Simple question regarding PWM
01-21-2008, 11:35 AM
#1
Simple question regarding PWM Real simple: I'm being told 2 things about PWM, which is right? In case it matters, this is a 1998 Z28.
1) PWM applies ONLY as the TC is locking or unlocking, once it's locked it should stay locked until commanded to unlock (not slip at all during normal driving in the locked range).
2) PWM allows some normal controlled slip of the converter clutch when locked when you hit the gas going up hill (not enough to release the TCC lock), and this is normal unless tuned out.
My 98 Camaro with it's stock converter never slipped climbing hills when stock, now it just recently started slight slipping (RPM's edge up and down slightly) with my Vig 3600. (Vig didn't appear to slip prior to today..?)
1) PWM applies ONLY as the TC is locking or unlocking, once it's locked it should stay locked until commanded to unlock (not slip at all during normal driving in the locked range).
2) PWM allows some normal controlled slip of the converter clutch when locked when you hit the gas going up hill (not enough to release the TCC lock), and this is normal unless tuned out.
My 98 Camaro with it's stock converter never slipped climbing hills when stock, now it just recently started slight slipping (RPM's edge up and down slightly) with my Vig 3600. (Vig didn't appear to slip prior to today..?)
01-21-2008, 11:44 AM
#2
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PWM is setting yout available TCC pressure as a fraction
of main (force motor controlled) line. This is one problem
for small diameter clutches, the stock tune starves the
line at low "delivered trans torque" values (like cruise and
up to maybe 25% TPS). So first sign will be slip on overpass
ramps and the like. Even 100% of minimum, ain't much.
There is adaptive pressure learning that tries to hold a
bare minimum of slip, I guess GM wanted CAFE mileage so
bad they were willing to play the pump drag off against
clutch wear. Thanks. Really. But slip varies with fluid
temp -> viscosity and so on; so does real motor torque
vs modeled motor torque, and converter multiplication
of that torque (which GM knows nuthin' from nuthin' if
you went aftermarket). And you have to bet that a
smaller diameter converter wants more than stock
pressure anyway, for the same breakaway torque or
pull-in torque. Anyway, if the computer learned to
barely slip one day there's a good chance that the
other side of the warm front will make it all wrong
until it wises up.
I've spent many many hours messing with the trans
settings for converters I've had and expect you'll
be needing to, in the end.
of main (force motor controlled) line. This is one problem
for small diameter clutches, the stock tune starves the
line at low "delivered trans torque" values (like cruise and
up to maybe 25% TPS). So first sign will be slip on overpass
ramps and the like. Even 100% of minimum, ain't much.
There is adaptive pressure learning that tries to hold a
bare minimum of slip, I guess GM wanted CAFE mileage so
bad they were willing to play the pump drag off against
clutch wear. Thanks. Really. But slip varies with fluid
temp -> viscosity and so on; so does real motor torque
vs modeled motor torque, and converter multiplication
of that torque (which GM knows nuthin' from nuthin' if
you went aftermarket). And you have to bet that a
smaller diameter converter wants more than stock
pressure anyway, for the same breakaway torque or
pull-in torque. Anyway, if the computer learned to
barely slip one day there's a good chance that the
other side of the warm front will make it all wrong
until it wises up.
I've spent many many hours messing with the trans
settings for converters I've had and expect you'll
be needing to, in the end.
01-21-2008, 12:07 PM
#3
Nice info, I think I am putting this together now. As I understand it, this slipping is not normal or "by design" and I need to make every effort to stop it. So, tuning out PWM will at least stop the car from reducing the available TCC pressure as a "fraction of main" like you describe. This "may or may not" stop the slipping depending on if even 100% pressure is enough with the smaller diameter clutches in the new TC.
Can't I safely assume that the Vig 3600 locking clutch is designed well enough to guarantee lock if I give it 100%?
In other words, if there's slip after the tuning out of PWM, does this guarantee the TC clutch is defective? (barring any problems in the tranny or solonoid.) Or, is it just "known" that this is a side effect of having smaller diameter TC? (I would certainly hope not).
Can't I safely assume that the Vig 3600 locking clutch is designed well enough to guarantee lock if I give it 100%?
In other words, if there's slip after the tuning out of PWM, does this guarantee the TC clutch is defective? (barring any problems in the tranny or solonoid.) Or, is it just "known" that this is a side effect of having smaller diameter TC? (I would certainly hope not).
01-21-2008, 02:05 PM
#4
In our units to avoid this we disable the converter regulator valve. This is the valve thats pulsed by the PWM solenoid to cause the lower line converter apply and resulting slip. Some have different veiws and limit it to near non exsistance which is done in the transgo HD2 kit, This is fine to. The downside is that enable happens long before the 100% apply the lockup may appear to happen early . But this can easily be altered in tuning bearing in mind that the converter now is a simple full presure on and off . Personally I think PWM was a bad idea. I first saw it in chrysler 604 units , There were many issues with converter clutch failure. Later they re did the programng to limit it and there were even some software flashes that eliminated it completely the cars and vans felt much better, Though it did require explaining to the customer what the slight bump in and out of throttle was.
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