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Discussion Starter · #1 ·
My '05 TJ 4.0 engine has started jumping/bucking on acceleration. Only does it from a stop, moving very slowly, or on an incline (so under a load) does not do it if I rev it in neutral. RPM does not change when it happens. Hot or cold does not make a difference. No CEL codes are thrown.

What I've tried so far,

  • Seafoam in the tank, vacuum line, and throttle body. Twice.
  • Checked Spark Plugs
  • Checked Coil Rail
  • Ran without 2 - Pre-Catalytic Converter O2 sensors (to see if CAT was clogged, It was not)
  • Replaced 2 Pre-CAT O2 Sensors
  • Reset PCM
  • Deoxit in PCM connections
  • Unplugged horn relay
  • Unplugged TPS
  • Unplugged MAP sensor (got better), replaced MAP sensor and it came back

Any help at all would be great, this issue is starting to get very aggravating. Could it be a sign of a shorted PCM?
 

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Those pre cat upstream sensors are critical for mixture and removing them is not a way to test for obstruction of pre cats
 

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Discussion Starter · #3 ·
I was told by a mechanic in my club that it would be ok to take them out for a short run. Just long enough to see if the CAT was clogged. I'm definitely not running without them. :)
 

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But if you make it run like crap how can you tell if it runs like crap because mixture is way off or because of an exhaust obstruction
 

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Not to sound harsh but I must concur with Digger84. You are way off! Do yourself a favor and make a check list. Stay with the basics first. You said you checked spark plugs yet you don't say how many miles are on them! Spark plug wires ? Also if you have done the basics. You can check online I'm confident you can find a test pipe that will allow you to temporarily remove the cat.
 

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Hello. New Jeep owner here. Bought my '05 TJ (which I hopes means the "Unlimited" extended wheel base edition) in November of last year.

This morning, my Wrangler started doing EXACTLY what is described here. Shifting into first, out of first into second the car starts bucking and jumping. Once I shift up to 3rd and beyond (I have the manual 6-speed mated to the 4.0 liter engine) the bucking stops.

I've no idea if its the tranny, the clutch....or anything else.

Any more ideas?
 

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Discussion Starter · #8 ·
It actually happens just below 2000, only if I get on it quickly. If I ease into it it doesn't do it.
 

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I did this for a bit while in first from a stop, especially if about to go up an incline. Then I realized it was just me relearning how to drive stick after not driving stick for 15 years. Problem solved now. But the gear ratio in 1st for me is so high that it doesn't take much gas for me to buck in 1st. If that makes sense. I either have to give the Jeep a lot of gas in first or ease off the clutch slowly. I don't claim to be a mechanic so don't take this as more than just a personal scenario for me.
 

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I would have to agree with Doe above. This post is all over the place. Are we talking engine bucking? or are we talking clutch or tranny issues. You need to start with the basics. If its engine related I would start with a tuneup. Personally you don't check spark plugs you replace them. Does this bucking occur when wet outside or all the time. So many issues can be easily resolved but you need to start with the basics. A lengthy explanation of the problem can help us help you.
 

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Discussion Starter · #11 ·
Sorry haven't been on here in a bit. I am talking an engine issue not trans. Two updates on what I've tried with interesting results.
- I did a hard reset on the PCM by disconnecting the neg battery lead, then disconnected the PCM and left it off for an hour. After that the problem only happened when I gave it a lot of gas. So it got better, but still didn't completely go away. I then left it disconnected overnight and the problem came back. I inspected the PCM closer and noticed a small burn mark as if a wrench hit the PCM while disconnecting the positive terminal. Which is why I'm starting to lean toward the idea that the PCM was shorted.

- Another test with interesting results was that I disconnected the MAP sensor and the problem went away. It ran a little rough but not the same issue, obviously because the MAP was disconnected. The MAP sensor on it now is a new one, and I tested it with a multimeter and everything looked normal. Plugged the MAP back in, problem returns.
 

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Discussion Starter · #12 ·
It's been about a week and the bucking has not come back. I was planning on changing out my battery cables for a while. I finally got time to do it, and it turns out that that might have been part of the problem. I guess either the PCM or sensors or a combination of may have not been getting the correct amount of power. But as of right now, it SOLVED the problem.

I guess you can add battery cables to the long list of possible fixes for this issue ;)
 

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@dcguitars, did the problem ever return? I'm having a bucking problem, but it's only there under normal and slightly hard acceleration. Easy acceleration and hard acceleration either mask the problem, or it's not there.

I'm troubleshooting.
 

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There are a number of threads in WF that pertain to this condition, and they ALL, every one specifically say, " Do All The Basic Checks First!"
 

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My '05 TJ 4.0 engine has started jumping/bucking on acceleration. Only does it from a stop, moving very slowly, or on an incline (so under a load) does not do it if I rev it in neutral. RPM does not change when it happens. Hot or cold does not make a difference. No CEL codes are thrown.

What I've tried so far,

  • Seafoam in the tank, vacuum line, and throttle body. Twice.
  • Checked Spark Plugs
  • Checked Coil Rail
  • Ran without 2 - Pre-Catalytic Converter O2 sensors (to see if CAT was clogged, It was not)
  • Replaced 2 Pre-CAT O2 Sensors
  • Reset PCM
  • Deoxit in PCM connections
  • Unplugged horn relay
  • Unplugged TPS
  • Unplugged MAP sensor (got better), replaced MAP sensor and it came back
Any help at all would be great, this issue is starting to get very aggravating. Could it be a sign of a shorted PCM?
 

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I have an 05 Wrangler with 4.0 engine. Was having idle surge issue that would not resolve after replacement of various parts and no code was given.

Jeep has Service Bulletin for my issue and is covered for life of vehicle. Check Jeep Service Bulletin 25-005-13

Hope this helps someone.
 

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I have an 05 Wrangler with 4.0 engine. Was having idle surge issue that would not resolve after replacement of various parts and no code was given.

Jeep has Service Bulletin for my issue and is covered for life of vehicle. Check Jeep Service Bulletin 25-005-13

Hope this helps someone.
Welcome to to Forum, from Cave Creek AZ.
 
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