Trans Slip RPM Channel Opinions/Thoughts

[radz28]

Good day,

Can anyone comment on the kind of weight you'd give to this channel in the Scanner? Is this channel accurate, or worth giving much consideration to?

I've been watching this channel, while farting around on my VVE and VTT tables. I have my VVE table to 5-10% correction, and my MAF/VVE/Dyn_AF within a handful of % to each other, but was seeing up to around 100-RPM of slip on that Trans Slip RPM channel. Is that anything to worry about? Sometimes it will go down to about 0-RPM, but I can't see to get it to be consistent.

I've tried raising my VVE slightly higher, and from slightly higher VTT to like 200-lb.ft. higher than it should be, but I can't get it to be very consistent. I started by seeing up to about 1000-RPM slip (when I lowered the VTT to something closer to what the car should be making, at the crank), but increased it since, to have it less than 100-RPM now.

Am I chasing my tail about this? Can anyone comment on what they've observed? I'm welcome to any comments or thoughts.

Thank you very much for your time,
Chuck

[hjtrbo]

Post up a log that shows the slip you're talking about.

[radz28]

Hopefully I did this right...

As the RPMs climb, the slip starts to increase in Step37 v3. However - from the same scan, Step37 v3 2 shows nearly no slip...

I just captured another scan, where TQ was about 200-lb.ft. higher than what this VTT was, and I'm still getting about the same kind of slip, even with line pressure around 160-psi.

Is this kind of thing normal? Sometimes there's almost no slip at WOT. I thought because it was so hot here, that I was running in such a lower part of my spark table (about 12-15* at WOT, total timing) because of my IAT retard corrections, that I wasn't registering enough TQ for the TCM to command high enough line pressure, but even with max pressure (about 160-psi), I was still seeing about 100-RPMs or so.

Is this considered negligible or nothing to worry about?

Thank you, again, for taking time to look and comment.

[hjtrbo]

I see what you mean. I'm picking the gear ratio calc is not spot on. The logs look ok.

If you wanted to be sure you could log input and output shaft speeds (if available) and add in your gear ratio to make your own slip PID.
Input_Shaft_RPM / Output_Shaft_RPM x Current_Gear_Ratio

[radz28]

OK. Thanks SO MUCH for taking time to help. I'll try that out! I've logged the input and output shaft speeds in the past, but didn't know how to normalize them, like you just stated. Thank you SO MUCH​ for that!!!

[hjtrbo]

Good. If you didn't already know you can right click the channels and increase the polling rate. For input and output shaft speeds I would have those logging pretty fast, at least 20Hz.

[radz28]

I knew about that, but hadn't thought to change it, so Thank You for reminding me. I usually run those kinds of polls as fast as I can, but I hadn't remembered to.

FWIW - I precisely matched the ECM gear ratio to the TCM ratio in the TCM. If I calculated it correctly, it seems the like tiny error calculates to up to about the slip I was seeing in the gears that had a slightly differing ratio delta. If that's all I was seeing, then I'm not as worried. Most of my logs seem to show the biggest slip were in the same gear, at the top of the gear, where I'd think it would show the greatest delta, so I believe you were onto something.

Thank you for your continued comments.

CHEERS!!!

[radz28]

I knew about that, but hadn't thought to change it, so Thank You for reminding me. I usually run those kinds of polls as fast as I can, but I hadn't remembered to.

FWIW - I precisely matched the ECM gear ratio to the TCM ratio in the TCM. If I calculated it correctly, it seems the like tiny error calculates to up to about the slip I was seeing in the gears that had a slightly differing ratio delta. If that's all I was seeing, then I'm not as worried. Most of my logs seem to show the biggest slip were in the same gear, at the top of the gear, where I'd think it would show the greatest delta, so I believe you were onto something.

Thank you for your continued comments.

CHEERS!!!

[1scls1z]

100 rpm of slip sounds normal to me. If it was something like 2000 rpm then my guess would be either the converter is not locking or the VTT needs some torque added at higher rpm.

[radz28]

I'm seeing good locking in the TCC. There's pretty much zero slip, which is why I've been concerned. I'd added a sh1t tonne of VTT at higher RPMs but would still get around 100-RPMs of slip.

After trying the ratio calculations from above, I haven't driven the car again yet, but fingers crossed.

Thank you for your comments and thoughts. I welcome them all.

[TheMechanic]

Some of the later model GM trans strategy calls on a soft engagement of the TCC. That's why GM can't keep parts in stock. If you see some slip as in 20 to 30 with full lock up I wouldn't worry to much. The big issue is if you get a slip from 0 to 100-150 then back to zero. Like a sine wave. That means trans time. Diag'd several over the last couple years. Pull the pan and filled with sh*t. Personally I shoot for a lockup that is zero slip

[radz28]

OK. I think I got that. I'm not seeing really any slip with TCC, and not the 0 to 100-15 then 0 as you described. I'll keep an eye out though.

Thank you for your comments.

[lsxjunkie]

im seeing 1500rpm in the Trans slip PID on my CTSV what is VTT pressure? Attached log and file.

[radz28]

Virtual Torque.

As it turned out, after one of the TCM flashes, somehow the ratio value changed. This was just enough that I was seeing some slip. After changing the gear ratio back, the slip values were like before - pretty much nothing.

Much smarter people would have to help you with your issue. If I could, I would. I've seen a couple of them state that VTT tables control shifting (both AIRMASS and MAP tables). What I was trying to do is see if increasing VTT in the areas I was seeing slip would change anything. It didn't help, because the re-flash changed the gear ratio I was seeing the slip in. I don't know if this is the same issue you're having.

[Alvin]

im seeing 1500rpm in the Trans slip PID on my CTSV what is VTT pressure? Attached log and file.

This is because its calculating slip for the gear its going to. Look at current gear. it shows the next gear as the shift is initiated. Normal because the shift hasn't completed yet.