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Fed up and pissed off!

94XJ2door5speed

94XJ2door5speed

NAXJA Forum User
Location
Norwich, CT
Ok so put a new O2 sensor in today, did like everything else, ran awesome for 20 minutes then back to skiping. Its still at around 2000 rpm. So now with the cash ive spent on sensors alone i could have put my 350/350 into it and twisted the subframe in half. So im left with 2 options: fuel delivery and timing. I'm leaning towards fuel delivery but my nice guage from advanced says ive got plenty of fuel pressure so what is the deal. It only happens under load and im getting sick of it. I would put a brink on the gas pedal and watch it self destruct but i know it would just sit there until it ran out of gas(been there done that) Anyone got a clue as to why one day it was fine and the next this skipping problem? The crank sensor died one day unexpectedly and ever since it doesnt run right(and ive tried 2 other crank sensors so its not that)
 
Give us some details about your junk first. Then do a search for TPS. Check engine light on? Most of the electronic sensors are controlled buy your PCM and therefore a code scan can help you determine what's going on. But, that all differs year to year so reread my first sentence...
 
Search engine does not work for 3 letter words, no less than 4 is required, so seach for throttle position sensor and read up on testing them and what the symptoms of a bad one are.

If it's a 94 check the error codes.
 
Well lets see no CEL. no codes found. replaced ready for this, cap, rotor, plugs, wires, TPS, crankPS, camPS, O2 sensor, fuel filter, ignition coil, tested my computer in another jeep ran fine. Fuel pump is good. The jeep ran great when i bought it ok. Got home turned it off. Woke up the next morning it wouldnt start no spark. So i did full tune up theres the list of stuff i replaced. Ever since then it has skipped, it didn't before only after that stuff was replaced. Only thought is that there was crud in the tank and it plugged the new filter almost instantly. So now i pay closer attention and it is really only when it is under a load so i'm thinking fuel delivery, have ran 6 different types of fuel system cleaner since i bought it cause it sat for 11 month bofore i came along and bought it. I also replaced front axle u-joints tranns mount, motor mounts, sway bar bushings, rear output seal on t-case and front calipers and rotors. Those won't affect the motor though. Can't find a vacuum leak either, I do have a cracked manifold but don't know if that will affect it. Thought the jeep was a steal at $800 but not so sure now. I'm gonna try another fuel filter when its not 10 degrees out even thought its only got 1,500 miles on it.
 
Just a thought, try pulling your fuel rail off and see if there is any rust in it, it is possible that since it sat so long you got condensation in your fuel line, and have a paritally plugged injector with rust scale.

be sure to spend another 5 bucks to replace the injector o-rings while you have them out.
 
cool a new idea, as soon as it gets a little warmer i will try it ill try anyhting at this point.
 
good idea goodburbon, also you might check your grounds to the engine and firewall, bad grounds do some weird stuff. BTW I don't remember from your other post's, but your not running bosch platinums are you?
 
nope changed them last weekend to stockers very very happy with that. I don't reget what ive done all of it has made the jeep run much much better i just want the skip gone!
 
94XJ2door5speed said:
Well lets see no CEL. no codes found. replaced ready for this, cap, rotor, plugs, wires, TPS, crankPS, camPS, O2 sensor, fuel filter, ignition coil, tested my computer in another jeep ran fine. Fuel pump is good. The jeep ran great when i bought it ok. Got home turned it off. Woke up the next morning it wouldnt start no spark. So i did full tune up theres the list of stuff i replaced. Ever since then it has skipped, it didn't before only after that stuff was replaced. Only thought is that there was crud in the tank and it plugged the new filter almost instantly. So now i pay closer attention and it is really only when it is under a load so i'm thinking fuel delivery, have ran 6 different types of fuel system cleaner since i bought it cause it sat for 11 month bofore i came along and bought it. I also replaced front axle u-joints tranns mount, motor mounts, sway bar bushings, rear output seal on t-case and front calipers and rotors. Those won't affect the motor though. Can't find a vacuum leak either, I do have a cracked manifold but don't know if that will affect it. Thought the jeep was a steal at $800 but not so sure now. I'm gonna try another fuel filter when its not 10 degrees out even thought its only got 1,500 miles on it.
Click to expand...

Now we are getting somewhere!!! A cracked exhaust manifold will draw fresh air, thus fresh O2 and fool the O2 sensor. Disconect the O2 sensor, if the skip goes away, its the cracked exhaust manifold in combination with a good working O2 sensor that is causing the problem. :D
 
Ecomike said:
Now we are getting somewhere!!! A cracked exhaust manifold will draw fresh air, thus fresh O2 and fool the O2 sensor. Disconect the O2 sensor, if the skip goes away, its the cracked exhaust manifold in combination with a good working O2 sensor that is causing the problem. :D
Click to expand...

While you're mucking about down there, grab a 9/16" socket and check the stud nuts for the flange on the downpipe - a leak in that area need not be cracked tubes...

Oh - and check the screws for the manifold as well. They sometimes work loose (because aluminum expands twice as fast as iron, check screws where they have to clamp both iron and aluminum...)
 
Last edited:
Ecomike said:
Now we are getting somewhere!!! A cracked exhaust manifold will draw fresh air, thus fresh O2 and fool the O2 sensor. Disconect the O2 sensor, if the skip goes away, its the cracked exhaust manifold in combination with a good working O2 sensor that is causing the problem. :D
Click to expand...
Good catch. I breezed right over that in his post. Had to go back and read it again to see it. You are probably right on this one if he actually has a cracked header. Helped a buddy pull his off to weld it and couldn't find a crack anywhere. Pulled everything off. Replaced gasket and VOILA no more cracked header. Sounded like a different Jeep.
 
I recently worked on a friends grand with the 4.0 and I tested fuel pressure to be fine. I was thinking maybe fuel filter or O2 sensors, but fuel pressure was fine. Told her to have them hook it up and test it. They tested it to be fuel pressure inadequacy.

Fuel filter was the problem.
 
dirt machine said:
I recently worked on a friends grand with the 4.0 and I tested fuel pressure to be fine. I was thinking maybe fuel filter or O2 sensors, but fuel pressure was fine. Told her to have them hook it up and test it. They tested it to be fuel pressure inadequacy.

Fuel filter was the problem.
Click to expand...

From his comments, I gathered he had a very specific, engine rpm, 2000 rpm, skip. A fuel pressure or flow rate problem would cause more widespread rpm and engine load problems, not just a skip only at 2,000 rpm. That makes it sound like a resonate, tuned suction of air through a cracked exhaust manifold, or bad manifold gasket, or loose manifold bolts, that is suddenly upsetting the O2 sensor with a unexpected excess oxygen supply. It's an easy test to determine, just disconnect the O2 sensor connection, and see if the 2000 rpm skip stops. If it stops, fix the leak and reconnect the O2 sensor.
 
Have the same problem with my 88 MJ 4.0. tried all the things that you did with no improvement. This week-end my son-in-law happened to mention that when he had a load of firewood on the jeep, it did not skip/stutter at 2000 rpm. That got me to thinking....could the load cause a some sensor to come closer to whatever it is supposed to monitor and get a better signal? I had ruled out CPS because the truck starts and runs fine, but now I am beginning to wonder.......
 
Guess what i put a trailor on it the other day well like a month ago and there was no skip with the sever load, so i don't know its really bad today i was in the city where you have to stop everyblock or so, so you never leave second or go over 2 grand really.(which seems to be the trouble spot 2nd and 4th at 2000rpm or just below) It was horrible the guy with me was like where did you learn to drive stick?
 
Ecomike said:
From his comments, I gathered he had a very specific, engine rpm, 2000 rpm, skip. A fuel pressure or flow rate problem would cause more widespread rpm and engine load problems, not just a skip only at 2,000 rpm. That makes it sound like a resonate, tuned suction of air through a cracked exhaust manifold, or bad manifold gasket, or loose manifold bolts, that is suddenly upsetting the O2 sensor with a unexpected excess oxygen supply. It's an easy test to determine, just disconnect the O2 sensor connection, and see if the 2000 rpm skip stops. If it stops, fix the leak and reconnect the O2 sensor.
Click to expand...
Thank you very much for a different idea, thanks to everyone that suggested the leak but, when i bought it it ran awesome especially for it sitting for 11 months and stale fuel. Why would the leak that had been there since the begining start causing problems suddenly, other than the motor mounts were shot so me torquing on the exhaust could have caused it to get worse as i drove with bad mounts. Huh. well i will see but before i changed the Os sensor for the new one i road around for a while and it didn't really skip until the CEL came on then it got worse( but it never went away either) plugged it back in and viola it was gone for about 20 min's then this headache again. What ever i play with elecrtically, whether its simple like unhooking the coil, or CPS, or cam sensor, and then just plugging them back in, the skip disappears for like i said 20 minutes then its back???
 
Nope, never thought of that, well actually it was cold when i unplugged it but it was hott when i plugged it back in. and it skipped both ways. Thats why i replaced it that and it had 200,000 miles on the stocker.
 
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