4l80e transmission pressure question

[kingtal0n]

I see from various sources that the trans pressure on a gauge in psi pretty much right off idle should be nearly max (for that gear)

The numbers given in psi,
for example
Idle 90psi neutral
Reverse 220psi
drive 1st gear off idle 180psi~

etc


So what is the deal with the shift pressure numbers? Why aren't they all maxes? Why do we put such low numbers in the low regions of the map if the trans always needs high pressure?

[kingtal0n]

I must have watched 50 different videos of 4l60 and 4l80 pressure gauges on vehicles...

and none of them show the transmission pressure while the vehicle is driving / shifting!


I broke down and ordered a $10, 300psi 1/8" NPT sensor for mine so I can log pressure while I drive.

will update when I figure this chit out

[3strokeEngine]

You're getting line pressure and TV pressure confused.

Line pressure is the pressure directly after the pump/regulator valve. Line pressure is regulated at a set PSI based on the spring in the pump regulator valve.

Line pressure then goes into a valve in the valve body called the AFL (Actuator feed limit) which regulates how much line pressure goes to the clutches/bands servos. This valve has two inputs (Line pressure) and TV pressure (Controlled by the PC solenoid on 4l60e and by the throttle valve on the older 700r4s).
The output of this valve is your final shift pressure if you will.

The table we see in hptuners of line pressure vs torque (which is actually directly related to the TPS sensor. 0% being 0 ft lbs and 100% being 640 ft lbs). This is the TV preasure that feeds the AFL valve. 0 psi doesn't mean 0 psi of line pressure it means 0 PSI of TV pressure acting on the AFL valve.

High pressure of 90 PSI forces the AFL valve all the way to the back of the valve body and applies full line pressure to the servos. Now the reason we dont set the whole table to 90 PSI is because the transmission would shift much too hard (think of a manual shifting with out pressing the clutch pedal). However on the contrary too little pressure and with high engine torque the clutches/bands aren't applied hard enough to not slip. Once you start slipping them they're toast in no time and you need a transmission job.

It's a balancing act but rule of thumb is always more TPS% needs more TV pressure.

[kingtal0n]

I'm a little confused how the switching from tps pressure to shift pressure occurs. Like when the commanded pressure is 80% then it's time to shift it might drop to say 30%. Why does the factory seem like its pulling all the pressure out during low torque shifts.

Or better question. It seems like when I increase shift pressure my shifts actually get slower and feel worse. I can't explain that one yet.

[3strokeEngine]

I'm a little confused how the switching from tps pressure to shift pressure occurs. Like when the commanded pressure is 80% then it's time to shift it might drop to say 30%. Why does the factory seem like its pulling all the pressure out during low torque shifts.

Or better question. It seems like when I increase shift pressure my shifts actually get slower and feel worse. I can't explain that one yet.

The factory runs the really low shift pressures because the factory setups the calibrations to lean heavily on the torque management to not burn the clutches in the transmission while keep a smooth shift that will make it out of warranty period. I personally like to turn all torque management off completely and tune my shift pressures to get firm shifts that won't burn clutches but not too firm.

That second question depends on what ECU you're running. If its GEN3 (Vortec BB, 0411, p59, early E40 cals) then the torque values you see at the top of the base upshift pressure table is simply TPS%.

GEN 4/GEN 5 ECMs run the transmission off of the virtual torque tables. So that torque in ft lbs you see at the top of the table is actually a calculated value from a bunch of factors including EQ ratio, timing, airflow, etc. If you have torque management on during the shifts on those ECUs you'll almost always be in the first few cells of that shift pressure table because the ECM is pulling a retarded amount of timing during the shift and that virtual torque signal goes very low and forces you back to the 0 ft lbs area of that table. Hopefully that made some amount of sense...

Post your tune and I'll take a look at it and see what you need to do

[3strokeEngine]

Another thing go into your Force motor current positive and negative tables and make sure the last cell (92 psi/640 kpa) has 0 amps all the way down

[kingtal0n]

It is a 411 Gen3. So the top row is TPS huh...

Well thats weird as hell. Because it does this weird thing, where

if I turn the boost down to 3psi and the car is very slow, accelerates very slow, at WOT (maybe 300hp?) it shifts very lazy and slow and almost like it slips.

But when I turn up the boost say 7+psi of boost at WOT it shifts much firmer and faster.

So thats pretty weird

I dont have the file on this computer will post it after finals

I have some logs which include commanded trans but im afraid polling interval isn't high enough to catch good data
20-02-29 18-07-20.hpl

Apparently is it okay to turn the pressure up to max (89mA or less) after say 50% throttle input then? I See this in many 4l80e files thats been 'retuned'. I've been afraid to use the maximum pressure because I'm worried about blowing out a seal or something. So I use a alot of torque management usually. but lately I've been getting adventurous and turning down the TM and up the pressure. Which is what got me wondering if I should just command 100% of the pressure at WOT and be done. And after experimenting and reviewing logs, nothing makes sense, I realized that I am totally blinded without a gauge so working on that.