My 3.0 ranger is running prety crappy, when it idles it sounds like a constant miss. I just replaced the plugs and 5 out of 6 looked great, the #6 plug was coated in oil and fouled out. After 50 miles i pulled and replaced the plug, as it was already fouled out again. Any comments or suggestions? still getting 30 mpg running like crap.

 

You have to try and figure out what's going wrong in that cylinder. Are you sure it is oil that is fouling the plug? If it is oil you'd be seemingly be noticing some blue smoke out the tailpipe, abnormal oil consumption, even the smell of it. Oil could get into the cylinder through worn piston rings or valve seals, I would think.

When you pulled the plug again, was it wet with fuel (leaking fuel inelector) or have a greenish tint to it (head/head gasket issue)?

On any case it sounds like a compression check is in order.

 

Do you know when the plug wires were changed? A bad plug wire will make a plug foul out also.....

 

When i was replacing the plugs all were burning well except the #6 (drivers side rear). It had alot of wet crud, looked like carbon deposits and the gap was bridged. After replacing it and driving 120 miles it was fouled again.

Its definitly oil I think, plug has heavy carbon deposits after 50 miles,but is dry. I put a defouler on it today and its still geting carbon buildup but not as bad. Theres fire going through the plug wire, ill swap it with another wire to try that though. It uses/loses roughly 1 quart per 60 miles. I know it has a rear main leak so that explains part of the oil loss. Im going to try a hotter plug tomarow to bandaid it as i have to have it to get to work. Compresion check coming this weekend, along with a new valve cover gasket, so ill have a chance to see if the oil return is cloged causing it to be sucked down a valve. I hope its just valve seals, i have replacements. If it is the oil control ring would it be feasable to pull the #6 piston with the engine still in the truck and just replace the oil control rings? I can do a normal head gasket job in a day, so i figure a weekend to do headgasket and rings on the one piston.

 

You didn't mention the year or mileage.

If a compression check and other tests confirm the engine needs that kind of work, I personally would scan the local yards for another 3.0L (they are plentiful in most areas) and seriously consider going the swap route.

 

The truck is a 93, the engine was a used replacement put in about a year ago, not shure of its year.