I came across some interesting "news" in a technical service bulletin. It concerns a change in the force motor (pressure control solenoid) back at the beginning of the 1994 model year. Is shows that the old force motor "operates at 292.5 hz level" and the new force motor "operates at 614 hz level". Anything I read about controlling the transmission hydraulic pressure says that you need to vary the current to this motor from .1 to 1.1 amps. The voltage is the battery voltage. No where have I found anything that the voltage/current to this motor needs to be at a certain frequency. Can someone explain what this all means? I am piddling around with making my own transmission controller and this may be information that I need.

Also when in reverse the pressure goes up over 300 psi. The max pressure that can be commanded by the pressure control solenoid is around 170 psi. I suppose there is another circuit causing the high pressure. Should the pressure control solenoid be set to high pressure, low pressure, or does it even matter when in reverse?

thanks

91-93 used one force motor and then 94+ used another one. They changed the frequency tha the solonoid worked at so they could eliminate the cleaning cycle that the earlier 91-93 solonoid required. The force motor is a pulse width modulated solonoid which means that it does not use a direct current, but a modulated one. A pulse width modulated current is also refferred to as a frequency. The 2 solonoids do not interchange, but GM does make an updated PROM chip to allow the use of a 94+ PWM style into the 91-93 trucks. The 4L80E also uses a reverse boost valve like the 4L60E does which roughly doubles the line pressure in reverse to increase the holding power since so many clutches are activated to get reverse. My book lists the line pressures to range from 35-171 in D, P, or N, and 67-324 in R. Also if you unhook the force motor it will go to max line pressure as the force motor raises line pressure with less current.

pulse width modulation and frequency are different. frequency gives the rate at which the pulses are sent and pulse width modulation is the percent of the time that the pulse is on (duty cycle).

The TCC is pulse width modulated. It is controlled by the duty cycle. It is my understanding that anything less than a 20% duty cycle the torque converter is unlocked and anything over 80% duty cycle the torque converter is locked up. I guess the torque converter resistance varies with duty cycle between 20% and 80% - but I don't know that for sure.

I wonder if the pressure control solenoid is just expects 50% duty cycle. I don't really know why they call it a force motor anyway. I took one apart and it is just a spring loaded pressure regulator. The spring is set in a steel plunger inside a coil. When the supply current is up it has a greater magnetic force and it pulls the plunger back decreasing the pressure. When the current is low the spring presses on the diaphragm harder causing the pressure to go up.

The pressure control solenoid is a variable width. A close cousin of the pulse width solenoid. The difference is the type of control being a variable width one.
The automotive industry has been leaning away from using frequency width. Too many problems.
Variable width solenoids like the pressure solenoid is controlled by amperage. Here is an amp feed chart for the 4L80-E in relation to line pressure.

http://i120.photobucket.com/albums/o187/USMILRET/4L80E%20Transmission/amprating.jpg