Downshifting pointers needed

[Pocket]

Now that I have my upshift points and torque converter lockup points set how I like them (this thing is shifting like a dream :happy-dancing: ), I'm looking at some downshifting changes.

Some background... My old tunes had two settings with downshifting (daily driver and tow setting). As my truck slowed, the trans would downshift from 4th into 3rd. This came in handy in the mountains, especially when towing a load. The only issue I had with the downshifting was the torque converter remained locked as it downshifted, often resulting in a very jarring and harsh downshift (also heard it wasn't good for the transmission).

So my question, can I tune a 4-3 downshift that unlocks the torque converter, then locks it back up for a smoother downshift?

[cleatus12r]

Two things to try. I say "try" because I've noticed that there is quite a difference between PCM families and how they react to certain changes.

There are three converter lock/relock delay parameters for the 4-3 downshift. These are listed in seconds. These work well for PMT1 boxes but I know that your tunes are TNAA7 based so the best I can say is to try.

The best solution (but it won't reapply the TC clutch), is to raise the unlock speed in the 3rd gear function to the 4-3 downshift speed. Don't raise it above the apply speed, because it just won't lock then.

[Pocket]

What are those converter lock/unlock parameters called?

[cleatus12r]

Delay Converter Lock after 4-3b
Delay Converter Lock after 4-3
Converter Relock Delay after 4-3

[Pocket]

Ahh, I see! Thanks Cody.

Now of course that brings up an all new question. What's the difference between Delay Converter Lock after 4-3"b" and Delay Converter Lock after 4-3? I noticed it's there on the upshifts too. Now I've changed the delay converter lock on upshifts in the "non-b" set, but not in the set with the "b" tag. Does that make a difference? Do they both need to be the same?

[Pocket]

Well I tried those parameters and increased the time to delay the lockup on the 4-3 shift with no luck. It just refuses to unlock the torque converter when it downshifts. The only change that I saw was that the jarring was slightly less if I was completely off the pedal, and it almost downshifted smoothly (just not quite as smooth as I wanted, still a bit of jarring). The problem that still remains is that if I'm going uphill, and have my foot very lightly on the pedal (light enough that it's registering the pedal is applied, but not enough to maintain speed going up a steep hill), the jarring is still extremely harsh. So for that scenario, it made no difference at all.

Just to note, that second scenario with the pedal lightly applied has always had a much harsher downshift, even with my old tunes. So I'm guessing that it's something to do with the TNAA7 based tuning. :shrug:

I also tried the other suggestion you gave Cody, by raising the unlock speed in 3rd, but that results in a big RPM drop when shifting into 4th as the torque converter re-locks, and I'm stuck lugging the engine going uphill. :cry-blow:

If there's any more suggestions, I'm open to try them. Right now I seem to have hit a brick wall, and can't find a way around it, other than disabling the clutch coast function like it is in stock VDH2 tuning. But I really would like to have a working downshift solution for this. Reason being is that up in the mountains, some of the roads wind around quite a bit, so if I'm at a lower speed and let off the pedal without a working downshift, the engine just coasts until I re-apply the pedal, and I'm stuck with lag as I'm waiting for the RPM's to climb and turbo to spool back up. It really does make a difference, as the turbo seems to light up quicker if the RPM's are kept up at least a little bit more.

Altitude sucks for tuning, makes things much more difficult :cursin:

[907DAVE]

I am experiencing a similar issue with my 4-3 downshift, I was going to try and tackle this issue when I get the emulator. I feel you pain when trying to fine tune things with no real progress.

Not trying to sound to dumb here........have you tried backing down the 4-3 shift pressure?

[Pocket]

I am experiencing a similar issue with my 4-3 downshift, I was going to try and tackle this issue when I get the emulator. I feel you pain when trying to fine tune things with no real progress.

Not trying to sound to dumb here........have you tried backing down the 4-3 shift pressure?
I could try that. It's set at whatever stock is. :hmmm:

[907DAVE]

Another thing worth trying is the parameter Downshift Slope into 3rd.

I do not know what this will do but might be worth a shot.

[GTS]

What transmission are you running? Could it be the way the hard parts are set up in the transmission? Orifice size for the TC lockup, valve body set up etc?

[Pocket]

What transmission are you running? Could it be the way the hard parts are set up in the transmission? Orifice size for the TC lockup, valve body set up etc?

I got it figured out a while back. It wasn't a transmission issue (I'm running a BTS), it was simply tuning. I had some pressures that were higher than stock, and on the 4-3 downshift it would slam hard. Knocked down the pressures, increased the delay slightly, and afterwards I could barely feel it.

Funny part is, after all that effort, I don't even use the downshifting anymore. My shift strategy is very close to stock now. Before I had a problem with too much fuel at lower RPM's, so my shift strategy was designed to keep the RPM's up. Now I don't have the fueling problem, so I don't care about lower RPM's as much. Besides, with the amount of fueling I'm throwing at lower RPM's and lower throttle position, it takes quite a bit of throttle movement just to get the fueling up. At that point, the PCM is already commanding a downshift. So then my RPM's catch up, I don't get a lugging engine, I don't get black smoke, and my fueling kicks in at that point.

Problem solved on my end, and the truck drives and shifts like a dream. I can always tell if my tuning and shifting is spot on when my wife comments about how well it drives.

[907DAVE]

Before I had a problem with too much fuel at lower RPM's, so my shift strategy was designed to keep the RPM's up. Now I don't have the fueling problem, so I don't care about lower RPM's as much. Besides, with the amount of fueling I'm throwing at lower RPM's and lower throttle position, it takes quite a bit of throttle movement just to get the fueling up. At that point, the PCM is already commanding a downshift. So then my RPM's catch up, I don't get a lugging engine, I don't get black smoke, and my fueling kicks in at that point.



Very nice Curtis!

That actually took me quite a bit of time to get dialed in........in all situations.

[GTS]

Cool. Glad to hear you got it resolved and a bit on how you did it. Just curius what gearing and tire size are you running? I'm kind of looking to do what you did as my gearing is very tall so a light roll in results in black smoke before it'll down shift. I'm thinking of dialing in the fuel to start ramping up at the rpm that actually starts seeing some decent boost. Which with my gearing is a bit higher in the speed range. I'm looking to do this especially in my DD tunes where I don't care so much about power as I do no smoke and mileage.

[Pocket]

Very nice Curtis!

That actually took me quite a bit of time to get dialed in........in all situations.

You saw some of my earlier versions a few months back. Since then I've really been dialing it in nicely.

Last week I had a chance to try my newest configurations in the mountains. As a test, I switched back and forth between my tuning and stock. My tunes ran slightly lower EGT's while climbing a mountain pass, and were quieter. Even in stock form I could hear a slight timing rattle. In my tunes, there is no rattle.

Smoke is nearly identical between stock and my tunes while driving up a mountain pass at 10K feet. I'm stoked that it's working. Shifting worked exactly as I wanted it to also.

Next step is taking in for dyno runs and emissions testing. I want a 350 hp tune on stock sticks that passes emissions. :cheesy smile:

[Pocket]

Cool. Glad to hear you got it resolved and a bit on how you did it. Just curius what gearing and tire size are you running?

I'm running 36" tires with 4.30 gears. It's almost identical to stock in regards to speed vs. RPM's.

My truck came stock with 265/75r16's and 3.73's. In stock form, my truck would see 2000 RPM's at 70 mph. With my current setup, I see 2000 RPM's at 69 mph, so it's very close.

I'm kind of looking to do what you did as my gearing is very tall so a light roll in results in black smoke before it'll down shift. I'm thinking of dialing in the fuel to start ramping up at the rpm that actually starts seeing some decent boost. Which with my gearing is a bit higher in the speed range. I'm looking to do this especially in my DD tunes where I don't care so much about power as I do no smoke and mileage.
Well, I did the opposite of what you are planning. :whistle1: Only because I struggled with the exact same thing for a long time, and finally took a different approach. For me, it's not the tires or gearing, it's the altitude. So it made my learning curve pretty tough to figure out fueling, smoke control, egt's, etc.

If you want, I can shoot you an email with some screen shots. I see you posted your email addy in the other thread. Would you be ok with me shooting you a message? I'd be glad to help you out.

[GTS]

At this point in time I'll accept any help I can get! I've been messing with the software for a few days now but haven't really done much as far as putting a tune together. More just moving things around and familiarizing myself with how it all works. Thanks so much for your input and willingness to help!

[Pocket]

You have mail!

[GTS]

Thank you so much you guys for your e-mails. I've been spending WAY to much time on this stuff lately! :hehe: I'm just so excited to get going on this tuning! I'm looking over your guys' e-mail now though I REALLY need to be getting to bed! It's almost 2:00 in the morning and I need to get up around 7!

[2006nytro]

ok got a question didnt see a need to start a new thread. when tuneing a trans whats the main things you use to adjust it.

is it rpm vs speed? i would think thats most of it? and is it you set a sertan shift point how does the trans know to shift difrent say at WOT,or just creeping up speed slow? is it a calculation the pcm makes?

[907DAVE]

Shifting is determined by comparing APP (pedal position) and MPH.

So basically the harder you press the go pedal - the longer it will take to shift. When you are WOT, it will shift at a preset maximum RPM - which you can change.

If you want to adjust the quickness/firmness of a shift there is a whole slew of different ways to do it.

[strokeorcroak]

THis is getting interesting very fast.... I cant wait!

[winniety]

I really don't know
just post here keep an eyes on this topics:shrug: