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Bad Transmission?

alexgalexg

NAXJA Forum User
Location
Connecticut
So I just got back from a long road trip. I noticed while driving up the mountain roads the Xj was bucking. I was not manipulating the pedal to keep it in a higher gear and I have been driving these Jeeps for many years now. They dont buck, at least not that I have ever managed to make it do and definitely not at 45 mph. I have not managed to get it to buck on the lower gears but in 4th if I am on any kind of incline it bucks. I checked the fluid and its at a good level, and the color is not red but its not black. Due for a change yes but not harmful for the transmission yet. Any way of fixing this problem? I need to avoid a new trans as much as possible. I have the ability but dont have the time or tools to swap it.

Oh I checked the transmission fluid after the vehicle had sat overnight. I thought that would be the best way of doing it. If thats the wrong way let me know.
 
AW4s are pretty solid. Drop the pan, change the filter, clean the pan, reinstall, and fill with the correct fluid.


However...are you sure it isn't a misfire? Ignition system misfires initially show up under high load in higher gears. 4th gear climbing a hill without downshifting and at low (under 3k) tpms is a very likely time to notice a misfire.
 
Checked after it sat? To check tranny fluid, in any auto, first get it to operating temp. Then, while at a stop, shift it from park, through all the gears(allowing them to engage), then back. Pull the dipstick, wipe it, stick it back in, check it.

I'm not an expert on the AW4, I'll let someone else chime in there.
 
Does not seem like a misfire. I derived the timing on that engine myself, has a new engine. The only sensor I replaced is an o2 though. Are you suggesting that the ignition coil may be going out? Also worth mentioning I have never actually reached 3k on my Jeep so its always at these low rpms
 
Checked after it sat? To check tranny fluid, in any auto, first get it to operating temp. Then, while at a stop, shift it from park, through all the gears(allowing them to engage), then back. Pull the dipstick, wipe it, stick it back in, check it.

I'm not an expert on the AW4, I'll let someone else chime in there.

I will try that thank you. Definitely did it the wrong way
 
Does not seem like a misfire. I derived the timing on that engine myself, has a new engine. The only sensor I replaced is an o2 though. Are you suggesting that the ignition coil may be going out? Also worth mentioning I have never actually reached 3k on my Jeep so its always at these low rpms
An ignition induced misfire does not have anything to do with the timing, it actually means that one of the sparks is not making it to the spark plug or not jumping the spark plug gap because it is too weak. This can be caused by a loose plug wire boot at the plug, a loose plug wire boot on the distributor cap, a carbon track down the porcelain of the plug, a fouled spark plug from oil burning, a broken spark plug wire or damaged spark plug wire, a bad distributor cap or rotor, bad distributor shaft bearings, etc, etc, etc, the list goes on.

It's is easiest to diagnose if you've felt it before. You can intentionally create a high load by letting it shift into high gear, then steadily increase throttle pressure (not so hard as to cause a downshift). Usually this is done going up hill.

If you have a misfire it will feel like the engine shuts off instantaneously, and then comes right back to normal. You feel that "sputter" repeatedly if you keep the load high. Either downshifting to raise the rpm, or backing out of the throttle will cause the misfire to stop and it will run normal.


On a side note...why has your jeep never been over 3k rpm? Even new motors need to run the full rpm range to break in properly.
 
It sounds like it should be down shifting and is not. I would also suspect it is knocking, pre ignition under heavy load at too low of an rpm. I do not think a miss fire would could cause bucking (I could be wrong, I guess if the TC is locked even a miss fire might buck.)

What it sounds like for sure, is that it is not unlocking the TC and down shifting when it should to increase the torque enough.... If the TC is not locked, it should not buck even with a miss fire, (I think)

TPS????

What exactly does this mean?

" I derived the timing on that engine myself,"
 
What exactly does this mean?

" I derived the timing on that engine myself,"
This means that when I put the engine in it had no distributor. I put one in so I know its not off.

As to answer the questions about the sputtering and whatnot... The engine does not change in rpm level what so ever during this process. During the time that it is bucking you can only feel the vehicle bucking. No change in rpm and the engine runs smooth as can be. I would know if it ran even slightly different since it has a loud high flow exhaust.

As far as the plugs and leads go I have looked them over since this has started. All new and all good.

Im not sure if this helps but being a 98 it has the HO system. HO Jeeps tend to start within a crank or two but this one starts more like a renix Jeep. Five cranks to fire up. Already checked for fuel leaks and pump is good I know how to do all that stuff.

Engine has actually been over 3k but only maybe 10 times when emergency accel has been needed. So it has done like 95mph and once a burn out when an emergency occurred. But I dont need it to shift past 2k to accel faster than average traffic not to mention I baby it.

I am not very good with diagnosing sensors because the only one that has ever given me trouble was a cps on a friends zj so I am not sure if the tps could cause any of this or not.

Hope this is enough info, tried to break it up to make it easier. Thank you all.
 
Depends a bit on the severity of the mis, but most of the time I can feel a mis regardless of gear or TC lock.

If the TC is not locked, the TC fluid slippage should not allow it it to buck, at all.

There is a difference between an engine miss-shake, and an entire drive train bucking. It feels very different.

If it is in gear with a clutch engaged or the AW4 TC is locked, yes an engine miss can cause bucking.
 
Maybe just not enough fluid getting in and I need to add more? I will see tomorrow after work. When I come home and the engine is running and hot after the commute I can check the levels. If its low I will flush the whole thing
 
I would investigate why it is not down shifting on its own, unlocking the TC, down shifting to 3rd, and then re-locking to raise the RPM due to the higher torque load going up the grade. I had that problem ages ago, but the solutions were bits and pieces of many things wrong with it (it was, is a Renix).

I had the problem with my low HP diesel (64 HP tops, LOL), 85 custom XJ, and always had to down shift to solve it climbing grades.

Have you done the Transmission cable to throttle body adjustment yet? There is an entire thread on that super simple step and how huge the effect and difference in performance is on here in this section.

Then after that, the TPS may be an issue. I drove my 87 for 13 years before I discovered this year that the throttle cable rod was bent and cheating me out of 1/3 of the beasts peak power ability at a fixed gas pedal position. I had. have 3 rigs, and when the TPS data on my scanner was wrong, I compared the throttle rods and found the 13 old issue. I thought is was worn out engine LOL, 290,000 miles.

I'd ask some of the guys with later HO rigs about the vehicle speed sensors, etc that might affect shifting, because I suspect from what your saying on going up a grade, you need to be in 2200 to 2600 rpm range or higher....in 3rd gear. Mine does 2000 rpm in 4th at 55-60 mph on flat runs.

Something in the controls is not telling it down shift I think.


So do I need a new TC then? Or what are some options to repair this problem
 
My other Xj is a 99 and has done 300k downshifting at the same speeds and conditions this 98 does but didnt buck. I still think its worth my time to investigate but as I said it has always shifted this way and so has my 99 with no bucking. But yes it very much feels like the transmission is what is bucking not the engine. I can feel it coming from that area and not the engine not to mention the engine always runs smooth.
 
If the TC is not locked, the TC fluid slippage should not allow it it to buck, at all.

There is a difference between an engine miss-shake, and an entire drive train bucking. It feels very different.

If it is in gear with a clutch engaged or the AW4 TC is locked, yes an engine miss can cause bucking.
I was merely giving an option based on my experience...you wouldn't believe how many customers use the term "buck" to describe a misfire.

This is the problem with Internet diagnosis...everyone describes symptoms differently.
 
Have you considered making a video of what's happening? Post it on YouTube and we could check it out?

Also, if it downshifts similarly to your other jeep...then it seems unlikely that downshifting is an issue.

Am I correct in assuming you do not have a check engine light on? Do you have access to a scantool that can check misfire counters? That would be an easy way to rule out one possibility.
 
I can borrow a scan tool hopefully tomorrow to check it out. I can make a video for you all. In fact I recently started making repair videos for Jeeps in my spare time so I can just upload it to that channel. It is likely not going to show on video when it is "bucking" though because the engine runs smooth and as it should the entire time. But I can show you the speed and rpm so it may help.

Likely unrelated but favor needed
Someone noted that the brand new o2 upstream could be bad despite no check engine light and the fact that it is only a matter of months old. I really doubt it is bad because it seems like a quality sensor however I only replaced it because the wire had gotten torn off the sensor after off roading. Driving with a non working o2 sensor feels more like a hesitation or a car with a small carb issue feels like but only on occasion. It felt nothing like what I am talking about here. I only bring it up because the plastic connector was broken. I was very careful to make sure the o2 four pins got installed the correct way when I put it all together. But if anyone has detailed pics of the connector on a 97-99 xj for me to be sure just email me [email protected]
 
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I can borrow a scan tool hopefully tomorrow to check it out. I can make a video for you all. In fact I recently started making repair videos for Jeeps in my spare time so I can just upload it to that channel. It is likely not going to show on video when it is "bucking" though because the engine runs smooth and as it should the entire time. But I can show you the speed and rpm so it may help.

Likely unrelated but favor needed
Someone noted that the brand new o2 upstream could be bad despite no check engine light and the fact that it is only a matter of months old. I really doubt it is bad because it seems like a quality sensor however I only replaced it because the wire had gotten torn off the sensor after off roading. Driving with a non working o2 sensor feels more like a hesitation or a car with a small carb issue feels like but only on occasion. It felt nothing like what I am talking about here. I only bring it up because the plastic connector was broken. I was very careful to make sure the o2 four pins got installed the correct way when I put it all together. But if anyone has detailed pics of the connector on a 97-99 xj for me to be sure just email me [email protected]

Now I'm even more convinced it's your O2

NTK only.
 
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