4.2 L engine trouble - JeepForum.com
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Unread 09-26-2001, 07:47 PM   #1
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Join Date: Sep 2001
Posts: 23
4.2 L engine trouble

1990 YJ 4.2L Carb'd. It will run OK, then next time it may not. It will sputter badly between 1,000 and 2200 RPM and the cat will glow red hot. Sometimes it wont even start for an hour or longer, then it decides to run again. I am stumped! Put in new plugs, wires, cap, rotor, fuel filter, coil. Also checked timing. All the wiring seems good. Also changed pickup coil in dist. Maybe o2 sensor or cat? Please help if you can. EMail for more details MGcsl@aol.com

90 YJ 4.2L
4" procomp lift
33x12.5 ProComp Mudders
Looks Great, Runs Horrible!
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Unread 09-26-2001, 08:35 PM   #2
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I'm thinking its the cat. I need a new cat too and I know its robbing tons of power and makes the motor idle bad. Considering its glowing red hot I'd say thats your problem. I would also check your O2 sensor because that may be the root of your problem. So you're looking at a new cat and maybe a O2 sensor if thats bad also.
1992 YJ, 2.5L 4-banger, 2" Lift, 31x10.5 BFG Mud Terrain, K&N Filter, Restrictor Removed, Hi-Lift, Custom bumpers, More to come...
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Unread 09-27-2001, 08:31 AM   #3
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Welcome to the world of 4.2's Itès never going to run perfect but yours definately sounds worse than it should be. Given the symptoms I would have to agree with JeeperJay. A red hot cat sounds like you need a new one. Might as well change the O2 sensor as well, if you have never changed it before chances are that it is the original.most of us skip over the O2 sensor during regular tune ups. Jeep should run great (as good as our carbs will let it anyway)after those are replaced.

good luck
90 YJ...Stock for now.
74 Dodge Dart Sport
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Unread 09-27-2001, 09:46 PM   #4
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1988 YJ Wrangler 
Join Date: Nov 2000
Location: Calgary, AB
Posts: 6,879
Why change the cat .. pull it out and straight pipe it .. much better for power and fewer problems for your Jeep.

I am running cat-free right now!
Hello, my name is Vance and I am a Jeepaholic.
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Silver 2006 TJ Unlimited, zombie ready as the daily-driver

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Unread 09-27-2001, 10:41 PM   #5
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When your catalytic converter is red hot, that is an indication that it is trying its best to clean up an exhaust stream that is very rich with a lot of extra unburned gas going through it....I think your real problem is in the Carter BBD carburetor.

Pull out a spark plug and look at the end. I bet it is real black and sooty. If this is the case, you need to look at the carb as the real source of your problems.

Unfortunately, getting this carb to run halfway decent is a real pain. Unless you have many years of carb experience, identifying the problem is best left to the experts. Do you have a good independent carb shop in your area?

I have a carb rebuild kit on my bench, and will be rebuilding my carb in the next few weeks... My problems include bad idle ( dies at stop signs) and hard starting ( cranks for 20 seconds before starting cold because the choke will not close)..

These computer controlled carbs are real pieces of key wrap, no wonder they went to fuel injection...
Jeeper Bill
88 YJ, 4.2L, 5 Sp
2.5 In RE Lift
31" BFG AT KO's
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