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Savvy/Currie Aluminum Control ArmsRockridge 4WD IS Taking Zone Offroad Suspension Lift Kits ZONE 4.25" combo lift for TJ available at Rockridge4w

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Unread 08-20-2011, 07:37 AM   #1
19renegade91
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ahhh!?!?

hello ,my g/f bought a yj a few months back 91 renegeade 4.0l ho 5 spd
since she has had it i have done rear brakes, starter, exhaust, cold air intake, stereo, 3 oil changes and fuel filter and other things im sure. the engine runs starts and drives GREAT but as soon as you go past half throttle approaching full throttle or full throttle it stumbles over its self over and over and over uuntill you let off the gas and accelerate with less throttle. the speed doesent matter, i could be taking off from a stop and put pedal to floor and it doesent accelerate it just bog bog bog bog bog and you can hear it in the exhaust too, it runs perfect idles great and everything but full throttle kills it...and yesterday i could use full throttle...today i cant even use half..please help me, i was not hard on the engine and the engine has 150k
please help me !

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Unread 08-20-2011, 07:49 AM   #2
19renegade91
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when it hesitates backfiring or whatever it does under full throttle it is a fast paced sound ..with the rpm that the engine is at like a military drum, quickly.....lkike buzzing your lips ...dadadadadadadadada untill you let off the gas a little
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Unread 08-20-2011, 07:59 AM   #3
No-Doors
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You described what happened with my F-150 about a year ago. I cleaned injectors, fuel filter, air filter, spark plugs; you name it. Thought it was tranny prob, so took it to a bud who is tranny expert. Took him for a test drive and it took him about 10 seconds to tell me my Cats were clogged; He was right. May/May not help, something to consider.
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Unread 08-20-2011, 08:32 AM   #4
oldtime_ironman
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Yeah, check the cat converter. If you bang on it and it rattles, its bad.
I would clean the injectors
Also take a look at
Throttle position sensor
MAP sensor
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Unread 08-20-2011, 08:38 AM   #5
Tom95YJ
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It sounds like a bad catalytic converter to me. I'd replace it and go from there.
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Unread 08-20-2011, 08:49 AM   #6
19renegade91
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really a bad cat haha,....will it stink if it is clogged? i have noticed bad cat smell latley when under load, but now i cant put it under load....like i said it runs fine you can rev it up in neutral but the more load the more it wont go....like the rpms wont even climb when it happens ...sounds like a rev limiter on ken block racing car exept its when i full throttle while driving and it will not climb i must release gas pedal and or downshift to accelerate
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Unread 08-20-2011, 09:35 AM   #7
Skydmark1
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I'm thinking bad cat or bad TPS
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Unread 08-20-2011, 09:37 AM   #8
No-Doors
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Quote:
Originally Posted by oldtime_ironman View Post
Yeah, check the cat converter. If you bang on it and it rattles, its bad.
Mine had gotten so clogged it wouldn't rattle anymore.
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Unread 08-20-2011, 10:39 AM   #9
NonRubicon
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Agree on the cat being the culprit, especially if it looks OEM. I recently replaced the 21 year old OEM cat on mine. It didn't rattle though because the busted off piece of the catalyst was lodged sideways in the outlet. Discovered the clog when I was replacing the cat-back exhaust. I too had bog and an invisible brick wall that I couldn't accelerate past. New Magnaflow cat => problem solved.
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Unread 08-20-2011, 10:44 AM   #10
NicksYJ
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If you cant tell if the cat is clogged by wacking it, and it isn't terribly rusted try removing the clamps and removing it (right before the muffler) and see if the jeep continues with the same problem
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Unread 08-20-2011, 11:30 AM   #11
jeep108
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Quote:
Originally Posted by NicksYJ View Post
If you cant tell if the cat is clogged by wacking it, and it isn't terribly rusted try removing the clamps and removing it (right before the muffler) and see if the jeep continues with the same problem
For diagnostic purposes only of course.............
Get back you tree huggers back I say
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Unread 08-20-2011, 01:51 PM   #12
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Originally Posted by jeep108 View Post
For diagnostic purposes only of course.............
Get back you tree huggers back I say
I ain't no tree hugger... But when I can't ****ing breathe because some fool took his cat off and his tailpipe is spewing out death, then it really bugs me.
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Unread 08-20-2011, 02:56 PM   #13
19renegade91
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just for refrence it doesnt depend on RPm at all, it depends how much the accelerator is pushed. if the cat was clogged wouldnt you smell it pretty badly? i dont smell cat at all , the cat is original... i can be in first gear or fiftyh gear it doesent matter soo as 3/4 to wide open throttle it sounds like a drone dadadadadadadda and doesent pick up rpm at all it stays stuck where it is ...i can still accelerate pretty good using half throttle but im concerned....is my fuel pump going bbad...fuel filter is new, i know i can hear it in the exhaust but there is a glass pack after the cat afterall amplifying the sound but i know i can hear it,
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Unread 08-20-2011, 03:14 PM   #14
No-Doors
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Its loading up on you. Mine done same thing; as long as I babied it, no prob; when I would romp on it the thing acted like it was running out of gas (starved for fuel). I had same thoughts as you; lack of fuel, but it wasn't. Best thing to do is check by disconnecting as suggested above or take it to a shop.
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A Rancher told me that back home he can drive his Jeep all day and not get off his own property; I said "I've got a Jeep like that too"!

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Unread 08-20-2011, 05:03 PM   #15
NonRubicon
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Quote:
Originally Posted by 19renegade91 View Post
...if the cat was clogged wouldnt you smell it pretty badly? i dont smell cat at all , the cat is original...
My cat didn't smell bad, but the exhaust smelled a little on the rich side due to the catalyst being damaged and my carb running rich.

From what I've read, you should be able to diagnose a bad cat by reading the temp with a IR thermometer. I've never done it myself though so I'm not sure what the temperature difference between the head pipe and cat should be. The cat should be hotter than the pipe running into it, but not too hot, because running too hot is also a sign that the cat is bad.

You can also just pull the muffler and look into the cat and see if there is any obvious damage or obstructions, or you can disconnect the cat from the head pipe (temporarily) and see if the problem goes away.
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