the valve stem seals on that head if one is bad.
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Old Yesterday, 12:00 PM
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Dino Dino Bambino
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The problem is almost certainly a bad valve stem oil seal on at least one of the valves of the no.8 cylinder, causing oil to leak from the crankcase past the valve stem into the combustion chamber. That would explain the blue smoke on start up and with no engine load, and explain the plug fouling.
However some early Coyote engines had an issue with the no.8 cylinder running hotter than the rest. With insufficient cooling of the exhaust valves, the valve guides would wear prematurely causing the same problem that you've described as well as a light ticking sound. Therefore you'll need to check if there's any excessive movement of the valve stems inside the valve guides on the no.8 cylinder, particularly on the exhaust side.
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Old Yesterday, 01:36 PM
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Derf00
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Originally Posted by Dino Dino Bambino View Post
The problem is almost certainly a bad valve stem oil seal on at least one of the valves of the no.8 cylinder, causing oil to leak from the crankcase past the valve stem into the combustion chamber. That would explain the blue smoke on start up and with no engine load, and explain the plug fouling.
However some early Coyote engines had an issue with the no.8 cylinder running hotter than the rest . With insufficient cooling of the exhaust valves, the valve guides would wear prematurely causing the same problem that you've described as well as a light ticking sound. Therefore you'll need to check if there's any excessive movement of the valve stems inside the valve guides on the no.8 cylinder, particularly on the exhaust side.
That's actually a good point. I had totally forgotten about that. Funny, That's what caused Ford to release that stupid TSB about engine tunes and how that could void your engine warranty. I don't recall all of the details but for those that did fail and Ford covered (stock motors), it was a burnt/cracked piston due to the insufficient cooling... Hope it's not that!
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