4L80E WOT shifting problem. 1st-2nd bounce rev limiter!

[TransAm-Z]

I'm not sure if there is something wrong with the tune or my intermediate clutches are starting to fail... Problem is the 1st-2nd gear shift is not happening soon enough and engine is bouncing off rev limiter. I have posted a log and a screenshot showing that the "GM.GEAR" PID is not switching to 2nd gear until around 63mph or 7440 rpm. The tune I posted shows the 1st-2nd WOT shift commanded at 6200rpm and the part throttle shift should happen at 50mph. Also if you notice 2nd-3rd gear is off from the tune as well. WOT=7000rpm and it is actually shifting around 6465rpm.

Does the GM.Gear PID represent when the gear is commanded to shift or does it represented what the pressure switch sees in the trans?

Thanks!

15692

[joecar]

You need to set the WOT downshift MPH below the corresponding WOT upshift MPH...

i.e.
- D0925-27 should be below D0910-12,
- D0930-32 should be below D0915-17,
- Do935-37 should be below D0920-22;


also, set the WOT shift RPM's lower than what you have (say 5000 rpm), and then when you do get the WOT shifts occuring bump the WOT shift RPM's back up...

but note that both WOT shift RPM and WOT shift MPH must be met, so keep either one of them lower than what is needed (but keep in mind what I said above).


Also, look at some 4L80E files and set B4601 to be similar.

[joecar]

...

Does the GM.Gear PID represent when the gear is commanded to shift or does it represented what the pressure switch sees in the trans?

...
GM.GEAR represents when the PCM switches the solenoids.


There are no gear pressure switches in the 4L80E or the 4L60E (the pressure switches read the pressures in response to the manual valve, not the current gear).

[TransAm-Z]

Thanks for the fast reply Joecar!

I am still a little confused though as the "stock" Silverado tune from Holden-Crazy I started with has the tables very similar to mine. (D0910 - D0925)

What you are saying makes sense to me, I just don't understand why there are multiple tables being used... I assume from what you stated above that the PCM will look at both tables (RPM AND VSS WOT) and shift upon the last criteria meet?

15696

[hog]

Thanks for the fast reply Joecar!

I am still a little confused though as the "stock" Silverado tune from Holden-Crazy I started with has the tables very similar to mine. (D0910 - D0925)

What you are saying makes sense to me, I just don't understand why there are multiple tables being used... I assume from what you stated above that the PCM will look at both tables (RPM AND VSS WOT) and shift upon the last criteria meet?

15696

Yess, speed and rpm MUST be met before an upshift will be performed. Kinda like needing a bullet and a trigger pull in order to fire a gun.

In this equation Bullet + Trigger Pull = Gunshot
Bullet=Speed
Trigger Pull=RPM
Shift=Gunshot

peace
Hog

[joecar]

Thanks for the fast reply Joecar!

I am still a little confused though as the "stock" Silverado tune from Holden-Crazy I started with has the tables very similar to mine. (D0910 - D0925)

What you are saying makes sense to me, I just don't understand why there are multiple tables being used... I assume from what you stated above that the PCM will look at both tables (RPM AND VSS WOT) and shift upon the last criteria meet?

15696Some of the stock truck files contain "wrong" values (and cheat by using the Throttle Kickdown tables, which interferes with the PT upshift/downshift tables).


Yes, PCM looks at 3 criteria for WOT shift: WOT RPM, WOT upshift MPH, and WOT downshift MPH...

WOT RPM and WOT upshift MPH must both be met... and WOT downshift MPH must be below WOT upshift MPH.

[joecar]

lol, cars and guns, Hog has an interesting analogy :cheers:

chamber a round = WOT MPH
pull trigger = WOT RPM

(or vice-versa depending on which one is met first)

[TransAm-Z]

Thanks for the help! I'll make sure the bullets are in the gun this time=]

I will test it tonight to see if all is better. Any idea what causes the trans to shift at all when these tables are messed up?

Amazes me that I haven't blown this thing up yet! This trans has made about 50 passes @ aprox 1000 RWHP...