Inconsistent 1-2 shift point
10-22-2006, 08:21 PM
#1
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Inconsistent 1-2 shift point The last two trips I've made to the track have resulted in an inconsistent 1-2 shift point. I have the rev limit set at 6,900 RPM, and even with a commanded shift point of 6,200 - 6,400 RPM it will tag the rev limiter HARD sometimes. It has ALWAYS shifted 1-2 at a higher RPM than commanded, but this problem is now exaggerated with the FM13 cam and desired shift points of 6,700. There is no problem with 2-3. I can't detect an slip, and it runs strong. Best run of the night was a 12.08 @ 112 on a 1.72, with a Vig 2800.
This is a 1998 Z28, with a stock 4L60E and just over 100k miles. I haven't adjusted the shift pressures in the tuning yet. Could this just be a tune problem or is the trans needing some TLC?
This is a 1998 Z28, with a stock 4L60E and just over 100k miles. I haven't adjusted the shift pressures in the tuning yet. Could this just be a tune problem or is the trans needing some TLC?
10-22-2006, 08:33 PM
#2
I would trying to lower your shift points even lower for the 1-2. Is this since the cam install that you are having this problem? It is more than likely effecting your stall which is effecting your shift points. If this doesn't help it might be time for a little TLC.Vince
10-22-2006, 09:12 PM
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Thanks for the reply Vince. The problem has been much worse since installing the cam. With the stocker, I was commanding a 6,000 shift and it consistently shifted before 6,200.
I currently have the shift point at 6,200, and it's shifting between 6,600 - 6,800. It hasn't tagged the limiter on the street yet though with the 6,200 setting.
Last time I was at the track, the 6,400 setting smacked the limiter very hard with the cam.
I currently have the shift point at 6,200, and it's shifting between 6,600 - 6,800. It hasn't tagged the limiter on the street yet though with the 6,200 setting.
Last time I was at the track, the 6,400 setting smacked the limiter very hard with the cam.
10-22-2006, 09:17 PM
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Originally Posted by BlackHawk T/A
Have you messed with shifts by MPH by any chance?
At 6,900 RPM with 26" tall tires and 3.23 gears, according to a log it will carry 1st gear to 49 mph.
Good idea though!
10-23-2006, 08:39 AM
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Correct, both the MPH and RPM values must be exceeded before the shift is commanded. Lowering the MPH a couple of points allows them to be exceeded well before the RPM, which leaves the RPM table as the controlling factor.
Some people actually zero out their MPH table, but I found that it causes my car to shift right past 2nd gear (skips from 1-3).
Some people actually zero out their MPH table, but I found that it causes my car to shift right past 2nd gear (skips from 1-3).
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10-23-2006, 10:49 AM
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1-2 shift times are set as follows, and have been for a very long time now. Thanks for all of the feedback guys! Please keep it coming, I'm really hoping it's a tuning issue.
0.20000 0.20000 0.20000 0.20000 0.15000 0.15000 0.15000 0.10000 0.10000 0.10000 0.10000 0.10000 0.10000 0.10000 0.10000 0.10000 0.10000
0.20000 0.20000 0.20000 0.20000 0.15000 0.15000 0.15000 0.10000 0.10000 0.10000 0.10000 0.10000 0.10000 0.10000 0.10000 0.10000 0.10000
10-23-2006, 11:37 AM
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Those times "should" have driven you to max line
pressure for the higher torque index range.
One thing to look at is, the force motor table has
a pretty strong trans fluid temp slope embedded
in it, as stock. But I am suspicious that it does
not do the right thing, as I observed worsening
TCC slip at overheat conditions. This may be a
source of variability (trans temp). Do you see it
tag the limiter worse, when hot-lapped? Might
play with the force motor table and flatten the
temperature axis, or make it more extreme (might
use Excel to make some variations, break it down
and build it up) and see if something different
there makes for more consistency.
Too, you may not actually be at the top of the
trans delivered torque range and may be still sliding
up toward max torque, max line. In the midrange
you may not be commanding use of full line pressure
(log it and see). If you're not maxed then you are
exposed to torque-based line variation and that
might well change across cam swaps, external
environment and what-all.
The 1-2 is always going to show the finite shift
actuation delays the clearest. You have to lead
it, some. But you can't tune that well until the
shift action becomes consistent in its timing.
pressure for the higher torque index range.
One thing to look at is, the force motor table has
a pretty strong trans fluid temp slope embedded
in it, as stock. But I am suspicious that it does
not do the right thing, as I observed worsening
TCC slip at overheat conditions. This may be a
source of variability (trans temp). Do you see it
tag the limiter worse, when hot-lapped? Might
play with the force motor table and flatten the
temperature axis, or make it more extreme (might
use Excel to make some variations, break it down
and build it up) and see if something different
there makes for more consistency.
Too, you may not actually be at the top of the
trans delivered torque range and may be still sliding
up toward max torque, max line. In the midrange
you may not be commanding use of full line pressure
(log it and see). If you're not maxed then you are
exposed to torque-based line variation and that
might well change across cam swaps, external
environment and what-all.
The 1-2 is always going to show the finite shift
actuation delays the clearest. You have to lead
it, some. But you can't tune that well until the
shift action becomes consistent in its timing.
10-23-2006, 12:18 PM
#11
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Originally Posted by jimmyblue
Those times "should" have driven you to max line
pressure for the higher torque index range.
One thing to look at is, the force motor table has
a pretty strong trans fluid temp slope embedded
in it, as stock. But I am suspicious that it does
not do the right thing, as I observed worsening
TCC slip at overheat conditions. This may be a
source of variability (trans temp). Do you see it
tag the limiter worse, when hot-lapped? Might
play with the force motor table and flatten the
temperature axis, or make it more extreme (might
use Excel to make some variations, break it down
and build it up) and see if something different
there makes for more consistency.
Too, you may not actually be at the top of the
trans delivered torque range and may be still sliding
up toward max torque, max line. In the midrange
you may not be commanding use of full line pressure
(log it and see). If you're not maxed then you are
exposed to torque-based line variation and that
might well change across cam swaps, external
environment and what-all.
The 1-2 is always going to show the finite shift
actuation delays the clearest. You have to lead
it, some. But you can't tune that well until the
shift action becomes consistent in its timing.
pressure for the higher torque index range.
One thing to look at is, the force motor table has
a pretty strong trans fluid temp slope embedded
in it, as stock. But I am suspicious that it does
not do the right thing, as I observed worsening
TCC slip at overheat conditions. This may be a
source of variability (trans temp). Do you see it
tag the limiter worse, when hot-lapped? Might
play with the force motor table and flatten the
temperature axis, or make it more extreme (might
use Excel to make some variations, break it down
and build it up) and see if something different
there makes for more consistency.
Too, you may not actually be at the top of the
trans delivered torque range and may be still sliding
up toward max torque, max line. In the midrange
you may not be commanding use of full line pressure
(log it and see). If you're not maxed then you are
exposed to torque-based line variation and that
might well change across cam swaps, external
environment and what-all.
The 1-2 is always going to show the finite shift
actuation delays the clearest. You have to lead
it, some. But you can't tune that well until the
shift action becomes consistent in its timing.
10-24-2006, 08:43 PM
#12
If you spin off the line you will over shoot the 1-2 shift most everytime. If you are spinning various amounts each time you will over shoot different amounts also.
Make sure the fluid is in good shape and full.
Log the runs if possible. That will help figure out where the problem is. It is common to over shoot some, but not quite that much.
Make sure the fluid is in good shape and full.
Log the runs if possible. That will help figure out where the problem is. It is common to over shoot some, but not quite that much.
10-25-2006, 08:07 AM
#13
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Originally Posted by TXCAMSS
If you spin off the line you will over shoot the 1-2 shift most everytime. If you are spinning various amounts each time you will over shoot different amounts also.
Make sure the fluid is in good shape and full.
Log the runs if possible. That will help figure out where the problem is. It is common to over shoot some, but not quite that much.
Thanks for the input!
