TCC Surging...

[arubenstein]

As I've been dialing in this transmission (4L70E in a 08 Suburban with a 6.0L), i've come across something I simply can't stop or figure out.

Take a look at the attached log file. The long story short is that when the truck is at the cusp of apply, like about 40 mph in fourth gear at partial throttle, the TCC PWM varies up and down considerably. The net effect is that TPS and VSS are constanct, but TCC PWM is up/down/up/down and the RPMs follow it.

My gut tells me there is more going on here that is being missed. I guess the root question is, what dictates the TCC PWM? I am almost betting there is another table somewhere that defines TCC PWM vs. TPS or VSS or RPM or something.

I know I can set min PWM to 80 or 90, and max to 100; but the application of the TCC is so abrupt that it feels like the driveshaft will fall out (yes, I have a high stall converter).

If my above assumption is true, it's be better if you could define the PWM based upon TPS or something, and still keep your min PWM low. You could then lower TCC apply rate, and have a nice reasonable lockup with minimal abruptness. I don't know about you all, but I'd like to see a lockup that starts at 0% PWM and goes to 100% PWM in one second or less. But, not 0 seconds.

[arubenstein]

Forgot to attach.

[arubenstein]

Anyone?

[joecar]

Does your tune meet this:
D1001 > D1004 (if you lock in 2nd)
D1002 > D1005
D1003 > D1006

The difference should be at least 5 mph (imho).

[99TransAmls16spd]

Old thread, I know... My 06 is doing the same thing - even on the stock tune. It only does it at slow speeds locked in 4th at light loads. My logs look near identical to the one above. At first I thought the PWM bushing may be worn (truck has over 100k miles), but wouldn't that cause the issue at all rpms?

Anyways, I have tuned around the problem by increasing my 3-4 shift and lock up(4th) speeds. I plan on setting D2904 to 100, increasing D2903 by 20 or so, and increasing D2905 by 50%. I would really like to lock the TCC at the factory lower speeds for milage, any thoughts?

[arubenstein]

Old thread, I know... My 06 is doing the same thing - even on the stock tune. It only does it at slow speeds locked in 4th at light loads. My logs look near identical to the one above. At first I thought the PWM bushing may be worn (truck has over 100k miles), but wouldn't that cause the issue at all rpms?

Anyways, I have tuned around the problem by increasing my 3-4 shift and lock up(4th) speeds. I plan on setting D2904 to 100, increasing D2903 by 20 or so, and increasing D2905 by 50%. I would really like to lock the TCC at the factory lower speeds for milage, any thoughts?

Long story short: it should be doing this. What I discovered is that part of the GM strategy on TCC Lock is to allow a very minute amount of slip. This is normal. If you are running a stock TCC, there is nothing to worry about here.

[99TransAmls16spd]

Thank you for the quick response.

The issue with mine is that when it's doing this at the lower rpm, I get a bad "shudder". Its pretty violent, at first I thought maybe it was the "exhaust harmonics", but when I log, the rpms jump around 70rpm or so. When its not shuddering, there is some slip, but not 70 rpm up and down.

[arubenstein]

Maybe there is an actual physical problem with the TC.