Hello
I had the pleasure to go to the track last night and find that my trans is not shifting correctly at WOT
it goes to 2nd at 22mph
it goes to 3rd at 40 mph
and it basically just coast through the track no matter what we did.
the tune commands it to shift to 2nd at 40mph and 6400rpm and to 3rd at 70mph and 6500
the tranny is a 4l80e with a vacuum modulator and a 3800 stall. we are looking at the tune with attention to detail to make sure its not the issue.

what are some possible causes for this to happen.
I see it happen in normal driving conditions as it goes to second right away...in fact feels too soon.

the PCM is a 98 and it has the 4l60e file with some tweeks to the harness so the car thinks its a 4l60e. the thing that is weird is that it has the command to do the above shift points but still short shifts no matter what.

what do you experts think?

 

37 views and no one has a comment?

 

i had the same problem with my 80e when i did gear change. changed for speedo but had to change the tables for shift speed and rpm

 

What tire size and rear gears? Its probably off in the speedo section.

 

28 inch tires and 4.11. Did Rick send youth tune slow67? I saw he did use those values. Also the vss is plugged on the rear sensor. It shifts when doing a roll but will shirt shift from a dig to quick

 

Yeah he did, thanks. Hmmmmm its possible its a TPS sensor on its way out....do you know anyone you can borrow a TPS sensor to see if that helps? Also have him send me a log (showing commanded gear).

 

I have another tps sensor I will bolt on. And will see what happens. Does it make a difference that THe tranny has different gearing than 60e?

 

No, its doesn't match on my car either and its my daily (Its been this way for over a year)

As long as the code is deleted and shift points are correct it shouldn't matter. Thats why I'm thinking it may be TPS since from a roll it doesnt do it vs from a dig it does (more total TPS movement).

 

I sent you the logged run of it short shifting. Did you see anything that caught your eye?

 

This May or may not applie to you but the symptoms are similar so something to look at.

PO121 CODE OR QUICK SHIFT 1-2-3-4 at WOT by 40 MPH FIX
Found this info on another forum and I know many people have popped up with this issue and wanted a fix. This would appear to be it. Hope it helps someone.

The curse of the P0121 Code... This code is infamous for giving people with larger cams fits...everything from traction control troubles, to shift point issues to just the good ole' P0121 code showing up for seemingly no reason making people scramble to purchase new Throttle Position sensors, adjust their set screws, etc, etc.

Before I go any further have a gander at the DTC information provided by LS2.com

http://www.ls2.com/boggs/dtcs/DTC%20P0121.htm

To outline a few key points

Quote:
The MAP is greater than 65 kPa

Quote:
The predicted throttle angle does not match the actual throttle angle

Quote:
All conditions present for 20 seconds

Now, that 65kpa map figure comes into play in nearly every LS1 Car/Truck because its the max map setting in most of the calibrations for the sanity test as shown here


Under normal circumbstances a stock cammed A4 will probably idle at around 35-40 map. When switching to a larger cam with more overlap your map readings could go up to as high as 70 or more kpa map which is way outside of the normal boundries. On a stock cammed car you'd probably need to be at around 30% tps to hit that same map number which is where that predicted throttle angle quote comes into play.

Now onto the last quote the 20 second timeframe. This will Usually come into play more often than not at idle with large cammed vehicles because many times your steady state map will be within the map sanity guidelines so there is a good possibity you might not see this code pop up immediatly.

There are a few ways you can cure this issue
a. Do as suggested in the help file which is to just set the min to 0 & max to 100
b. Adjust them to YOUR liking so you'll be within a reasonable limit. This will help determine if there IS a real issue with your TPS sensor later down the line.

So there you have it, as good an explanation I can come up with for that bastard code. So the next time you go WOT in your auto LS1 with a large cam & you go from 1st to 4th by 40mph or just a nagging p0121 code for no obvious reason you now have the info needed to fend it off.

 

Wow that is great information. Thanks for posting it here. I will ask Rick who is Tuning the car to read it and see if he can figure it out.

 

I thought I had looked at that table....Give that a try.


Not really.....the log a ton of parameters so it was only grabbing logs 5 times a second. Give the above a try.

 

It was not throwing the code but i will deffinitly give it a try

 

Performabuilt:
I want to thank you for posting this here again. The tuner and I got together today and saw that it was indeed trowing that code PO121 and changing the values as posted helped the tranny shift as it should. I am going to take it to the track and see the real effect there bc it was having the problem at WOT, we did a few pulls in the street and it was shifting flawless.
I am very happy right now on how it is behaving in the street. so far I will sping the tires on a 35 roll with the 345 on the rear. it is very Fun and feels like a different car....
cant wait to try it at the track.
Whooo HOOOOOOO!!!!!!

P>S what should the car in my sig run at the track approximately?

 

You are always welcome thats what Im here for to help whenever I can , Good luck at the track