How to incorporate altered force motor into tune?

[Rinkrat456]

When I rebuilt my 4L65 I used the common high horsepower transmission rebuilder's trick and turned the screw on the back of the force motor 1/4 of a turn. This is supposed to increase pressure outside of the HPTuners realm.

I noticed my trans was shifting extremely hard upon the maiden first drive, so I changed the normal shift times from a 'sporty' .200sec to that of a factory SUV. I also lowered the Max pressure value down from 99 to 92, as well as softened up the shift pressure under normal driving conditions.

Instead of hunting blindly, does anyone know exactly what tables the force motor trick affects?

[Cantalope Kid]

The force motor current is a relief valve that requires an electrical current to actuate, which will then reduce transmission line pressure. The higher the current the lower the line pressure. Changing the values to lower values will increase the pressure in the transmission system. I've always read its NOT recommended to change the Force Motor Current in the tune as we have access to plenty of other tables to raise pressure. I've even had to turn DOWN several transmission pressure setting once a shift kit is installed. This was in 4L60E setups mind you.

I have NO IDEA where you would adjust force motor current on a 4L65E.

Russ K would be the man to ask in my opinion.

I used to reference his base trans. tunes in the early days to figure out what tuners where REALLY changing.

The WHY came much later...

[262]

First of all do you even know what your max line pressure is now?

Second what other parts did you use? What servos? What band?

You would need to get in and adjust the EPC table itself then massage the line pressure tables. However depending on what servo package you used along with your blind adjustment to the EPC you could have line pressures that are out of control

[jimmyblue]

The screw modifies the mechanical regulator setpoint. The
force motor (PCS) then divides down (blows off) pressure
from there. I'd get a line gauge on there and make sure
the pressure is within spec limits, but to the high end.

The main problem with line pressure is not that the max
(mechanical) is too low, it's that the pressure is rolled
on too leisurely with load (especially if you're one of those
geniuses who lies about airflow trying to get lean). This
is there some tailoring of the force motor makes sense.
Bring the pressure up faster w/ load and all in by 300lb-ft
and you probably won't burn any frictions.

Trans is going to see full pressure at WOT anyway, it's
not like upping the pressure in the midrange is going to
break stuff.

[Rinkrat456]

I figured a little extra pressure could help considering the trans has two large coolers to push fluid through, and the 4L65 was built to withstand off-road abuse and lots of low end torque.

If I put a mechanical gauge into the line, what should the actual pressure at the coolers be?

[01ssreda4]

I got a similar condition, with a stock trans my tuner's trans tables gave a nice crisp shift. When I had the trans built and an HD2 was installed, the 1/2 low speed shift became ground shaking, even through a 4k converter. I lowered the upshift modifier tables on the 1/2 in the low torque range by about 25% and all is well.

[wyochimneysweep]

you would want to check line pressure. theres a port on the side of the tranny thats 1/8 pipe thread and you would hook gauge up there. the pressure out to the coolers isn't the same as line pressure. the fluid that goes out to the cooler just comes back and lubes the tranny. none goes to the clutches or vavle body

[01ssreda4]

theres a port on the side of the tranny thats 1/8 pipe thread

No it isn't. Pipe thread is tapered, the trans has a straight thread.

[Rinkrat456]

Secondly, put a line pressure gauge ($55 shipped on Ebay, or visit a local Transmission shop) on the pressure test port and go for a drive to verify proper line pressure. Base pressure at idle in P,N,OD should be around 70psi and around 140psi in R. Max line pressure should be at least 190psi at WOT in 1st or 2nd, 225psi is optimum. If base pressure is low, Transmission or pump is worn out. If max pressure is low, check Electronic Pressure Control (EPC solenoid. If reverse is slow to engage, and line pressure does not come up to at least 130psi in reverse, replace the boost valve with a Transgo 0.500" boost valve Easy fix by removing the pan.

I found this online. I don't have a pressure gauge but I do have a very helpful transmission shop nearby that I got my parts through, so perhaps I'll just stop by there to have them test the line pressure for me. Probably wont be until Friday though.