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Unread 07-31-2011, 12:31 AM   #1
riverhippy
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1991 YJ Wrangler 
 
Join Date: Jul 2011
Location: pic is my girlfriend/fiancee, mi
Posts: 240
im holding a gun to my head

91 yj, all stock, bypassed o2 sensor, bypassed mat sensor, changed tps, map, cap, rotor , plugs and wires and ran seafoam thru the carb. this is what started two weeks ago and still does after all ive done for her (as listed above) jeep runs great after its sat overnight. on hot days it will run good fro 20-30 mins then it starts to buck, backfire and lose power. wtf?

im decent mechanically but im ready to run the jeep over a cliff or kill my jeep...frustrated beyond measure

any help and ill ask my gf to give you a kiss.

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Unread 07-31-2011, 12:50 AM   #2
moonshinefuel
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1995 YJ Wrangler 
 
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Location: Los Angeles. California. United States.
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You have a carb on a 91? Also can you explain how you successfully bypassed the 02 sensor, and the other one?
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Unread 07-31-2011, 01:26 AM   #3
tankinyj
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carbed? check all your vaccum lines on the carb. had a problem similar to this on my 73 mustang recently. I thought it was vapor lock (fuel lines getting too heated causing the gas the evaporate in the lines before it even got to the carb), i got similar results like you did such as backfiring, bucking, popping, half stalling (engine stops for 1-2 seconds then roars back to life without restarting engine). it was as simple as a disconnected vaccuum line, reconnected it and voila, problem fixed. hope this helps
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Unread 07-31-2011, 04:02 AM   #4
MJMPC
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Hook all your sensors back up clear all the codes rum it for awhile and check them again let us know.

You dont have a carb you have a throttle body if you are working on a 2.5.
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Unread 07-31-2011, 07:47 AM   #5
oldtime_ironman
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1991 YJ Wrangler 
 
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Location: 14304 Niagara Falls, NY
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Here, have a cold brew and lay off the coffee some. There's no way your YJ has a carb unless somebody put it there. The 1991's were all EFI far as I know. You really need to hook all the sensors up and clear the codes out of the computer, which is easy to do - just unhook the battery! And then get back to us, relax and grab another cold one, and let us know.

Jeeps actually run a lot better with all of the sensors and EFI hooked up. Compared to carbs.

Last edited by oldtime_ironman; 07-31-2011 at 07:49 AM.. Reason: clarity
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Unread 07-31-2011, 09:49 AM   #6
ratmonkey
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Heat related? Coil or ecu.
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Unread 07-31-2011, 10:11 AM   #7
riverhippy
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i put a new coil on last year, but, ill test it. why would coil or ecu be heat related? ive had this problem even when its running in open loop mode. is there a way to test the ecu?
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Unread 07-31-2011, 10:26 AM   #8
4.7stroker
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Strange things happen with heat, you could have a intake leak when it heats up, your fuel pressure could drop, your cat could cause your problem. You are just going to get down and trouble shoot it and stop throwing random parts in it's general direction.

Dwayne
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Unread 07-31-2011, 10:30 AM   #9
riverhippy
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thanks dwayne. i appreciate your insight. ive tested for vac leaks while its running rough. none could be found. as stated earlier, fuel pressure is solid at 31. ive listed the parts ive changed so i could get better feedback. i didn't just start thowing random parts in as a guess. they either coded or tested bad and i still have the underlying problem. the reason i posted was to see what im missing in the trouble shooting.
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Unread 07-31-2011, 10:44 AM   #10
nembudonna
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Check your catalitic converter. I've seen them be the problem more then once.
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Unread 07-31-2011, 10:49 AM   #11
4.7stroker
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My apology for being rough, there are many that just throw money at a problem hoping it will go away.
What is the condition of your timing chain?
Does your compression stay the same?
Have you put a vacuum gauge on it to see what that is doing?
Does your distributor pick up read right?
Have you tested your CPS? removed, clean reinstall?
Have you gone through the wiring harness cleaning corrosion grease plugs and reinstall?

Dwayne
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Unread 07-31-2011, 11:11 AM   #12
riverhippy
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there is no cat converter.
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Unread 07-31-2011, 11:13 AM   #13
riverhippy
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1991 YJ Wrangler 
 
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Posts: 240
thanks dwayne. im bypassing sensors to avoid spending the cash on them unless they need replacing. vacuum is solid at 17. when i race engine it drops to 0, i assume that is normal (according to my repair manual) ill check rest of those today and repost. how do i check the timing chain without pulling cover?

reason for frustration is im 48 and my gf is 20. tried taking her to the beach 4 times but this prob keeps stopping us...gotta get it fixed...lol
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Unread 07-31-2011, 11:52 AM   #14
4.7stroker
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1988 YJ Wrangler 
 
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What is your altitude, a healty engine at sea level will produce 21"hg loosing 1" for every 1000' gain. I am at 5500' and pull 17" hg on a modified engine.
Either you have low compression or your timing is off.
Your CPS or distributor pick-up are prime suspects.
I would go the the JY and grab another dizzy and CPS to rule that out, you can snag them from a Cherokee, they will be the same.

Good luck with the GF hope you get to the beach
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Unread 07-31-2011, 02:09 PM   #15
riverhippy
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whole distributor? im 585' above sl. but the hg is good according to chiltons and other repair mans. ill check the compression, then the cps and repost..
the issue that keeps throwing me is this happens when its hot out. if i fire it up tonite it will run perfect. i just dont get what the heat has to do with this.
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backfiring , help please , loss of power , sputters , YJ

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