Pulled plugs, 1 is oil fouled

olyfiveoh

New Member
Dec 27, 2004
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I have a 90 GT that is for the most part stock except for an o/r xpipe, and mac induction tube. I recently saw my fuel economy drop way off and did a tune up.....oil, plugs, air filter. One of my plugs was a bit fouled and so i checked the new one after 200 miles of driving. the new plug was extremely oil fouled and looked as though it was not even firing. This obviously leads me to believe that there is an oil leak into that cylinder, however, my car is not smoking at all and does not appear to be losing much oil either (it always burned a little). when driving, the car seems to be firing all 8 cylinders and the power seems normal. My MPG went from around 17-19 to 12-14. Any ideas on what the cause could be?
 
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If after you change the pcv valve and it still fouls out, (I think it will) pull off the drivers side valve cover and see if the oil return hole is partially pluged. You see the engine slopes toward the back and if oil is slow at draining down the hole in the end of the head it will drain down the first valve guide it comes too.#8
So make sure the oil drain hole is not plugged, use coat hanger etc. to make sure.
 
So i know this is an old post but I had my car put away for a while. i changed the PCV and the bad plug and then put it away until the summer. i just drove it up from storage which is about a three hour drive and after checking the plug, it is fouled again, just as Whitegt predicted. Are there oil return holes on each head, or just the drivers side? Will it be pretty obvious where it is when i pull the valve cover? pictures anyone?
 
So i know this is an old post but I had my car put away for a while. i changed the PCV and the bad plug and then put it away until the summer. i just drove it up from storage which is about a three hour drive and after checking the plug, it is fouled again, just as Whitegt predicted. Are there oil return holes on each head, or just the drivers side? Will it be pretty obvious where it is when i pull the valve cover? pictures anyone?

Little holes on the front and back ends of both heads.
 
Not to be the bearer of bad news, but to me this sounds like a valve seal. Basically when the car sits, the oil leaks down into the cylinder. Fouling the plug. When the car is running there is not a substantial amount of oil dripping down, so you will not see it burning.

Another possibility that I am very familiar with is a lower intake gasket leak. If you have a lower gasket leak the cylinder will pull oil from the lifter valley into the cylinder and foul the plug. However you will be able to identify that by opening the oil filler cap and see if there is any change in vacuum.