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Discussion Starter #1
I usually don't take my wagon over ~100mph, but lately I've done a few high-speed pulls. First gear and second gear upshift just shy of 6000rpm, but third gear doesn't upshift--at least it didn't by 6500rpm, and that's where I backed off out of consideration for the motor. I've been able to get up to 145mph indicated by pedaling it--keeping the throttle light enough where it won't downshift to third--and it still had more left, but at part throttle, it was slow going at that speed.

Is this something that can be edited out in the tune? I assume so but figured I'd ask.

(Engine has upgraded valvetrain, etc, and spins to at least 6K no problem, and rear end has 4.10s. So no, I'm not doing 170mph at the top of third gear--it's more like 115mph.)
 

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In a stock tune 3>4seems to be blocked after 37.5% TPS. This probably is linked to the axle ratio vs HP/Torque of the engine.



I am not a expert. In my home made tune tune for the 3.73 I set it so it would up shift at the maximum speed that linked to the maximum RPM I wanted. This was in the Normal Mode tables. Manual and Cruise modes should be adjusted.



I also changed the Kickdown Mode Up/down tables.


All this should have been adjusted when you put in the 4.10s.



My car came with a Hypertech tune and the car would just shut down the motor without up shifting at WOT. Scary thing in the middle of a single lane highway pass.


The TCC tables should probably be adjusted as well. I do not know enough to recommend what is best. Stock it is blocked at 43.8% TPS.
 

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That's a 2.56 table (sedan, wagon, whatever, doesn't matter), but the 2.93 table treats 3up4 & 4dn3 pretty much the same for both 2.56 & 2.93.

If my memory of the kickdowns is correct, both 2.56 & 2.93 would reach either 108MpH, or whatever the wind allows (about 140MpH) in 3rd.

WX3s, WX8s, and 9C1-LT1s with 3.08 would reach about 130MpH in 3rd if allowed, but for some strange reason, GM programmed the 3up4 to occur before that.
9C1-LT1s (with 235/70R15 ONLY) were programmed to top out @ ~149MpH, and WX3s & WX8s were programmed to top out @ 154MpH, to protect the driveshaft.]

KW Baraka's right, though; prepare for a rebuild.
 

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Not that it matters, that is a screen shot of the original late 94 production calibration out of my 1995 2.93 wagon.
I am not saying it does it or doesn't but what about the fact it is not programmed to 3-4 WOT shift tell you it needs rebuilding?
 

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Not that it matters, that is a screen shot of the original late 94 production calibration out of my 1995 2.93 wagon.
I am not saying it does it or doesn't but what about the fact it is not programmed to 3-4 WOT upshift tell you it needs rebuilding?
I regret being less than clear.

An OEM 2.56 or 2.93 program would not 3up4 @ WOT unless it somehow ignored the 108MpH speed limiter anyway.
Barring that, the 3up4 was originally programmed to occur @ 4000RpM, either 113MpH (2.93) or 129MpH (2.56).

Since TheFleshRocket's pcm was reprogrammed (4.10 with 29" tall tires), it should have 3up4 shifted by 126MpH.
IF not, I'd be engarde for the escalating possibility of a rebuild.
I guess the other possibility would be to recheck the program?
 

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When he talked about an indicated 145 at part throttle, i read that as the calibration hasnt' even been set for the gears.

The 255, as you know, is the top of the math , same as never.

If that was not fixed, even after scaling for 4.1 it would still be 186is

It has been so long since i have done lt1 stuff.
What i remember doing was trying to match the 100% throttle mph tables to the wot shift rpm thresholds .
That so the rpm and mph shifts agree

I also found you had to initiate at least a couple hundred lower no matter how good the trans was.

Fact remains, whoever, if anyone ,touched his cal,needs to revisit .

What i will concede 4th is not robust.
But even if he just fixed the downshift numbers, at least he could hold wot 4th after lifting for the shift
 

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Stock tire 27" 4.10 gear.
29" 4.10

I'm not doing 170mph at the top of third gear--it's more like 115mph.
6000RPM third 118MPH 5590RPM(29")


I've been able to get up to 145mph indicated by pedaling it--keeping the throttle light enough where it won't downshift to third-
5200RPM Overdrive 145MPH 4840RPM(29" Stock peak HP#)


Looks OK for 4.1 gears by the math. I thought stock max speed was lower due to wind resistance vs HP.



I also found you had to initiate at least a couple hundred lower no matter how good the trans was.
I learned this the hard way(RPM engine cutoff mid shift very bad jerk then the engine comes back jerk again).


What i remember doing was trying to match the 100% throttle mph tables to the wot shift rpm thresholds .
That so the rpm and mph shifts agree
Learned this from the forum, PCM shifts by MPH. I used a online calculator(like today's #) to pick my shift points in RPM them programed them by MPH
 

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+1 on 4th gear not being robust. It's not designed for a lot of power, just a low torque, low rpm cruising. But you can upgrade that pretty easy; Sonnax and others sell enlarged 4th gear pistons, and if you're willing to remove the trans and take the pump out, you can easily swap to a wider 2-4 band for more holding power on both the 1-2 and 3-4 shift. Do be aware that if you swap 2-4 bands you should really closely inspect the reverse input drum with a straight edge - it tends to wear in the middle and putting a new band on a worn drum is a recipe for a "thereagain". And if you're in there, you should replace the sunshell with a Sonnax Smartshell and replace the 3-4 clutchpack along with the Sonnax 74140-01k Heavy Duty 3-4 clutchplate backing kit. But anyway...

Yes fix the tune first. And never go into the transmission before verifying that the PCM is actually telling it to do something, using any of the scan tools or dataloggers out there. Check out TunerPro and eehack, and there's very cheap ways to make a USB programming cable.
 

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Discussion Starter #11
I think the tune was originally done by PCM4Less for the previous owner. More recently, I've been relying on Ryan from Sinister Performance, LLC. for other modifications. (I had him adjust the fan speeds for a stock thermostat--the car had a 160, which was too cold IMO, and the fans set accordingly--and disabling the throttle cut on decel as the RPM would dip too low and then recover repeatedly.) I've emailed him (and linked this thread to him).
 

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Discussion Starter #13 (Edited)
I found the part of the tune that looks like it controls shift points. Thing is, I am apparently not doing it properly.

Here is a screenshot from what I think was a stock Impala SS PCM.



Here’s how mine is set right now, and it still won’t upshift at WOT in third. I’m assuming that Normal is the shift map that my car is using.



I’m going to post an acceleration run video here. Started partway through first gear, and running up to more than 6K in third without it upshifting. It looks like 1-2 happens at 30mph and 2-3 at 66mph, both at about 5800rpm. I let off at 5800 in third as it should have shifted before then given my settings.

 

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Not familiar with your program.
In TC you would be looking for Kickdown Mode shift RPM Thresholds

Somewhere you will have hot ,cold, normal upshift RPM threshholds.

They are where the WOT shift should initiate
That is to say, they will have to be a couple few RPM lower than where you want the rpm to go on the shift.

There has been back and forth about what overrides what.

I found my stuff much less confusing to start with if I made all the mode tables the same to start.

Set the RPM shift tables where I want them ( minus a couple )

Then do the math to figure the mph and use those numbers at 100%
 

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Discussion Starter #15 (Edited)
Thanks to 95wagon, I found these settings. The first and second gear shift points look spot on, so I bet if I adjust 122 down to 105, it’ll shift where I want it to. Will hopefully try it tomorrow. Also thanks to Marky Dissod for a very helpful private message.

 

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Make sure to also look at the rpm related tables
You also have the Normal MPH 2-3 shift point set at 80mph at 100% TPS,
which is not correct. It should be aroun 65mph with 4.10 gears.

Since you don't really know what you are doing, I'd suggest getting a new tune from
a professional tuner. PCMforLess and PCMperformance still do tunes for LT1s

Nab
 

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Discussion Starter #18
Hey guys, I’ve got it fixed as of late last week. Upshifts from 3-4 happen at ~6000. I’m going to tweak it a little bit so it shifts at 5800, like it does in first and second. I’ll share my settings the next time I fire up my old laptop to get some screen shots. I’ll follow up on other posts at the same time. Thanks to everyone for your input!
 

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I found the part of the tune that looks like it controls shift points. Thing is, I am apparently not doing it properly.

Here’s how mine is set right now, and it still won’t upshift at WOT in 3rd. I’m assuming that Normal is the shift map that my car is using.
(Clever or lucky bastards have access to the Performance Mode Up/DownShift Points Table. Why we haven't clamored for a B-car Performance Mode harness is beyond my reckoning …)
Manual Mode only applies when the shifter is in 2nd or 1st - when the shifter is in 'D', it uses Normal Mode, locks out 4th/'OD', and applies 3rd's overrun clutches during decels and coastdowns.
Thanks to 95wagon, I found these settings. The 1st and 2nd gear shift points look spot on, so I bet if I adjust 122MpH down to 105MpH, it’ll shift where I want it to. Will hopefully try it tomorrow.
Also thanks to Marky Dissod for a very helpful private message.
Use these calculators to check your numbers:
Tire calculator
MpH calculator

If both KickDown Mode Thresholds > 99%, only the Normal Mode Up/DownShift Points Table gets used, and MpH always determines when shifts initiate.
If both KickDown Mode Thresholds < 99% AND the KDM Enable Threshold > the KDM DisAble Threshold, then while TPS% > the KDM Enable constant, KickDown Mode is in effect.
When KickDown Mode is in effect, BOTH the MpH & the RpM thresholds must be crossed before an UpShift starts.
From experience, KickDown Mode thresholds should be set so RpMs determine when Upshifts initiate.

You're welcome.
Hey guys, I’ve got it fixed as of late last week. Upshifts from 3-4 happen at ~6000. I’m going to tweak it a little bit so it shifts at 5800, like it does in first and second.
I’ll share my settings the next time I fire up my old laptop to get some screen shots. I’ll follow up on other posts at the same time. Thanks to everyone for your input!
Forgot to mention:
When a shift initiates is not the same as when that shift can be said to have occurred.
 
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