Jeep 1990 YJ nuttered,motorcraft no vacuum leaks won't idle runs crazy rich. - Jeep Wrangler Forum

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Old 05-04-2013, 05:07 PM   #1
Join Date: May 2010
Location: Boise ID
Posts: 10
Jeep 1990 YJ nuttered,motorcraft no vacuum leaks won't idle runs crazy rich.

Alright guys, just purchased a 1990 jeep YJ 4.2 with the 5 speed. It ran great in all gears but wouldn't hold an idle and died when I put the clutch in at stops. I tried the nutter..nothing. So I installed the motorcraft 2150 from the eBay guy with no change. Triple checked the vacuum lines and timing. Had a loose intake bolt fixed that. New plugs,wires,coil,cap still runs super rich and dies. The starter grinds sometimes when trying to fire and it sat for about a year. It does have exhaust leak at the donut i think as well. Any ideas?

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Old 05-04-2013, 06:46 PM   #2
Join Date: May 2010
Location: Boise ID
Posts: 10
So next two things I am going to try are the icm and do a fuel pressure and ill update then. Any other help would be greatly appreciated. Thanks!

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Old 05-05-2013, 10:34 AM   #3
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Join Date: Feb 2012
Location: Raleigh, NC
Posts: 429
I always like to start w/ the basics: compression test, basic electrical, etc. If you have poor compression, then it will be next to impossible to get it to run correctly.

You shouldn't have a rich condition w/ the new carb if it is set up right. The stock carters are notorious for plugging up & conking out at idle, but the MCs will idle down to 500, smooth as silk.

The ICM is a possibility, but they usually just go out.

Fuel pressure should be fine if you kept the return line to the tank (that bleeds off excess pressure).

Have you checked all the grounds in the engine bay? You may be getting a very weak spark at speeds not high enough to trip the alternator into charging. I'd freshen up all your contacts on the battery, cables & ground wires...especially the ones connected to the engine & charging system.
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Old 05-05-2013, 10:44 AM   #4
Join Date: Aug 2011
Location: north of St.Franisville La.
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put a vacuum gauge on it and adjust the low speed needles, if that's not it check the power valve.
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Old 05-06-2013, 10:14 AM   #5
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Join Date: Oct 2011
Location: Layton UT
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Check the timing too, of it was not set right when it got Nuttered, or slipped it can cause a bad idle.
If you choose to say "plz" because it is shorter than "please" I choose to say "no" because it is shorter than "yes".
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jeep yj rough idle rich

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