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TJ bucks while driving down the road

Susan Kingery

New Member
Joined
Sep 11, 2019
Messages
11
Location
Gallipolis oh
We have a 2002 Wrangler 4 cylinder. We have an intermittent problem. I hope i can explain it so you can understand. We can be just driving down road at 55 and it starts bucking like you are in wrong gear. It smells like you are burning coal and blows black smoke. We have changed several parts with no success. Parts changed oxygen sensors changed twice, coil, plugs, wires, distributor, we even cut convertor off. No check engine light on. I may have missed a part or two that we have replaced. Please does anyone have any suggestions or ideas on what to do next?
 
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williambmac

TJ Expert
Supporting Member
Joined
May 5, 2019
Messages
3,887
Location
Fucktard state of NJ
Is the same concern that you have been having since your original post from Sept 2019. If so, I would recommend taking it to a qualified technician. It seems you have been throwing parts at it in an attempt to fix the condition.
 

wheelman2925

Member
Supporting Member
Joined
Oct 29, 2018
Messages
50
Location
Warren, NJ
Black smoke could mean unburned fuel. Might be leaky injector(s). Your post says it happens at 55 and is intermittent. Although a 2.5 hardly cruises anywhere, excess fuel could be building up in the cylinders at cruising speed with comparatively less engine load. That causes incomplete burn leading to black smoke, like diesel bros rolling coal.

If there's significant excess fuel, please check for the oil for signs of gasoline dilution. It could could wash down the cylinders walls and thin your oil to the point of spun bearings etc.

Good luck
 

Shuttlesworth

TJ Enthusiast
Joined
Jul 29, 2020
Messages
142
Location
Upsate SC
Have you replaced any O2 sensors? or spark plugs? I had a similar issue when those items went out. If you do have new spark plugs, then you could check your wires and distributor.
 
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Shuttlesworth

TJ Enthusiast
Joined
Jul 29, 2020
Messages
142
Location
Upsate SC
no we didn't
It may not make a difference in your case. But if the sensors cause a code to be spit out by the computer, then you need to disconnect the battery over night to clear the codes and let the computer start a monitor on the new sensor.

I saw that on a thread a long time ago and I have done it ever since. I don't know for sure if that is necessary, but I haven't had any issues when replacing sensors.
 
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RMETeeJay

TJ Enthusiast
Supporting Member
Joined
Sep 30, 2019
Messages
994
Location
CO, USA
Even with no CEL, you might have some stored codes. If you don't have access to a code reader, the big auto parts chains will read them for you.

You said that you removed the catalytic converter? If so, the sensors won't be able to do their job. Does it run good when cold? Does the bucking only happen once warmed up?

Black smoke could be bad piston rings if it does it all the time. Does it only put out the smoke during bucking, or other driving conditions?
 

Fishtaco

TJ Expert
Joined
Sep 29, 2020
Messages
3,739
Location
Perth AU
Black smoke is running too rich, blue grey smoke is oil burning, white smoke is steam from water vapour.

You are blowing black smoke so for some reason your petrol is not being burnt correctly its either flooding at higher speed or your timing is out or both, I don't do vehicle computers or sensors so cant speak of them.

Look at your spark plugs for black carbon/ soot or wet from fuel. Put your finger in the tail pipe, if its not very black but still black then its only running rich at the higher speed, if its black and sooty then you are running rich, both indicators of timing or fuel issues along with the bucking.

If bucking only at higher speed it is "Hunting" for either fuel air or spark.
 
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