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Discussion Starter · #1 ·
my 97 tj 4 cyl runs great until traveling speed or you push on the gas a little more to climb an incline it has a misfire or a chugging feeling. i have replaced the coil, distributor, cap n rotor, plugs n wires. i also replaced in tank filter/regulator, idle air control valve, intake air temperature sensor. ive ran tons of injector cleaners through it an also cleaned the throttle body. it also runs a little rough at idle it has no lights on n no codes any help would be great
 

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Is the automatic downshifting when you try to climb the kind of grade that is making your engine stumble? If it doesn't downshift, what happens if you manually shift it to 2 on steep grades?
 

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Discussion Starter · #5 ·
it does downshift and cleans right up it only does it around 2000 rpm doing 45 to 55 cruising speed if you give it a little more gas it skips a little more but if you step on it to pass a car it runs great
 

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What size tires are you running? And has your upstream 02 sensor ever been replaced?
 

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Discussion Starter · #7 ·
it has 31s on it and no it hasnt been changed everyone i talk to said if they were bad it would send a code and i hate to guess anymore i just bought the jeep
 

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Discussion Starter · #8 ·
everything i have done has given it a lot more power so it hasnt been a complete waste
 

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A bad upstream (nearest to the engine) 02 sensor won't necessarily always generate a code, early TJ computers weren't that sophisticated. A bad 02 sensor can trick the computer into thinking the air/fuel mixture is too lean (sometimes too rich) so the computer will start screwing up the fuel mixture.
 

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Discussion Starter · #10 ·
the spark plus are burning golden brown would the 02 sensor cause a misfire like that at cruising speed
 

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I just tried Jerry's suggestion from another thread about disconnecting the front O2 sensor and drive it to see what happens. Easy to do just unclip the connector from the harness.
Guess what? The stumbling sputter I used to get is gone.
Yes it threw a CEL code and that I can clear up after I put in the new O2 sensor.
BTW it did not give me a CEL code before I disconnected it. Also with the sensor disconnected it really has more power but I will get a new sensor tomorrow anyway.
 

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Discussion Starter · #13 ·
i tried unhooking the 02 sensor it only made the problem worse so i hooked it back up and cleared the code
 

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does it hesitate on turns to? Might be water in the gas sloshing around and getting sucked in. Have you ever used drygas? Its a liquid that obsorbs water to be burned better... might be worth a shot.
 

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Discussion Starter · #15 ·
yes i have tried treatment many times dry gas and fuel system cleaners also changed in tank filter/regulator it has a poly tank so its not full of rust either
 

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Discussion Starter · #16 ·
i was reading on the internet that the tps can cause the same symptoms so i replaced it with no luck it does seam to act up more when u drive it for a while. guess a little more an everything will be new.
 

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I still have the same problem. I posted earlier that changing the O2 sensor made it better. Well, that did not last one day and my 4.0 is still surging as before. New plugs, rotor and wires as well as new TPS and still the same problem.???
 

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Discussion Starter · #18 ·
i ordered a new fuel pump n strainers hopefully will fix the problem their isnt much left that i havent changed so i will let you know the outcome when i get the pump in i already put a new filter/regulator in so everything in the tank will be new
 

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I don't understand how the fuel pump could be bad at low speeds but fully adequate at high speeds under load.
I'll wait to see if your fix is the answer. Please post your solution.
 

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Discussion Starter · #20 ·
i dont understand that either but i talked to several mechanics for jeeps and they said the fuel pump can do that i have changed pretty much everything else so it is possible it should come in the mail tomorrow or the day after so i will let you know as soon as i install it
 
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