Rough idle(burble) and dies at stops 89 yj 4.2 - Pirate4x4.Com : 4x4 and Off-Road Forum
 
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Old 12-08-2008, 06:35 PM   #1 (permalink)
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Rough idle(burble) and dies at stops 89 yj 4.2

Hi,

My wife's jeep has started this rough idle, I call a burble, it seems to idle fine, then every 50 or so revolutions, it will act like it misfires for 3 revolutions. It will stall at stop signs. I turned the idle screw out to stop the stall(most times). I've replaced fuel filter, air filter, plugs, wires, cap, rotor. The old plugs were white/tan but in pretty good shape. Took the top off the carb, and cleaned out all the passages I could see to the jets. I check the O2 sensor with my fluke DVM and it gives me 48mv at idle. I can run it up to 900mv by covering the carb intake with my hand. The engine didn't seem to care that I unplugged the O2 sensor, or the AIS. This makes me think it is running in closed loop mode. I don't think this year model has a check engine light. Anyone know how to code it out? Can you code it out? Carb cleaned the whole thing, cant find any vacuum leaks. Cant find my test gauge either..... Any help would be appreciated.

I'm trying to post a video I took of it running so you can see/hear my problem. I'll post up a link when I get it online.

Thanks
Dave

Last edited by dave E; 12-08-2008 at 06:36 PM.
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Old 12-08-2008, 07:39 PM   #2 (permalink)
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Ditch the stock carb for a Weber or a Motorcraft. I don't know anyone with a carbed YJ that doesn't have this problem. the new carb allows you to get rid of the crazy air-pulse system, too.
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Old 12-08-2008, 07:46 PM   #3 (permalink)
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Gotta stay California smog legal. (yeah sucks I know)
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Old 12-08-2008, 08:09 PM   #4 (permalink)
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mine still runs like shit with a weber, but it looks cleaner with out all them vaccum lines
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Old 12-08-2008, 11:33 PM   #5 (permalink)
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have you cleaned out the idle pick-up tubes in the venturi cluster in the carb? i have done this many times when it started acting up.............works wonders and easy 10 minute job. here is a guys pretty good description of how to do it ( although i never drilled out the tubes as he describes). just pull the two pick-up tubes out and BLOW them out with compressor and put back together.

http://www.jeepforum.com/forum/showthread.php?t=6502

Last edited by rockrknockr; 12-08-2008 at 11:34 PM.
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Old 12-09-2008, 12:17 AM   #6 (permalink)
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Get a main body from a late 70's dodge 318, along with the metering rods and jets, swap the top and bottom sections and get rid of that stupid computer controller....most people will never recognize that its missing. I did it to mine and it would idle @650 perfectly with an auto. Or do the nutter bypass. Tim
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Old 12-09-2008, 09:14 AM   #7 (permalink)
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It just started all this about a week ago. I'm hopeing to put it back to good running condition at least for a little while. Is there a chance that it could be something more serious like a slipped timing chain? I disassembled and cleaned the carb as best I could with carb cleaner since my compressor is non functional ATM.
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Old 12-09-2008, 12:23 PM   #8 (permalink)
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Check with your local Referee, and see if you can legally swap out the intake system for a renix MPFI from a Cherokee or Commanche of same year or newer. Even going to a induction system from a 91-95 OBD1 YJ should bolt right in with limited problems. Thats if you have the time or cash. What about any after market Carburator that is CARB compliant?

Edit: im a dumbass
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Old 12-09-2008, 05:01 PM   #9 (permalink)
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Quote:
Originally Posted by rockrknockr View Post
have you cleaned out the idle pick-up tubes in the venturi cluster in the carb? i have done this many times when it started acting up.............works wonders and easy 10 minute job. here is a guys pretty good description of how to do it ( although i never drilled out the tubes as he describes). just pull the two pick-up tubes out and BLOW them out with compressor and put back together.

http://www.jeepforum.com/forum/showthread.php?t=6502
a cloged venturi has been my experience as well. A .032 bit works fine I dont know about the .040 size . If its a constant clogging problem, clean tank and change filter. If you adjust your mixture screws do it with the computer unpluged from the carb, otherwise it will compensate.
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Old 12-09-2008, 06:34 PM   #10 (permalink)
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Originally Posted by dave E View Post
It just started all this about a week ago. I'm hopeing to put it back to good running condition at least for a little while. Is there a chance that it could be something more serious like a slipped timing chain? I disassembled and cleaned the carb as best I could with carb cleaner since my compressor is non functional ATM.

probably not good enough..........if you didn't pull the idle tubes and BLOW them out then there is still minute particals plugging them...........happens all the time with this carb. trust me, simple fix and will make you SMILE
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Old 12-09-2008, 07:10 PM   #11 (permalink)
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I took a peice of wire and cleaned the pickups out pretty good I think. I didnt really see anything come out. Time and cash are hard to come by right now.

Is there any chance this could be a slipped timing chain? My wife heard a bang while she was pulling away from a stop light a while back and shortly after that this started. Not sure of exact how long after though.

She is planning on driving this to canada (1800 miles round trip) and will have to rent a car $$$ if I cant get this fixed.


Dave
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Old 12-11-2008, 10:42 PM   #12 (permalink)
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ok well new info on my part. I took the idle air control stepping motor off and extended the needles all the way out. I had not seen them move since I started this whole trouble shooting effort, and I wanted to see if they were actually moving. After I reassembled the carb and started it, they did not move, but the engine seems to have regained the 400 rpm it had lost when I started. The O2 sensor mV bounces all around now. Any one know how to test the idle air motor? Im not sure if its bad or the computer isnt commanding it open. Now I am worried that I have a burned valve from it running lean so long. Compression test tomorrow.
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Old 12-12-2008, 03:50 PM   #13 (permalink)
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ok well new info on my part. I took the idle air control stepping motor off and extended the needles all the way out. I had not seen them move since I started this whole trouble shooting effort, and I wanted to see if they were actually moving. After I reassembled the carb and started it, they did not move, but the engine seems to have regained the 400 rpm it had lost when I started. The O2 sensor mV bounces all around now. Any one know how to test the idle air motor? Im not sure if its bad or the computer isnt commanding it open. Now I am worried that I have a burned valve from it running lean so long. Compression test tomorrow.

now that you mention this.............i remember that i had a similar prob and i disconnected the stepper motor while the needles were all the way out and then just left it dis-co'd and it ran great?????

GET FUEL INJECTION

Last edited by rockrknockr; 12-12-2008 at 03:51 PM.
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Old 12-12-2008, 05:28 PM   #14 (permalink)
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If you leave the needle extended you should be fine. make sure your wires are pluged in when you reconnect to stepper motor. mine had a tendancey to push out the rear. I have a couple extras in the garage if your around sacramento.(oh yeah ....yea fuel injection, no more problems..so far.)
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Old 12-12-2008, 06:58 PM   #15 (permalink)
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GET FUEL INJECTION
Yeah I want to put a chevy multi port fuel injection system in it. The best way I can see doing that is to mount it to a chevy 4.2 straight 6 engine.

Sadly there is one major problem with going to fuel injection of any type. I'm one broke mofo.


tgariano, I would love to borrow a stepper motor(I'm 30 min west of sac). I ran it with it out today, and could feel it trying to move, but it didnt seem to be able to, although with the engine off I can move it easily.

Thanks
Dave
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Old 12-13-2008, 08:42 PM   #16 (permalink)
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Since it was mentioned to me, here is a link to a site about the GM 4.2 straight 6.
http://www.canadiandriver.com/articles/jk/at_010424.htm

Tgariano let me try his IAC motors and none of them worked for me either. I'm thinking computer at this point. $129 at napa, kragen didnt list one....sigh.

btw since I mentioned it 110 to 120 psi on all cylinders except #5. 90psi on 5. Not happy about that, but will live with it for now.

Any one have a spare working computer out of an 89 wrangler?

Dave
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Old 12-20-2008, 05:43 AM   #17 (permalink)
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On my Dads 89 YJ I was having the same trouble, that carburator is junk, however what I did to it was the stepper motor, nutter bypass and put in a new ignition control box and the thing runs great. Every now and then it will die but that usally when hitting a big bump and/or going up a hill but it's rare.
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