crewchef

iTrader: (6)

Posted over on HPT forum too but no response there yet.

Trying to get an understanding of what these are and what they do before I try to do any tuning. Working on a conversion car, 88 TransAm GTA w/ 98 LS1 and 2000 4L60E. Hasn't been up and running long, about 200 miles on it so far. My interest in the Trans tables is based on having to rebuild the 4L60E after loosing 3/4. Of course transmission was bought used and I didn't tear it down before install which in hindsight was probably a mistake. Anyway, on to the the question(s).

Force Motor Current is based on Temp and Commanded Line Pressure. I think the commanded line pressure is based off values listed in the Base Shift Pressure vs. Torque vs. Gear which is the other axis on the Force Motor table is this correct?

If Base Shift Pressure is commanding pressure during shifts, what table is commanding the constant line pressure when you're in a gear. Say I'm in 4th cruising on the interstate, what table sets line pressure to keep enough pressure to stay in gear without clutch slip?

What is the difference between Force Motor Current Positive/Negative. My tables seem to read exactly the same including x/y axis and field entries.

Lastly, my fields in the Force Motor Current table seem to be high as compared to some numbers I read in post on HPT forum. They are at stock settings. Wondering if these high readings (reduced line pressure) would contribute to clutch wear? Reading down the last two columns

90 - 215,215,254,234,215,195,176,156,156,156,156,156,15 6,156,156,137,137
96 - 215,215,254,234,215,195,176,156,156,156,156,156,15 6,156,156,137,137

Any suggestions on tunes appreciated too. It's my son's daily driver, would like moderate shifts for normal day to day with something firmer for wot at the track.

jimmyblue

iTrader: (11)

The force motor is the full time mapping surface that
translates the commanded line (%) to a modulated
line pressure.

The Base Shift Pressure is what's commanded during
shifts (as modified). Unfortunately we do not have any
access to the "normal" line pressure vs load profile.
This is where guys with smaller-clutch torque converters,
and guys making more power than stock, might want a
little help.

Base Shift Pressure controls the speed and the clutch
packs' "authority" during shifts. All you need is to get it
done in an acceptable time. There is a minimum practical
set by the hydraulic / mechanical realities. There is some
chance that adding pressure, beyond this, will in fact
either not help, or muss up some of the phasing between
release and apply actions. You can look at scanner PIDs
like "time of latest shift" to see the cycle time, and quit
bumping up line% once you see no proportionate cycle
time improvement from adding line pressure.

Force motor os your direct handle on line pressure. There
is a sticky up on the HPTuners trans tuning section that
shows a few vehicles' actual line vs force motor current
profiles. If you have a holding-torque problem in gear or
with converter locked, this may be your only tool. But if
you jack up pressure you will have more pump losses and
perhaps accelerated wear, though I have been running a
somewhat modified table for a couple of years now with
no ill effects (yet). Less current at the lower % columns
will make up for the PCM starving line (0%) at low to
moderate loads, including highway cruise & light grades.
Here, all you need is to get the clutches not to slip; more
does nothing. Watch the TCC slip RPM, and input/output
shaft slips (these latter, as ratio, should exactly match
the nominal gearbox ratio; any flare with sudden TPS or
airflow changes, in gear, may indicate you want more line).

Where I started with the force motor table was to make a
synthesis of the 'vette and GTO tables I found, taking the
min() of each cell-wise (this resulting in a maximum line
pressure, yet evidently factory-sane). Then I kept on
upping it until my converter clutch slip became tolerable
(a gimp unit). I wouldn't encourage you to go that far
unless you are chasing a similar problem.

But there's no good reason to be blowing off useful line
pressure at WOT, which is what 200mA of force motor
current is doing.

If you push the force motor table around you will want
to re-re-adjust your shift pressures; some guys who
took my force motor table have noted harsh shifting
down low (esp. when putting it onto a stock converter
car which doesn't soak up the shift-bump as much).

crewchef

iTrader: (6)

Well I've read it twice and I think it's starting to soak in, maybe a few more times and I'll get it. Couple of questions.

Difference between Force Positive/Negative, I think that's the only thing you missed in my first post.

On the force motor table am I correct that the top axis is based on 1) a value for normal line pressure during all states other than the actual shift that we can't see or touch 2) Base Shift Pressure table cell value during shift function?

I have created a view that allows me to monitor engine rpm, input/output rprm, trans temp, PWM %, etc. So far so good with no spikes (rpm) noted so it appears everything is working fine. I do believe a little more line pressure would be a good thing up to a point, especially under light to moderate load as you mentioned in your reply. I can also see firming things up under higher torque too.

Have you got a .bin file on the Horist site that I could download and look at?