I know that PCM uses the MAF to calculate shift speed etc... But what if i tune the MAF, wont that trick the PCM to use wrong shift speed?
I know that PCM uses the MAF to calculate shift speed etc... But what if i tune the MAF, wont that trick the PCM to use wrong shift speed?
Pontiac Trans Am WS.7 Ram Air -98&&
The PCM doesn't use the MAF for any shift points (neither speed nor rpm based, nor WOT nore part throttle). It references the MAF for line pressure. From my experiences it is not enough of a change in the MAF to cause detrimental changes to the trans pressure. If it does, simply readjust the pressure tables.
OK, Thanks.
Pontiac Trans Am WS.7 Ram Air -98&&
The PCM uses torque as the main reference for the trans line pressures. However, the PCM also uses airlfow to calculate torque. So, by drastically changing your MAF curve you are changing the amount of torque the PCM thinks the engine is making. If you make it think less (by lowering the MAF table) then the shifts will soften slightly.
Chris...
I count sheep in hex...
Ported MAF / GMAF guys often report soft shifts,Originally Posted by 12secSS
sometimes damage from wimp applies under load.
If the MAF table makes the modified MAF's frequency
back into realistic airflow data then there's no issue.
You wouldn't want to make the MAF table serve any
other purpose, than true calibration of air mass flow.
I wish, oh, do I wish we could get the line pressure
vs load tables to play with. I believe all the stuff we
have is only for -during- the shift event and I need
to get at the -holding- pressure (like for uphill cruise).
There is quite a bit to the steady state trans pressures, they can also be adaptive (based on slip). The main values are just simple gains and offsets based on gear and if the TCC is locked and there is a temperature compensation as well.
As you can imagine the adaptive routines (if used) are not so simple...
What is your OS# ? I'll see if i can whip something up to test.
Chris...
I count sheep in hex...
Messing with the MAF (for example to adjust LTFT) really changes the trans behavour (line pressure).
I didn't like it because it makes impossible to fine adjust shift pressure.
I changed the MAF curve by max 5% (very low frequencies); more than that I could notice it in the shifts.
Chris: I know you can modify the 98 program to run SD without having problems (disconnecting the MAF causes all shifts to be at max pressure).
How does your program calculates torque for correct shift pressue? VE?
1998 convertible Trans Am
MODS: A4 > M6 conversion, SC raptor hood, Vortech V9 G-Trim SQ, homemade water-alcohol injection
DYNO: 410 RWHP, 417 TORQUE @ 5 PSI
Under a mafless tune, how does the PCM calculate torque to determine the line pressures?
I have a mafless tune, and with stock line pressure settings and shift points my shifts are very firm right through the rev/load range (up and down). Reducing the pressures by 10% across the board has helped, but they are still a lot firmer than standard. ( vehicle is a '99 Holden LS1, mafless tune, diff ratio changed from std 3.07 to 3.7)
Thanks
Did you just unplug the MAF or actually "disable" it. You can leave it plugged in, set the the MAF fail frequency to 0, then turn off the SES light for the MAF codes. Do NOT disable the codes, just turn off the light for them, doing this sends the comp into SD mode and it wont affect your line pressure.
Chris
2009 Silverado Crew Cab 5.3L, stock.
OK this works for SD tuning and for SD driving in general. In this case there will be a frequency to be used for torque calculation.
But it also works if you disconnect the MAF: in this case how does the PCM calculate torque?
Is it using the VE?
1998 convertible Trans Am
MODS: A4 > M6 conversion, SC raptor hood, Vortech V9 G-Trim SQ, homemade water-alcohol injection
DYNO: 410 RWHP, 417 TORQUE @ 5 PSI
I didn't do the tune. I've tried re-connecting the MAF but it makes no difference, so I presume it's been disabled.
Another question
If i change my MAF for the Z06 and put in the right maf-table, are my shifts then correct? ???
Pontiac Trans Am WS.7 Ram Air -98&&
Update: we've reduced the shift pressures progressively by 10%, 10% and then 15% (at total of 31% off the standard tables). The shifts have gotten slightly softer each time, but are still quite noticeable (firm) at low throttle openings. When slowing down at 0% TPS slowly you can feel the car clunk thru the downshift 3-2 then 2-1.
Changing the "shift properties" tables seems to be having a very small impact (especially since it's off stock) - could there be anything mechanical that is keeping the pressures up?
Did you try to show down the shift times a bit? That might help some.
Chris
2009 Silverado Crew Cab 5.3L, stock.
My car was doing the samething. 1-2 shift and 2-3 shifts. Very firm at low torque loads. Here is what I did and now they are butter soft.
Changed shift times to .500 from 0-480
.300 520-640
this is the same for 2-3 shift
changed Base shift pressure vs. tq vs. gear
1-2 shift made "0" from 0-320
"20" 340 and 360 column
"40" 380-420
"60" 440 and 460
"80" 480 column
did the same for 2-3
Both of these were done only in normal. Left the 3-4 shifts alone in both.
This worked extremely well for my car. Hope it helps
Does anybody know how to make the car shift softer into Drive?
When I put the car in reverse it is just like stock. But when I put it into drive it hits pretty hard. ???
99 SS Camaro A4
MTI air lid, 160 stat, msd wires and ngk plugs, SLP LT's with cats and high flow y-pipe, Dynomax bullet muffler with borla cat back behind it, want it quite!
LS1 HOT CAM 218/228 112 LSA
Forgeline RS wheels 17x9.5 front 17x11 rear, Hotchkis struttower brace, LCA, panhard bar, strange 3.73's, 120 sq. ft of v-1 sound deadener
x2.
And on the uphill cruise thing, is there any way to increase the pressure here? I'm in a stock tranny t/a and hills give my tranny the hiccups. If I could bump up that pressure I'm sure it would make things better.
Are your "hiccups" a hard lock/unlock, or
just a soft RPM flare? The two have some
different causes. Lock/unlock points at
misfire under light - moderate load and
maybe wants engine tune massaging to
fix either real misfiring or misfire detect
sensitivity (more likely the former on a
stock-converter vehicle). RPM flare wants
line pressure, either General Pressure or
force motor profile. Though if you haven't
turned off slip learning and set TCC min
duty to 98%, try that first to eliminate
any meddling.
interesting. ya know, it's all stock except shift pressure and it sounds more like the second one. when it kicks the 3-4 shift it slips a little and otherwise it's just when driving around the engine revs and nothing happens as far as acceleration goes. oh and max tcc duty cycle looks like 96%... is it okay to have a min higher than the max or what do i need to do there?
Last edited by richard head; 11-02-2008 at 10:08 PM.
changed the min tcc duty cycle from 10% to 25% and the issue seems completely resolved. ideas? is it safe to leave it like this on a stock, 165k miles converter?
speaking of converters, it's been to a dealership and they suggested a performance issue, such as a clogged cat, might be the cause. should I unbolt those things and beat all the junk out of 'em or maybe just put in a straight pipe? fuel trims are about 8 points lower most of the time on B2 than B1 and that suggests a richer condition over there that a slightly clogged cat might cause. I think I'm gonna pull the first plug from either side tomorrow and see if it looks lean on the B2 side relative to the B1 side. Very little KR at WOT though so maybe I'm runnin her pig rich. it seems unnatural to need to mess with the stock tune on the stock converter.
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