Nissan Repair: 1995 nissan quest rough running, crankcase pressure, distributor shaft

Question
My 1995 Quest starts fine but after running for a while the engine starts to miss, backfire and generally run rough. It has about 159k miles on it and I tried replacing the dist rotor and cap,spark plugs, wires,and fuel filter. Still does the same thing. Any suggestions.

Answer
George,

It is probably the distributor itself.  As the engine wears so do the rings and that causes blowby.  The crankcase pressure along with a distributor shaft seal that does not seal well allows oil to wick it's way up the distributor shaft.  Your Nissan uses an optical pickup and shutter wheel much like the mouse on your computer.  Oil on the shutter wheel and the optics leads to misfire and such.  If you take the distributor a part you will find oil on the shutter wheel and optics.  If this is the case replace the distributor with a rebuilt unit and you should correct the problem.