Hi,

after reading all threads about that annoying "rpm hunting" many of us experience during warmup, I'd like to share the results of my investigation.

How does the torque converter lock ?
There's a valve no 6 in the gearbox, which drives the clutch for locking.
To avoid vibration from the turbine, it's a "unperfect lock" with a slight slipping achieved by the TCM in regulating that valve.
When the oil gets warmer than 30° (cel), the locking mechanism starts.

What is the problem of hunting ?
My measurements showed the TCM slowly decreasing the pressure on valve no 6 when suddenly the turbine's rpms increased, while the gearbox output rpms remain stable. The TCM recognised that problem and increased the pressure.
Hunting is basically a combination of the TCMs software, the cold oil and probably some wear within the gearbox.

Howto get rid of hunting ?
In a german BMW-forum, I read the same issue of 6HP26 and I read about a sw update of TCM that raises the locking temperature to 40°.
Although my car was serviced by jag dealers for more than 8 years, all software was dated 2002/2003. So I updated my TCM ( which took 30min and showed all possible signs of a bricked car while flashing ) , I cleared the adaptations and I drove that adaption cycle.

Seems like hunting is gone now ... as I did the adaptation cycle allready bevor TCM update, I'm sure, the sw update was the point. My TCM sw is now dated 2005.

 

How did you flash the TCM?

 

I bought a mongoose cable and the SDD-Sw.
As I don't have access to engineeringmode or coded access, I put in some symtomes about gearbox. So I found a menu to update an existing or new TCM.
Afterwards you'll have to clear TCM adaptations and drive the cycle.

My hunting is not 100% gone, but it is so litte, that my passengers don't notice it any more.. but I do.. as I became very very sensitive ,

 

600 dollar cable, and ? for the SDD-Sw, which google wouldn't find for me. I'd like mine gone too, but the price is too high. I like what you've done here though, too bad Jaguar didn't follow through on it.