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99' Wrangler Sport Bucking and Shaking

Diegoval0812

New Member
May 13, 2019
3
South Florida
I have a 1999 Jeep Wrangler Sport 4.0L 6Cyl. Whenever I am accelerating from a stop it will start bucking and shaking like if it was going to stall out. This only happens when accelerating from a full stop. When I first turn the car on in the morning, it accelerates fine for the first few stop signs and red lights but then it starts doing it at every single stop. Once it picks up speed the ride is smooth and has no issues.

I have replaced the distributor cap, rotor, cables, spark plugs, camshaft and crankshaft sensor. Any suggestions as to what the problem could be?

Thank you,
 

Jerry Bransford

TJ Guru
Supporting Member
Nov 9, 2015
10,641
Escondido California
This is the answer I gave you several hours ago to another of your posts on this elsewhere....

Since this problem apparently only starts once the engine has warmed up, that's almost assuredly caused by a bad upstream O2 sensor which is the one used to set the air/fuel mixture. The downstream O2 sensor only monitors the catalytic converter so it'd have nothing to do with this problem so if you decide to replace it, you can just replace the upstream sensor. The computer doesn't refer to the upstream O2 sensor for setting the air/fuel ratio when the engine is cold, it uses a preprogrammed table then. It only starts using the upstream O2 sensor for that job once the engine and O2 sensor have had a chance to start warming up.

If you decide to replace it, make sure to ONLY install an NTK brand sensor. Bosch O2 sensors don't work properly in our Jeeps.
 
Last edited:
OP
D

Diegoval0812

New Member
May 13, 2019
3
South Florida
This is the answer I gave you several hours ago to another of your posts on this elsewhere....

Since this problem apparently only starts once the engine has warmed up, that's almost assuredly caused by a bad upstream O2 sensor which is the one used to set the air/fuel mixture. The downstream O2 sensor only monitors the catalytic converter so it'd have nothing to do with this problem so if you decide to replace it, you can just replace the upstream sensor. The computer doesn't refer to the upstream O2 sensor for setting the air/fuel ratio when the engine is cold, it uses a preprogrammed table then. It only starts using the upstream O2 sensor for that job once the engine and O2 sensor have had a chance to start warming up.

If you decide to replace it, make sure to ONLY install an NTK brand sensor. Bosch O2 sensors don't work properly in our Jeeps.
Jerry,

Yes that was in another site. I posted my issue on different sites to get input from different people. I will go ahead and switch this out and see if it helps. Thank you for your input.
 

dudehitt

TJ Enthusiast
Feb 5, 2019
276
Phoenix
Hold on a second! There are other sites? Why wasn't i informed?

Oh wait, maybe you're talking about the ones that are almost impossible to navigate with a phone.

Seriously, i know a lot of the OG here came from those sites, but to me Chris has created an easy to navigate, simple to understand site with a lot of great minds.

I really don't go anywhere else.

/threadjack (it's been a minute, hope i did that right)
 

AndyG

TJ Addict
Supporting Member
Jul 30, 2018
2,490
Alabama
Jerry,

Yes that was in another site. I posted my issue on different sites to get input from different people. I will go ahead and switch this out and see if it helps. Thank you for your input.
Jerry is everywhere. You can’t hide . Don’t make him come to Florida and fix it .