howto get rid of rpm hunting / surging on warmup
#1
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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.
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
![Big Grin](https://www.jaguarforums.com/forum/images/smilies/biggrin.gif)
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.
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#3
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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 ,
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 ,
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#4
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Chuck Schexnayder
XJ XJ6 / XJ8 / XJR ( X350 & X358 )
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10-24-2015 10:20 PM
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