Third gear doesn't upshift at WOT? - Chevy Impala SS Forum
Reply
 
LinkBack Thread Tools Display Modes
post #1 of 19 (permalink) Old 01-25-2019, 10:44 AM Thread Starter
Senior Member
 
Join Date: Sep 2007
Location: Carbondale, IL
Posts: 729
 
Third gear doesn't upshift at WOT?

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.)

--'94 Caprice "SS" wagon, 0.30 over, high-volume oil pump, LT4 hot cam, 1.6:1 rockers, ported aluminum Corvette heads, shorty headers, PCM4Less tune, 4.10s, shift kit, side-exit dual exhaust with Flowmasters, OR X-pipe, F-body gauge cluster, Bonneville front and rear seats (working electrics), Bravada console shifter, Bilsteins, 12.7:1 Impala steering box, Boss 338s with 255/45R20s, bunch of other stuff I'm forgetting.
--'04 Mustang Cobra, '15 Audi S4
--1125R, 1050, VMax, VFR800, DRZ-400E
TheFleshRocket is offline  
Sponsored Links
Advertisement
 
post #2 of 19 (permalink) Old 01-26-2019, 10:50 AM
Senior Member
 
KW Baraka's Avatar
 
Join Date: Feb 2001
Location: South Central Texas....By Way of the South Side of Chicago!!!!!
Posts: 20,277
 
This is a transmission issue.

Click the link below and see issue #6. THIS....is your problem and your tranny requires a rebuild.

https://www.impalassforum.com/vBulle...-failures.html

KW

1996 BBB SS, 398ci Solid Roller LT4, TorqHead 24x Conversion


1995 DCM SS, LS3, Texas Speed 260cc PRC heads, Lingenfelter GT1-1 cam, V-max 90mm TB, Headman 1 7/8 LT Headers, 2 1/2" cat-back, 3200 Circle-D TC, 3.73 gears -- 493HP/434TQ @ the wheels (Daily Driver)


2014 Chevy SS; Low Lash Solid Roller 429ci LS3 -- 548HP/464TQ @ the wheels....

KW Baraka is offline  
post #3 of 19 (permalink) Old 01-26-2019, 11:16 AM
Senior Member
 
Z09B4U's Avatar
 
Join Date: Jul 2015
Location: Canada
Posts: 832
 
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.

Z09B4U
Z09B4U is offline  
 
post #4 of 19 (permalink) Old 01-26-2019, 11:27 AM
Senior Member
 
95wagon's Avatar
 
Join Date: Jul 2001
Location: Vancouver B.C. Canada
Posts: 4,462
 
As said above.
Attached Images
 


The First
LS7 T56 6 Speed Wagon
Katech cam , 550 rwhp
11.79 @ 120.65


LS7 T56 drag video
My Wagon
My W-31 Cutlass
95wagon is offline  
post #5 of 19 (permalink) Old 01-26-2019, 02:55 PM
Senior Member
 
Join Date: Sep 2005
Location: (718)-
Posts: 1,423
 
Quote:
Originally Posted by 95wagon View Post
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.

1g1bl82p7rr127841 Rust In Pieces, Rest In Peace
They are NOT Lying to You
You are NOT Lying to Yourself
You are Being Lied to - BY Your Self
Alone aka The Last Psychiatrist
Marky Dissod is offline  
post #6 of 19 (permalink) Old 01-26-2019, 03:13 PM
Senior Member
 
95wagon's Avatar
 
Join Date: Jul 2001
Location: Vancouver B.C. Canada
Posts: 4,462
 
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?


The First
LS7 T56 6 Speed Wagon
Katech cam , 550 rwhp
11.79 @ 120.65


LS7 T56 drag video
My Wagon
My W-31 Cutlass
95wagon is offline  
post #7 of 19 (permalink) Old 01-26-2019, 03:39 PM
Senior Member
 
Join Date: Sep 2005
Location: (718)-
Posts: 1,423
 
Quote:
Originally Posted by 95wagon View Post
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?

1g1bl82p7rr127841 Rust In Pieces, Rest In Peace
They are NOT Lying to You
You are NOT Lying to Yourself
You are Being Lied to - BY Your Self
Alone aka The Last Psychiatrist
Marky Dissod is offline  
post #8 of 19 (permalink) Old 01-26-2019, 04:23 PM
Senior Member
 
95wagon's Avatar
 
Join Date: Jul 2001
Location: Vancouver B.C. Canada
Posts: 4,462
 
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


The First
LS7 T56 6 Speed Wagon
Katech cam , 550 rwhp
11.79 @ 120.65


LS7 T56 drag video
My Wagon
My W-31 Cutlass
95wagon is offline  
post #9 of 19 (permalink) Old 01-26-2019, 05:23 PM
Senior Member
 
Z09B4U's Avatar
 
Join Date: Jul 2015
Location: Canada
Posts: 832
 
Stock tire 27" 4.10 gear.
29" 4.10

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


Quote:
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.



Quote:
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).


Quote:
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

Z09B4U

Last edited by Z09B4U; 01-26-2019 at 05:58 PM. Reason: 29" #
Z09B4U is offline  
post #10 of 19 (permalink) Old 01-26-2019, 05:23 PM
Sophomore Member
 
Join Date: May 2003
Location: Huntsville, AL
Posts: 8,211
 
Send a message via AIM to sherlock9c1
+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.

"The unexamined life is not worth living." - Socrates
sherlock9c1 is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Chevy Impala SS Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome