RPM Fluctuation

[RobbyD]

I haven't been able to find anyone with a similar issue to me in the threads. I have an 07 LTZ Hoe with the 5.3. I've run into an issue where until my oil temp hits about 190-200, while at about 10-25% throttle and at most any speed/rpm, I will get a 200-400 consistent up and down fluctuation in RPM.

No issues at idle or cold starts. Only when under load in the throttle position sweet spot (which is where I'm always at around town so the issue is frequent)

Once everything is warm the issue disappears or If I simply go over 30% throttle position (in most cases) it also goes away. Hopefully, that's enough info to find me some help. Any other info y'all need let me know.

I can also upload a video if that would help.

 

[Fless]

Use a graphing scan tool and compare the throttle position sensor value against the pedal position sensor values to see if, over various positions, 1) they compare favorably and 2) they're smooth and don't have any dropouts or glitches.

 

[RobbyD]

Use a graphing scan tool and compare the throttle position sensor value against the pedal position sensor values to see if, over various positions, 1) they compare favorably and 2) they're smooth and don't have any dropouts or glitches.

Definitely going to see if my scanner has that and if I can do that right now, but would that explain why it goes away at temp?

 

[Fless]

Not sure but you'd want to at least rule out any anomalies with those two working together. Maybe graph them both cold and hot to see if there's a significant difference.

When was the throttle body last cleaned?

 

[RobbyD]

IMG_3599

This is "IMG_3599" by Robby on Vimeo, the home for high quality videos and the people who love them.

vimeo.com

Here's a video of what's going on as well as some stats I was able to pull up on my limited scan tool. Nothing seems out of the norm, but please tell me if I'm wrong. I tried to keep everything as steady and consistent as possible. TB was cleaned this past summer.

Could this potentially be transmission-related? I have 230,000 miles, but the trans was just rebuilt at 200,000 just about 2-3 years back. I sure hope that has nothing to do with it.

p.s. Don't worry about my little yellow friend. Just throwing an evap code I'm choosing to neglect. P0446 and P0452 if it helps this situation

 

[B-train]

It almost looks as though the TCC isn't staying locked up. I couldn't read the scan tool on my small screen, but the 200 rpm fluctuations seem like that to me. Can you use tow/haul mode at the same speed and see how it acts? Maybe go to the next lower gear and observe as well.

 

[mikez71]

^^^ X2 ^^^

You said any gear any speed, does that include 1st gear? (1st does not engage TCC)
Second thought, it's more likely to slip in higher gears so testing lower gears might be inconclusive.

Try monitoring your TCC slip rpms. When TCC is locked while cruising, slip should be 0-40 rpms typically.
If you see it jump back and forth a couple hundred RPMS at steady cruise..

@NickTransmissions will know exactly what/how you should test..

 

[RobbyD]

It almost looks as though the TCC isn't staying locked up. I couldn't read the scan tool on my small screen, but the 200 rpm fluctuations seem like that to me. Can you use tow/haul mode at the same speed and see how it acts? Maybe go to the next lower gear and observe as well.

I'll try and remember to do some more testing tomorrow, but generally, when I start manipulating things manually like locking the trans in 2nd or 3rd gear I can't replicate it. I have not tried tow haul mode yet, but I know for certain when going up a slight incline I have used tow haul mode so the trans would downshift to prevent this from happening.

Nothing skips or stutters or is rough. Downshifts fine, I don't feel a delay in power, and I sense no slipping either.

 

[RobbyD]

^^^ X2 ^^^

You said any gear any speed, does that include 1st gear? (1st does not engage TCC) Try monitoring your TCC slip rpms.

I very well could've exaggerated that as this has been going on for months now and I'm just now trying to resolve it. I'll edit the OP to not confuse others who might have this issue. I have not tried locking in first gear to try and replicate.

When it happens like I showed in the video: 45ish MPH at 1250-1750 RPM in what seems to be the OD gear going up a slight grade (1-2%).

It happens on flat ground as well but the parameters change a little, but the same thing happens regardless.

Do most scan tools allow for TCC slip monitoring?

 

[mikez71]

What you describe is the easiest time for it to slip. And since it's oscillating gently, it might be sneaking past your seat-of-the-pants dyno..

I believe your scan tool should have TCC slip. If not, you might have to compare input shaft speed and engine rpms or something.

Might be good to dig up the tranmission rebuild receipt if you still have it. Have heard of aftermarket clutches not liking the factory programmed slip amount.
Possibly can get it tuned to help lockup, may want to check your trans fluid.

Once @NickTransmissions sees this, you'll be set! I'm out of my comfort zone, so I'll shut up now before I add confusion!

 

[B-train]

When the torque converter went out on my 2015 3500HD with the 6.0L, it was doing similar things. I went on the test drive with my buddy at the GM dealer and watched while he drove and recorded slippage. Similar with my 2017 6.2L 8 speed trans with the shudder before the fluid was changed.

The speed and rpm you mention definitely seems like TCC to me.....you're right at the sweet spot of lugging it in OD.

 

[donjetman]

sounds like torque converter to me too

 

[RobbyD]

When the torque converter went out on my 2015 3500HD with the 6.0L, it was doing similar things. I went on the test drive with my buddy at the GM dealer and watched while he drove and recorded slippage. Similar with my 2017 6.2L 8 speed trans with the shudder before the fluid was changed.

The speed and rpm you mention definitely seems like TCC to me.....you're right at the sweet spot of lugging it in OD.

sounds like torque converter to me too

In your guys' experience/opinion, does this sound like something that can be suppressed/stopped from getting worse, or is this a torque converter replacement type deal?

 

[RobbyD]

What you describe is the easiest time for it to slip. And since it's oscillating gently, it might be sneaking past your seat-of-the-pants dyno..

I believe your scan tool should have TCC slip. If not, you might have to compare input shaft speed and engine rpms or something.

Might be good to dig up the tranmission rebuild receipt if you still have it. Have heard of aftermarket clutches not liking the factory programmed slip amount.
Possibly can get it tuned to help lockup, may want to check your trans fluid.

Once @NickTransmissions sees this, you'll be set! I'm out of my comfort zone, so I'll shut up now before I add confusion!

You've been very helpful. Thank you for the insight. Here I was thinking it was something stupid like an intake manifold gasket or something off with the TPS.

 

[Geotrash]

In your guys' experience/opinion, does this sound like something that can be suppressed/stopped from getting worse, or is this a torque converter replacement type deal?

Depends on how much wear it's caused on the lockup clutch (assuming that's the problem). My guess is that if it's slipping that badly, the clutch is probably shot. But the clutch may not be the root cause. The root cause may be insufficient pressure in the circuit to keep it locked, which would point to another problem such as a valve body problem or the pump itself being unable to generate sufficient pressure. Who rebuilt your trans, and do you have a list of what they did?

 

[Marky Dissod]

In your guys' experience/opinion, does this sound like something that can be suppressed/stopped from getting worse, or is this a torque converter replacement type deal?

(Geotrash, forgive me for riding along on the coattails of your post ...)
In other words, replacing the TCC alone may not solve your problem.

Who rebuilt your trans, and do you have a list of what they did?

Just as important: WHEN?

 

[RobbyD]

Depends on how much wear it's caused on the lockup clutch (assuming that's the problem). My guess is that if it's slipping that badly, the clutch is probably shot. But the clutch may not be the root cause. The root cause may be insufficient pressure in the circuit to keep it locked, which would point to another problem such as a valve body problem or the pump itself being unable to generate sufficient pressure. Who rebuilt your trans, and do you have a list of what they did?

It was an independent transmission shop here in North Jersey. They're reputable here in the area and I was referred to them by other mechanics/customers. I have to see if I can dig up the RO or maybe I can call them and they'll have one on file. M&O Transmission in Mine Hill, NJ if anyone cares to look them up.

(Geotrash, forgive me for riding along on the coattails of your post ...)
In other words, replacing the TCC alone may not solve your problem.

Just as important: WHEN?

Rebuild was done June 7, 2021 at just under 200,000 miles (198,000 or so if I remember). I'm now at 230,000 and change. I had asked him when I picked the truck up if I would need to do a trans flush after any certain amount of time and he said I would be good for normal factory intervals (i.e. no break-in period).

 

[Marky Dissod]

Rebuild was done June 7, 2021 at just under 200,000 miles (198,000 or so if I remember). I'm now at 230,000 and change.

I'd've ALREADY changed the ATF and ATF filter - I change ATF & coolant every two years.
I say go back to M&O and see what he says ...

 

[RobbyD]

I'd've ALREADY changed the ATF and ATF filter - I change ATF & coolant every two years.
I say go back to M&O and see what he says ...

I'm not really towing with her anymore, so I haven't been as strict with my changes as I once was. And I just hit the 30k mark which is the max I would usually go, but again just commuting now a day 70/30 highway/city.

I'll be giving them a call later today and see what insight they can provide.

 

[Dustin Jackson]

Before jumping to the torque converter being bad lets investigate things that would cause the TC to engage or disengage. Maybe the transmission is being commanded to exit/enter TC lockup?

This looks like a 07 4l60e