Help! Idle/driving problems on MJ

My 87 manche has a tendency to feel almost like some cylinders arent running sometimes. When your sitting at a stop, the exhaust sound coming out with the rear slider open...sounds like a poorly tuned carb'ed motor and when you shift it into drive, theres a vibration feeling coming up and it feels like the motor does not have much power....When you let your foot off and keep the speed, just say 45mph, the vibration is gone and the motor feels like its running fine....It used to be really bad but then i replaced the alternator and that helped fix the real poor idle part.

Today, i did the rear main seal and cleaned some crud off the bearing caps ect....bolted up the pan, filled it back up, and drove it...At this point the jeep hadnt run in nearly a day and a half....I cranked her up and drove, WOW!!! No more vibration and the motor felt like it was running as smooth as anything, i came to a stop about 5 minutes after driving it and then drove it to a friends house and shut it off for a another couple minutes...Start it back up and same damn vibration and rough idle when stopped and driving...Grrr...


oh and its running extremely rich and is now smoking...not smoking terribly, but smells and smokes a little bit...i think like rich....alot of vacuum lines are running everywhere....

TPS?

maybe?

I dont understand why after doing the rear main and cranking it back up cold, it ran so smooth and had so much more power...?

any help woudl be great. PS, when i say it vibrates, it feels like a motor mount might be shot, my tool box rattles in the back; thats how bad the idle and driving is!



-alex

Leave it running rough for a minute or so and then switch off the engine, pull the spark plugs and compare them. Any of them look different?

You could also try removing the plug leads (with a well insulated pair of pliers!) one at a time, and see if one makes little or no difference. You can also do the same thing with the injector leads, assuming you are multi point fuel injection.

Ok, i havent tried pulling the wires yet off the plugs but i will...i was leavin the bar last night and i started it up and it ran JUST FINE, i came to the stop light about 4 miles down the road still in drive to make a U turn...Sure enough i make the turn and it is doing the same damn thing...Im beginning to think that maybe a wire may not fully be on a plug or perhaps my coil is shot?

what do you think.

How old is the oxygen sensor? That's what controls the air-fuel mix. If it's more than 75,000 miles (or maybe 80,000) it is due for replacement.

It's possible that when you dropped the pan to do the seal you disconnected or jiggled the wires, remporarily improving the connection for a marginal sensor. Also, remember that for the first few minutes/miles, the Renix system doesn't use sensors, it operates in open loop mode according to a pre-programmed fuel map -- so until the temp gets up close to normal operating range, the engine isn't responding to the O2 sensor at all. On cold days, I can literally feel when mine switches over from open-loop to closed-loop.

Ok, im gonna check first to make sure all wires are off the block so they might not be arcing before they hit the plugs....Secondly i'll check out the sensors....How bout 190,000 miles on the motor...Not sure if they are the same sensors that came with it...or not....

How many o2 sensors does a 87 4.0 fuel injected motor have? this is in the commanche. im thinking about replacing them...i checked the plug wires and they all seemed to be on good and i made sure they werent arcing on anything...

-alex