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.

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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!