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93 4.0 with terrible stutter


 
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cazman
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Joined: 29 Jul 2008

PostPosted: Tue Jul 29, 2008 5:24 am    Post subject: 93 4.0 with terrible stutter Reply with quote

Please lend a hand...

I've got a 93 JGC with 127K miles. It began occasionally stuttering about 6 months ago. It would come and go so I didn't think too much of it. No however it has vome to stay and it's violent. It idles poorly and when driving it sounds like it's running on 4-5 cylinders. It's worse when accelerating. But it's BAD! It was suggested that the crank position sensor was bad so I replaced that. No improvement. I've replaced the plugs, cap, rotor, wires, crank sensor, fuel filter and O2 sensor. Still no better. It's worse under load and every time the AC compressor would kick in while idling it would get worse. So I pulled the fuse for the AC. It idles 'better' but still misses and it that did nothing for the acceleration or drivability. The stutter is most horrible between 1500 and 2000 RPMs then again between 2500 and 3000 rpms.

My next thought was to replace the coil and the ignition control module in the distributor.

Any thoughts or suggestions? I'm not getting a check engine light and have not had it plugged in to a code reader.

Thanks for the help.
Caz
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IBTJn
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Joined: 31 Dec 2004
Location: Just Outside of Portland, OR

PostPosted: Tue Jul 29, 2008 5:57 am    Post subject: Reply with quote

Sounds like a vacuum leak to me. That's usually the place I start when all the other obvious things have been checked.
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cazman
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Joined: 29 Jul 2008

PostPosted: Tue Jul 29, 2008 6:29 am    Post subject: Reply with quote

Oh joy...

57 vacuum lines and not a clue how to even start the process of elimination.

But thanks IBTJn. Any and all advice is appreciated. Is there a "good" way to tell right off if the vacuum system is leaking someplace? A single hose perhaps that can be drawn down or pumped up and timed to see if the pressure + or - bleeds off?

Caz
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IBTJn
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Joined: 31 Dec 2004
Location: Just Outside of Portland, OR

PostPosted: Tue Jul 29, 2008 1:07 pm    Post subject: Reply with quote

I know on the older XJ/MJ"s the stealership has a replacement vacuum line kit you can buy. In spite of me not liking to buy from them, I got one for the old MJ I had (it REALLY needed it!). Believe it or not, it was probably one of the best services I did on that old rig! I understand well about what a PITA dealing with vacuum lines is...but if they haven't been checked/replaced I would certainly do that. If only a little at a time and mark them. The kit I got included some other stuff that frankly, I wouldn't have thought to replace (or would go bad) but with vacuum lines, all bets are off. Namely some of the tee connectors and stuff that are vinyl or polypro material (plastics) that crack over time. It was such an easy thing to do I went ahead and got the kit for the wife's XJ as well at about 130k miles. She now has 180+K on it, and it still runs like a champ!

If you aren't into that, take one line at a time and inspect/replace as needed. yes it takes a long time...but believe me, one bad vacuum line can not only affect fuel mileage, but make the rig run like crap.

Just some thoughts. Wink
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swamp boy
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Joined: 01 Jan 2004
Location: New Orleans LA.

PostPosted: Wed Jul 30, 2008 6:46 pm    Post subject: Reply with quote

the easiest way to check where your vacuum leak is , is to get some carb cleaner and spray it on each line while the jeep is running .. If they idle changes while you are spraying ... Thats your line...

Dont go crazy spraying it everywhere.. A little goes a long way..

It wont take much to affect idle when you hit a cracked or broken line..

Changing them all will definaltly be your best but.. Just offering info..

Good luck..
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XIONG1
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Joined: 29 Jul 2008

PostPosted: Thu Jul 31, 2008 4:57 am    Post subject: Reply with quote

just you say!
good luck.
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cazman
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Joined: 29 Jul 2008

PostPosted: Thu Jul 31, 2008 6:01 am    Post subject: Reply with quote

Thanks... Still working on it. I'll try the carb cleaner on the vacuum lines. But I'm having a really hard time accepting that what I'm experiencing is from a vacuum leak or a fuel delivery problem. The miss/sputter is VIOLENT and feels more like repetetive mis-firing in one or more cylinders. My gut is telling me it's got something to do with the electrical/ignition/timing systems. I'd say that the timing chain skipped a tooth and is way off but then it should be a constant thing and not be worse at some times than others. (Meaning mis-fire, mis-fire, mis-fire, quiet, quiet, quiet, quiet, mis-fire, misfire, etc.) Also, since it originally came on a little here, a little there, and then no problems at all for weeks, then a little here, a little there, until finally it became constant, I'm thinking that if it were the timing chain/gears it would have been like throwing a switch. Click - here's a problem. Also, unlike a timing belt, chains and sprockets should have more than a 125K mile lifespan.

What about the electronic module in the distributor?
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Orangeamc13
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Joined: 20 Feb 2006
Location: East Springfield, Massachusetts - U.S.A.

PostPosted: Thu Jul 31, 2008 8:46 am    Post subject: Reply with quote

Try cleaning the IAC. It never hurts to have it clean!
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