Just bought a V6 4.0 '97 Ford Ranger with 50,000 miles. Engine ran fine. No noises. Exhaust appeared normal.

After less than two weeks began misfiring. Pulled plugs and found that the #5 cylinder plug was caked with oil causing it to misfire. Checked compression on all cylinders. Compression was similar on all cylinders including # 5 around 160. In the two weeks it used at least a quart of oil, but again showed no signs of burning it.

Found this post on the internet:
"Check your spark plugs for oil fouling in the center cylinders. ( 2 and 5)
Your intakes may need to be retorqued as the are often so loose the vacuum
will draw oil from the lifter valley, particularly in the central cylinders.
They burn so slowly that the exhaust is not even blue, but often the engine
pings due to carbon build up."

All of the intake bolts were loose, the worst was over the #5 cylinder. Re-torqued bolts. I've run it for probably 50, no more than 100 miles and it's used at least half a quart of oil and the #5 plug is again building up oil and carbon residue.

Any ideas on what might be causing this?

 

valve guide seals or pistion oil rings. bout only other things that can cause this issue

 

Im goin with valve guide seals as well. If you did a compression test and all tested normal thats about your only option if you already checked your valves. If your rings were shot they should show on the compression test. With a truck that old and low miles your valve guide seal are prob dried out from sitting so much and not being ran. If you ran it 50 to 100mi and used a half a quart of oil i would think it would show when you drive it.

 

If you are leaking oil and you're comp tests were spot on then it can still be the rings, the oil is just sealing them. the valve seats would blow the compression test either way.

I am pulling the heads off mine right now to check the same thing, my guide seals that is. Going to regrind the seats out regardless, that is if they're not just cheap *** press-ins.