How to not tune a 4l60

[witty_name]

So, I got tired of the 4l60e's downshift hesitancy in my '04 Suburban and decided to do something about it. Story time!

I was struggling to keep up with my brother in Jeep of all things on a recent road trip. This was because the cruise control would get lost the in slop between where it stops making more and power and finally downshifts. I started just locking it in 2nd or 3rd depending on speed and hilliness and just thought that these things are dogs. I looked into 8 or 10 speed upgrades and then I almost got creamed by a semi at the end of a steep on ramp because I didn't know you had to floor it, floor it to get a 2-->1 shift. This got me to look at the shift points and boy are they dumb.

So I burned some tax return money on a tuner and got to work. copied the 3--->2 shift points on to the 2--->1, adjusted for gear ratio and problem solved, ish. There was still that large zone of slop between no more power and the gear shift and trying to get rid of that is where my problems started. Basically I was vibe tuning the downshift points to come in sooner and made fun errors like commanding upshifts into a gear that was calling for a downshift at that speed. Playing with TCC lockup settings and adding 2nd gear lockup only compounded the problem. Every fix caused new issues and eventually the ECU gave up threw a CEL and commanded third no lockup all the way home from work last week.

So went back to the drawing board and created a spreadsheet to track and visualize what I was doing. I kept adding tables every time I wished I knew some relationship between values. After some tedious work I got the shift tables good enough, added a sheet for TCC lockup and got that where I wanted and then a sheet to combine the effects of both and WOW! The truck feels like a whole new beast, I still have some data logging and fine tuning to do but I have completely changed the character of my rig. I highly recommend doing this to your truck/SUV, it made more of a difference than swapping a 3800 SC into an NA 3800 car I used to have, just be smart about it.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

A lot of work, but the end result justifies the effort. Bravo to you.

 

[Marky Dissod]

GM's V8 transmission shifting philosophy is painfully obvious,
and 6-, 8-, & 10-speed automatic transmissions only encourage and exacerbate it
(so much so, that GM's shifting programming is chiefly responsible for breaking several thousand L87s):

1. UpShift as soon as possible, so long as the engine makes enough torque in the next gear to not decelerate
that'd be a stupidly early upshift, if the car started decelerating, yeah?

2. make the driver push down on the throttle quite a lot before a DownShift is commanded
since most drivers are ANTI-enthusiastic about driving, and prefer more MpGs & less NVH,
DownShifts are delayed as far as reasonably possible.

For enthusiasts, net effect is an uncooperative transmission that discourages enthusiastic driving,
and especially in the case of the L87, makes the engine do too much work at very low RpMs
ostensibly to improve MpGs and reduce NVH.

... went back to the drawing board and created a spreadsheet to track and visualize what I was doing.

Could've saved yourself several steps by using a 2D line graph representation,
instead of the spreadsheet representation.

You should be able to select how the values are visually represented.
HPTuners allows you to select a 2D line graph above the numbers,
so that manipulating the graph manipulates the numbers shown below.

 

[Marky Dissod]

... almost got creamed by a semi at the end of a steep on ramp,
because I didn't know you had to floor it, FLOOR IT to get a 2Dn1.

For the vast majority of drivers who multitask while driving, an unresponsive transmission is a feature, not a bug.

The way to make the transmission cooperate and encourage the driver
instead resisting / discouraging the driver, is as follows:
(*note #1 & #2 in the previous post)

1. Raise GM's early UpShifts
Obviously for common/low throttle angles, only raise them a lil bit.
As the throttle increases, raise them more, to prevent early UpShifts.
Obviously, don't raise them too high / past the engine redline.

2. AFTER raising the early UpShifts, raise the DownShifts closer to the UpShifts
The wider the gap between an UpShift and its corresponding DownShift,
the less enthusiastic the experience for the driver, the less responsive the transmission,
the more time the engine spends at lower RpMs than the driver wants.
This improves POTENTIAL MpG on a CAFE test, but in the real world,
the driver just opens the throttle until a downshift finally occurs.

The closer the gap between an UpShift and its corresponding DownShift,
the more enthusiastic the experience for the driver, the more responsive the transmission,
the more time the engine spends where the driver wants it to be.
This either forces the driver to have more foot discipline to avoid DownShifts,
or is more appreciated by the driver as the transmission responds more eagerly.

That, by the way, is where I derive the term Smiles per Gallon -
making the transmission more eager to please the driver
reduces peak potential MpGs, in exchange for more potential fun.

THE FIRST SHIFT TABLE YOUR CHILDREN USE TO LEARN TO DRIVE
SHOULD BE EVEN MORE UNRESPONSIVE THAN GM OE.

 

[OR VietVet]

Welcome to the forum from Oregon.

 

[Marky Dissod]

I was struggling to keep up with my brother in Jeep of all things on a recent road trip.
This was because the cruise control would get lost the in slop between where it stops making more and power and finally downshifts.

1. The OTHER reason why (that this thread should not address at length) is because
GM ALSO under-gears the axle(s) in yet another attempt to lower the RpMs and improve MpG.
Your '04 Suburban likely came with 3.42 or 3.73. You likely upgraded to 3.73 or 4.10.
I'll end by stating that under-gearing is a strain on both the engine and the transmission,
which goes unnoticed by unenthusiastic drivers who don't bother comparing to anything else.

2. Depending on throttle angle, Cruise Control is programmed either as or MORE conservatively,
compared to Normal, with a few exceptions, to preserve the POTENTIAL MpG capacity,
reduce NVH, and generally make the trip as predictably banal as possible.
One thing I'm pretty sure enthusiast 'vette drivers share with every other type of driver:
They do NOT use Cruise Control for enthusiastic driving of any type under most circumstances.

At least in my case, I prefer Cruise Control to only be slightly more aggressive than GM OE.
Prefer not to chance that the Cruise Control will surprise with excess responsiveness.

Where GM prefers to discourage the driver by making the transmission hesitant,
I prefer the Normal Shift table to have a bit of a Jekyll / Hyde quality:
more throttle = more responsiveness

Tow / Haul should be programmed to protect the engine, transmission,
AND the load being Towed / Hauled. MpGs are NOT be a major priority here.
This shift table can also be improved upon compared to GM OE, but again,
better axle(s) gearing helps more, up to the point of diminishing returns.

However, I do not Tow / Haul at all whatsoever. Instead, I drive like a Jacques-arse.
So I programmed Tow / Haul more like Sport / Performance. (Did NOT say Race / Qualify).
Nearly every single point is even higher than in my post-tuned Normal Shift table.
I do get nervous when I lend my vehicle to trusted friends,
who I warn in advance to avoid Tow / Haul use unless needed.

 

[Marky Dissod]

Most of you may not have considered the possibility that
GM pushed conservative unresponsive transmission tuning too far.
So much so, that - likely coupled with cheap bearing selections -
Not surprised that thousands of L87s have suffered for GM's subservience to CAFE.

It is precisely why I have stated that tuning is not just for enthusiasts.
Tuning - not only of the shift tables, of course - isn't just for fun.
Proper through tuning also improves durability and longevity.

Get tuned. No one who has ever gotten a thorough proper tune has ever regretted it.