oil leaking into spark plugs

I just bought another xj yesterday and am pretty excited about it its a 98 with a 4.0 in it, the problem is it misfires, I pulled out the spark plugs and some of them had oil on them. any ideas what could cause this?

Bad oil rings, bad valve stem guides and/or seals.

Blow-by:
Check you air filter box for oil or since it's been wiped clean. Replace filter as needed. Clean all parts of oil.
Check TB for oil buildup. Clean as needed or do the seafoam trick.
Check you crankcase ventilation system for clogging. Clean as needed
Even with seafoam replace plugs.
A clogged vent system will sometimes suck oil into the airfilter. But most if the time it's just an old tired motor with excess blowby that clogs the tubs in the first place.
IF blowby was found in air filter system?
Excess blowby GENERALY shows up under high stress and/or high RPMs. If this XJ is going to be a DD with little stress? You could get lucky with little or no more problems.
If you intend to pull stumps with it. Repairs to control the blowby will be needed. Luck

Check the compression. This will show up bad rings and burnt valves. It is possible (although not likely) that an electrical problem like spark plugs, wires, or cap, could cause misfiring and let the spark plugs get oily.

Not to be an asshat but was the oil on the electrode of the plug or on the outside area?

Jeepm@n said:

Not to be an asshat but was the oil on the electrode of the plug or on the outside area?

Click to expand...

Not a bad question, the rest of us have all made an assumption.

the oil was on the electrode and the threaded part of the spark plug