4t65 force motor current vs psi vs temp question

[mg01074]

Hi guys
I'm working on a 05 Bonneville sle 3.8 na 4t65e. I'm wanting to up the line pressure in the trans and i think this is the right table but the psi in the table doesn't make sense. With a mechanical gauge on the trans main line pressure is way over these psi numbers, over 200 depending on current. Any help would be great..Thanks

Attachment 10125

[Montecarlodrag]

That table is for the apply pressure not the main line pressure. You need to hook the gauge to the correct place.
If the transmission has not been modified there's no need to modify this table.
The less current the higher pressure, normally the PCM will not command higher than 96 psi, if you want more modify this table and it will rise (the transmission has no pressure transducer, all its values are based on this table)

[mg01074]

so is there a table for main pressure to adjust

[lionelhutz]

That table is not psi.

It works basically like this. There will be main "pressure" tables which uses %TPS vs speed. This is called a pressure table, but the numbers in this table are not pressure but rather just a factor. Then, there are other tables that further modify this factor based on other stuff like gear, temperature etc. They all work together add up to a final factor. Finally, the PCM looks up the final factor in the table you posted and gets the current for the force motor. By default, GM uses 96 as the highest factor that can be reached.

So, I would first tune the main pressure tables to try and firm the shifts. Possibly pick some of the other tables and work on them too. You do need to lower the shift times, try 1/2 the original value to start. Only change that force motor table if you need a higher maximum line pressure.

Do not change the "max line pressure" if there is a single factor called that and already set to 96.

The transmission has no pressure sensor and with no feedback there is no way to have a psi vs XX table where you can just enter the psi you want.

[mg01074]

ok thanks i think.. I really dont see any more tables related to "pressure"?? I was thinking that those numbers were just factors since at around 1000ma the pressure is around 60 or 70 not 0

[Montecarlodrag]

Values on that table are milliamps, it's the current applied to the pressure servo which regulates the pressure. The more current applied to it the more it opens and the pressure is lower. The less current the more it closes, until it is completely closed and the pressure will go up to full pump pressure.
When the PCM wants to apply for example 96 psi of pressure it looks at that table to know how much current it needs to send to the servo to achieve 96 psi. The PCM will not know if the pressure is higher or lower. That's why you should not mess with that table unless you can calibrate it using a gauge (for modified trans)

[lionelhutz]

You should have a whole bunch of line pressure tables. There should be a main table and a bunch of modifier tables. I don't have a bin for you car to open in HP Tuners. The LT1 has 14 pressure tables as an example and all of them add-up to the value used to find the current in the force motor table.

When the PCM wants to apply for example 96 psi of pressure it looks at that table to know how much current it needs to send to the servo to achieve 96 psi.

So where do you measure this pressure? I can only find references to using the line pressure port.

Everything I have read says the table goes from 0 to 96 "psi" with 0 representing minimum line pressure and 96 representing maximum line pressure. The current adjusts the line pressure from between say 95psi to 210psi for example.

[RobertISaar]

Everything I have read says the table goes from 0 to 96 "psi" with 0 representing minimum line pressure and 96 representing maximum line pressure.

this is what I've been assuming for years since the table values never really matched anything real-world.

[Montecarlodrag]

So where do you measure this pressure? I can only find references to using the line pressure port.

Everything I have read says the table goes from 0 to 96 "psi" with 0 representing minimum line pressure and 96 representing maximum line pressure. The current adjusts the line pressure from between say 95psi to 210psi for example.

I really don't know how the line pressures correlate to 0-96 psi pressures from the tune.
This is the procedure to check trans pressure. If that check then the table is accurate.

[lionelhutz]

this is what I've been assuming for years since the table values never really matched anything real-world.

Yes. Somehow these factors being called psi have propagated to tuning software all over. Even HPTuner still uses psi for the force motor columns on 2010+ vehicles.

There is much confusion about the settings. There is a maximum scalar that is typically 96 and you can find instructions to raise this scalar to increase the pressure and get a better shift in many places.