96 xj multiple misfire issue

[thinmints]

96 xj with 275000. 4.0 Over the last several months i have developed a problem of having multiple mis fires in the #6 cylinder, it started out when i was at a light the engine wouldn't idle smooth and the occasional misfire would occur but after time the mis fires would increase to the point of my check engine light would come on, the code reader said multiple mis fire in the # 6 cylinder. i replaced the spark plug and it fixed the problem but after a month or so the same issue happened again and again the check engine light came on and its the # 6 cylinder i replaced the plug again, and all was well but i have noticed that its starting to mis fire again i cant figure out why the #6 cylinder keeps developing this problem HELP!!!!


PS i have replaced the cap and rotor, plug wires are only a year old

[72mino]

How does the plug look? Is it oily? If so you could have oil leaking past a piston ring.

Dustin

[fredjacksonsan]

How many miles do you get out of a new plug before it starts missing?

Agree with 72mino on the oiled up plug.

Multiple misfire can also be caused by a bad Crankshaft Position Sensor; not bad enough to misfire with a new plug, but as the old one ages the cumulative electronic degradation gets to be enough to cause a misfire. Just guessing here.

[thinmints]

i get about 2000 miles on it before i start to get any problems, when i pull the plug, to me it looks ok and is not oily, at first i thought the gap might have been off so i was very careful to gap it correctly this last time so we will see what happens, i'm going to replace all my plugs in the next few weeks and i may just replace the wires as well