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Vag-Com Log of Trans Hunting! Flog this horse!

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Vag-Com Log of Trans Hunting! Flog this horse!

Old 01-09-2007, 06:31 AM
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Default Vag-Com Log of Trans Hunting! Flog this horse!

Well, With the help of the Vag-Com logging function, (Display groups 7 and 8) It is plain to see that the tranny on my vehicle only slips at the TCC when the pressure is modulated.
Lock up at .744 amps current always results in zero slip! That's good! The TCC is still up to the task of power transmission.

The TCC solenoid Valve 4 (N218) is displayed open at .144A , But in the PWM .4 to .55 amp display range, the hunting is seen as rapid variations in Trans-in vs Trans-out values (Group 7 zone 4,slip speed). These transients appear to only occur at the solenoid PWM power values of .4-.55 amps) without apparent attempts by the TCM to make any correction by increasing or decreasing the duty cycle. This would be the "controlled slip",function but it seems to be out of control. Response time? These events often take less than 1.5 seconds.

A second drive cycle log of transmission functions, Display groups 2,5 and 6, does not give evidence of any strange shifting patterns between any gear changes, even though hunting was evident during the drive cycle.

With this information it appears that both the transmission and the valve body are doing what they are instructed to do.

The behavior of the TCC is erratic when in controlled slip, PWM control. Perhaps this is due to worn friction material on the TCC and interaction with the Transmission fluid.
Perhaps it is that the command signal is generated inappropriately. I can not think of a reason to interject a partial unlock of the TCC under the driving conditions during these tests.

There does not appear to be a correction from the TCM to counter the slip variation. applied current values remain much the same until either release or lock up current values are seen.

The relationship between the throttle position factor and slip speed is inconclusive. There was but one instance of a rapid change in TPI associated with erratic slip fluctuations. The other episodes of slip are correlated to constant or linear TPI value changes.


Nothing yet.....
it seems that a few more test functions need to be discovered.

Perhaps others can see were I can not.

CalG is offline  
Old 01-09-2007, 07:05 AM
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Default I think you are on the right path

I am still thinking it's an input to the TCU that is causing the hunting......please figure it out!

The only thing I haven't changed is the throttle position indicator.
PaulW is offline  
Old 01-09-2007, 07:42 AM
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Default Workaround?

Since the problem is almost certainly TCC lockup related, can we 'hide' the TCC lockup signal until certain parameters are met?

For example, route the input of TCC lockup signal thru a relay takes a secondary input (say, speed sensor >65mph).
On my previous car, the TC would only lockup at higher speeds (over 80kph); you'd sacrifice some fuel economy, but really who cares?
Above 65mph, there seems to be enough line pressure to keep the tranny from hunting.
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Old 01-09-2007, 07:56 AM
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Default Re: Workaround?

The data log shows that when the lock up signal is given, indicated by a applied amperage > .7 amps. The TCC does not slip.
There is enough pressure at all engine speeds.

The condition that may be a problem is if the applied PWM power has insufficient response to deal with real time fluctuations of stick slip.

This points to a fluid/ friction materials issue.

More as it developes!

CalG is offline  
Old 01-09-2007, 08:40 AM
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Default Kudos and please continue.

I have always felt that this tranny had its issues in the tcu. I suspect the TPI and even the brake switch-- or the stupid location of the TCU in a high humidity environment (gee those drains are really great when they plug up with one little leaf and flood the TCU and then the cabin floor).
audilvr is offline  
Old 01-09-2007, 08:59 AM
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Default check against a known good tranny

or post your test routine, and get others to copy it to compare against...
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Old 01-09-2007, 09:17 AM
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Default Re: check against a known good tranny

I will gladly share the data (excel file) but need instruction on making attachments available. I do not maintain any site to upload to.

Correlation with a known good trans would be helpful.


CalG is offline  
Old 01-09-2007, 09:28 AM
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Default Whoa! Some distraction on TCC

Nicely done sales Tech By Sonnax

Not our Transmission, but the info applies.

What to look for in a VB rebuild

CalG<ul><li><a href="http://www.transmissionspecialty.com/TB/tb-volume3-4.pdf">http://www.transmissionspecialty.com/TB/tb-volume3-4.pdf</a</li></ul>
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Old 01-09-2007, 09:31 AM
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Remember there is a retard signal sent to the engine to smooth change
Always Overcharged is offline  
Old 01-09-2007, 09:33 AM
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Default there must be some way to trick the TCU into thinking the trans is cold all the time

then this behavior wouldnt occur bc it wouldnt lock the tc at low rpms...

(I do recall that this behavior does not occur with the engine / trans cold, right?)
Angus Beef is offline  

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