Nissan Repair: 1995 Nissan Quest Van miss-fires during Acceleration, nissan quest, exhast

Question
I have a 1995 Nissan Quest Van that backfires during acceleration. I have changed the plugs, distribution cap / rotor, and wires inclusive. However, the problem is still evedent. I have also checked the air filter housing for leakes. But no leakes was evedent. The van is slugish at best. Part of my muffler was blown off during one of the backfiring events.  I was informed that a bad Cat-converter or a sticking exhast valve might be the culprit. Please advice. Thanks.  

Answer
Onaz,

It is probably the distributor.  Under the cap and rotor is a metal cover.  Under this cover is the optical pickup that lets the computer know when to fire the plugs.  Well, the pickup gets oil on it when the internal oil seal goes.  Install a rebuilt distributor and you should correct the problem.