2000 XJ 4.0L found a new mudhole today. when we were done my jeep was sitting there idling, then it just started to run rough. took it in to check the computer and it was showing cylinder 2 and 3 misfire and O2 censor failure. at one point my exhaust did go under water for about 2 minutes, but i kept it running that whole time. i can get a new O2 censore, but how do I fix the misfire? i know for a fact the motor was never even close to being under. could the o2 censor cause the misfire?

 

or you may have a split or cracked spark plug wire and when you were muddin you got it wet and therefore it misfired butthe heat of the engine dried it out and you never even noticed happened to my wrangler when i first got it i found the biggest mud hole and went for it died my 3rd time through took let it sit and then it fired right up went to the car wash and pressure washed my jeep left it running ( just after i got it started up after the mud hole) and it once again died let it sit started up and took it to my mechanic he checked the wires and they were original from 95 as soon as he sprayed a little water on them it died took them off put neww ones on and not a problem since. old ones had visible cracks though in the insides of the bends

 

replace your plugs wire cap and rotor before the o2 and see if that fixes it also pull your o2s and take some fine gritt sand paper and ruff them up and see if that fixes your problem o2 sensors are $$$$$ i had to replace both of mine the other day

 

O2 sensors have to breathe... If the vents on the sensor are blocked, the O2 can't work.

They work by creating a low-voltage AC current when the oxygen content of the exhaust differs from the oxygen content of the atmosphere (thanks NASA).

Pull the sensor(s) and clean with brake spray and compressed air. Pay attention to the slits or pinholes in the sleeve on the outside of the sensor, not just the ones in the tip.

 

i pulled off the o2 sensor behind the cat. it looked really black but other than that it looked fine. im gonna try to clean it up a bit. maybe pull off the one in front of the cat and see what it looks like.

 

just cleaned off the front o2 sensor. about the wires and distributor, mines a 2000 so it has a cap over plug with no distributor, ill probably still replace the plugs.

 

VICTORY!

cleaned off both O2 sensors. after that i could tell the jeep was running alot better. I went ahead and replaced the spark plugs as well, since they are the same ones that were in there when i got it. the things running like a champ. thanks for the input guys!