RPM bounces around at constant acceleration

[ridingthethugjeeps]

This issue is kind of hard to explain but sometimes at highway speeds if i’m not moving the pedal my RPMS will just start bouncing and the jeep acts like it doesn’t know when to go fast. I’ve replaced the TPS and the issue isn’t as severe as it was before but i’m still having the same issue. There was an issue where the RPMS would just die out randomly at highway speeds but you could usually pick it back up if you floored it. And even with the higher rpms there’s like barely any speed increase.

Issue Video

 

[srimes]

This issue is kind of hard to explain but sometimes at highway speeds if i’m not moving the pedal my RPMS will just start bouncing and the jeep acts like it doesn’t know when to go fast. I’ve replaced the TPS and the issue isn’t as severe as it was before but i’m still having the same issue. There was an issue where the RPMS would just die out randomly at highway speeds but you could usually pick it back up if you floored it. And even with the higher rpms there’s like barely any speed increase.

Issue Video

The sound isn't clear enough for me to tell if the rpm is actually bouncing or just the gauge. Assuming the tach is accurate, well, the good news is it doesn't look like an engine problem.

I'll let someone with more transmission knowledge chime in here.

 

[ridingthethugjeeps]

The sound isn't clear enough for me to tell if the rpm is actually bouncing or just the gauge. Assuming the tach is accurate, well, the good news is it doesn't look like an engine problem.

I'll let someone with more transmission knowledge chime in here.

you can feel it on the road while driving i know it’s not clear in the video lol sort of like the jump you feel when you accelerate suddenly

 

[macleanflood]

So I'd start with reading live ODB data.

You can use a fancy scanner or you can get a Bluetooth dongle and use the free Torque Lite app.

What you want to do is see if the cluster RPM is doing the same thing the PCM thinks it's doing.

You also can run an instrument cluster self test.

-Mac

 

[hear]

I'm not convinced that isn't the torque converter locking/unlocking.

 

[ridingthethugjeeps]

So I'd start with reading live ODB data.

You can use a fancy scanner or you can get a Bluetooth dongle and use the free Torque Lite app.

What you want to do is see if the cluster RPM is doing the same thing the PCM thinks it's doing.

You also can run an instrument cluster self test.

-Mac

OBD live data

this was during the bouncing on the cluster

 

[ridingthethugjeeps]

I'm not convinced that isn't the torque converter locking/unlocking.

How come?

 

[ridingthethugjeeps]

I thought it was the tps because the position to full speed was way less than it used to be on the pedal. also sometimes my rpms would jump a little bit then die down to normal rpms when i come to a stop.

 

[macleanflood]

OBD live data

this was during the bouncing on the cluster

And those spikes are consistent with the dash tach?

Definitely interesting.

-Mac

 

[ridingthethugjeeps]

And those spikes are consistent with the dash tach?

Definitely interesting.

-Mac

They appear to be yes.

 

[srimes]

How come?

The rpm changes don't correlate with speed changes, which means there's driveline slip. If it was locked together like a manual transmission they have to move together, no matter what you're doing with the gas pedal.

Best case scenario it's the torque converter, which is supposed to slip.

This is what worries me:

"There was an issue where the RPMS would just die out randomly at highway speeds but you could usually pick it back up if you floored it. And even with the higher rpms there’s like barely any speed increase."

Can you recreate it and get video? Stomp on the gas at highway speeds and get higher rpm with minimal speed increase?

 

[ridingthethugjeeps]

The rpm changes don't correlate with speed changes, which means there's driveline slip. If it was locked together like a manual transmission they have to move together, no matter what you're doing with the gas pedal.

Best case scenario it's the torque converter, which is supposed to slip.

This is what worries me:

"There was an issue where the RPMS would just die out randomly at highway speeds but you could usually pick it back up if you floored it. And even with the higher rpms there’s like barely any speed increase."

Can you recreate it and get video? Stomp on the gas at highway speeds and get higher rpm with minimal speed increase?

When the rpm died out it wouldn’t return when i stomped on it but would occasionally but the speed increase was not that significant.

RPM DROP

i don’t think it dropped out here but i was stomping on it

 

[ridingthethugjeeps]

When the rpm died out it wouldn’t return when i stomped on it but would occasionally but the speed increase was not that significant.

RPM DROP

i don’t think it dropped out here but i was stomping on it

would only pick up rpm if i let my foot off the gas and back on

 

[DirtDawg]

No further replies in 4 hrs, so I'll chime in...

First off, your profile indicates 18 yrs old. If so and if this TJ is your very first vehicle - nice choice!

As to the described and shown symptoms, I tend to agree (as a non-expert) with @hear that it's transmission related. My own 2005 TJ purchased 4+ mos ago was purchased with no service history and had sluggish power "delivery". It upshifted smoothly but took too much throttle pedal for downshifts - unless lifting off and back on the gas as you've mentioned. Do you know prior related service history on yours? How does the trans fluid look? Mine had no pink dye remaining whatsoever and was fairly dark. As part of a long list of deferred DIY maintenance projects, I lowered the trans support (Rubicon Express belly skid), dropped and drained the trans pan, replaced with Dorman's equipped with drain plug plus a new Mopar trans filter, followed by refill of the trans pan with ATF+4 (prox 4 qts) plus flushing the torque converter (much more than 4 add'l qts until "pink" using the forum method outlined elsewhere). The thick goop on bottom of that pan was nasty, however only a bit of metallic particulate was evident in the sludge and magnet and with no "chunks" (didn't cut open the filter for inspection). Now a few hundred miles later, downshifts come much sooner and smoothly, without excessive throttle pedal "coaxing". I'm reasonably certain my DIY trans service was the first in 91k total miles. As miles continue to accrue, I'm hoping accumulated varnish on valve body components and solenoids will slowly dissolve. I'm not expecting "like new" functionality on a highly modified trail rig which has clearly seen lots of big rock action, however incremental improvements will be appreciated.

So then, depending on what's known (or not) on yours, perhaps consider the above during diagnostic evaluation...

 

[ridingthethugjeeps]

No further replies in 4 hrs, so I'll chime in...

First off, your profile indicates 18 yrs old. If so and if this TJ is your very first vehicle - nice choice!

As to the described and shown symptoms, I tend to agree (as a non-expert) with @hear that it's transmission related. My own 2005 TJ purchased 4+ mos ago was purchased with no service history and had sluggish power "delivery". It upshifted smoothly but took too much throttle pedal for downshifts - unless lifting off and back on the gas as you've mentioned. Do you know prior related service history on yours? How does the trans fluid look? Mine had no pink dye remaining whatsoever and was fairly dark. As part of a long list of deferred DIY maintenance projects, I lowered the trans support (Rubicon Express belly skid), dropped and drained the trans pan, replaced with Dorman's equipped with drain plug plus a new Mopar trans filter, followed by refill of the trans pan with ATF+4 (prox 4 qts) plus flushing the torque converter (much more than 4 add'l qts until "pink" using the forum method outlined elsewhere). The thick goop on bottom of that pan was nasty, however only a bit of metallic particulate was evident in the sludge and magnet and with no "chunks" (didn't cut open the filter for inspection). Now a few hundred miles later, downshifts come much sooner and smoothly, without excessive throttle pedal "coaxing". I'm reasonably certain my DIY trans service was the first in 91k total miles. As miles continue to accrue, I'm hoping accumulated varnish on valve body components and solenoids will slowly dissolve. I'm not expecting "like new" functionality on a highly modified trail rig which has clearly seen lots of big rock action, however incremental improvements will be appreciated.

So then, depending on what's known (or not) on yours, perhaps consider the above during diagnostic evaluation...

The trans fluid looked fine and it didn’t look low it was a bit dark and i’m not sure about the service history apart from me doing what was needed. I was thinking trans related as well but sometimes it’ll rough idle when i come to a stop.

 

[MikeE024]

If it’s your transmission, it could be the TC, the clutches, or an issue with line pressure.

I don’t believe it’s going in and out of lockup bc the RPMs don’t swing nearly that much for lockup. But that doesn’t mean your TC isn’t malfunctioning.

For diagnosing past 42RLE problems, I used the thinkdiag2 device coupled to my phone via their app. I chose line pressure (for each shift), RPMs (to track slipping), temp, and I tracked lockup. I then did a screen recording so I could review and share the results with the reman folks who I got the transmission from. Having this info will tell you if the problem is or isn’t a line pressure issue or an issue with the TC staying in lockup.

Also, my billet TC has been acting up, but I have never seen the RPM jumps like you see even under load in boost going down the highway. I feel shudder going into OD and when in lockup, and I have abnormally high heat especially when on the highway. Are you getting any shudder vibrations in your gas pedal when you are shifting into 3 or 4, or when driving on the highway?

 

[David Sheahan]

Hello hoping to see if potentially I'm having the same issue as the original post? Biggest difference is my RPMs are stuttering when I'm accelerating from a stop. But once i get to 45-50 mph the jeep runs smooth. The jeep did the RPM studder same as in the videos i posted but the lights that say the mileage of the vehicle was getting brighter and dimmer and the jeep eventually died, but i started it immediately after and the jeep started right up and seemed to drive a little rough when i limped it through a neighborhood to a family members house. I just got done replacing the torquer converter (the whole transmission was rebuilt in 2020 by a shop i know so I'm pretty confident in the rebuild). The wires coming out of my cutch solenoid in the transmission were bare so i put liquid electrical tape over them (hoping to fix it without taking the transmission apart). Seeing if anyone has any ideas? I'm thinking one of the three sensors that connect to my throttle body?

 

[David Sheahan]

^^^ update found out the connector to my fuel pump was barley connected so the jeep was starving for fuel