Transmission control unit upgrades/customization

longassname · Post by **longassname** » Mon Dec 14, 2009 4:24 pm

I'm starting this thread as a place for people to dicuss what modifications they might want made to / be able to make to their tcu's.

The transmission control unit is the computer which controls pretty much everything the 4eat transmission does. It can't make it do anything the hardware is not capable of but it can make it do anything the hardware is capable of. I point that out because mechanical deficiencies are best overcome by mechanical upgrades; however, sometimes there is still room to improve them through the software. For instance, the high clutch in an SVX slips under light cruise and as a result the cars burn out high clutches and brake bands regularly. I upgrade the high clutches and rework the valve body to increase apply pressures to increase the torque carying capacity of the transmission through mechanical upgrades.

Phile Skuse, who's website is: http://www.alcyone.org.uk recently published the line pressure control maps for the SVX and there is some room there to increase the line pressure under light cruise in 4th gear thus increasing the torque carying capacity of the transmission under the conditions where it normally slips and causes transmission failure. This isn't as good as upgrading the transmission but it could certainly extend the life of SVX transmisisons without having to pull them out and send them to me. If there is a failure history with some kind of pattern like this with the legacy maybe we can address it too.

Do you like when your car shifts? There are shift maps which tell the transmission to shift according to vehicle speed and throttle position. These can be modified to hold particular gears longer, make it easier to downshift into particular gears, etc, etc. With the SVX I was able to make the car much sportier to drive around town while improving city fuel economy by 2 to 3 mpg by making it easier to downshift into 1st and holding 1st and 2nd gear longer.

Have performance camshafts? Full throttle shift points are controled by rev limits which are specified for each gear. These can be set to whatever you want.

The atf temp warning light doesn't come on until your transmission is already burning up and overheat mode doesn't come on until after that. I like to bring these down to 212 degrees F so you actually get a warning and the transmisison control unit starts saving your transmission before it's too late.

I haven't been modifying torque converter lock up but could if that's desired. That's all that comes to mind right now but if I missed something you want just bring it up. That's what this thread is for.

I have, by the way, been making my modifications to the SVX tcu public. The transmission control unit needs to have a socket installed into it and a surface mount resistor moved before it can be upgraded. It's best if this is done by someone skilled so I suggest sending it to me to start with but you don't have to. The information will be made public so if you want to do it yourself you can. It just comes out cheaper, easier, and faster to have me do it for you if I'm making an off the shelf chip that matches what you want. I also sell just the chips so if you want to do the desoldering and soldering yourself you can make the upgrade without having to invest in a programmer or start learning hex.

Here's the link to the page on my website with the SVX TCUs. There are graphs of the Shift maps for various SVX's there and of my modifications to them. As we get further along with a wishlist of changes I will post before and after graphs here of what I am doing to make those changes. I expect I'll be able to develop the changes as quickly as the community is able to come to a consensus on what you want.

http://www.ecutune.com/tcu.htm

Post by **Legacy777** » Mon Dec 14, 2009 7:18 pm

Michael,

Looks like some good comments and suggestions. I'm not sure if there's anything else that would need to be modified, but we'll see what others have comments on.

ericem · Post by **ericem** » Mon Dec 14, 2009 8:11 pm

A major thing I would like. 4th gear I always want it locked up and I want it to always downshift to atleast 3rd gear when I give more then 20% throttle. Right now even on the highway ALWAYS in 4th gear until I almost floor it. Both legacy's I have had do this! Also in the city alot of times I am driving around in 3rd unless I go below 40km/h. Seems like a waste of load on the motor to accelerate HAVING to use boost just to accelerate at the same rate I could in 2nd gear with extremely minimal throttle and no boost!

Lunatech · Post by **Lunatech** » Tue Dec 15, 2009 1:32 pm

I have never had a Subaru with an automatic, but I have had other brands though, and none of them would ever kick down out of OD if the cruise control was in use, not without intervention from the driver any way.

What I mean is, when driving on the highway using cruise control at say 65 mph, you encounter a mountain that is a 6%grade for 1 mile or more. My Voyager or Cutlass would never automatically shift down from OD. Not a big deal in the Olds with it 's 3.8, but the Plymouth with it's Mitsubishi built 3.0 and being a van would actually bog till it stalled if you let it and never shift down.

I don't know if the 4eat in the Subaru will or not, but if it won't, that might be something that drivers of automatics would benefit from.

93Leg-c · Post by **93Leg-c** » Tue Dec 15, 2009 9:03 pm

To help emergency stopping, I'd like the auto tranny to be able to downshift into 1st gear at 40 mph rather than when it actually kicks in, which is about 20+ mph.

To echo what ericem posted, it would be nice to be able to have the tranny downshift when on the freeway at part throttle response rather than having to floor it. For me, a 20-25% throttle response kickdown would be great.

longassname · Post by **longassname** » Tue Dec 15, 2009 9:56 pm

There is a seperate shift map for each gear of each stick position. It sounds like what you are wanting is for it to actually shift into first from 3rd if you move the selector into first so that you get engine braking with high revs. We can do that by adjusting the stick in 1 3 to 2 and 2 to 1 maps as long as the resulting engine speed won't make it hit the 1st gear rev limit.

Sounds like maybe the legacy is as relectant to kick down to 2nd or 3rd as the SVX is to kick down into 1st. I guess that's Subaru's idea of economy but it always ends up actually costing more gas because we end up flooring the car a lot. We can easily enough fix that.

93Leg-c wrote:To help emergency stopping, I'd like the auto tranny to be able to downshift into 1st gear at 40 mph rather than when it actually kicks in, which is about 20+ mph.

To echo what ericem posted, it would be nice to be able to have the tranny downshift when on the freeway at part throttle response rather than having to floor it. For me, a 20-25% throttle response kickdown would be great.

Post by **Legacy777** » Wed Dec 16, 2009 7:23 pm

When my car was an automatic, I found that if I floored it would kick down a gear with little to no hesitation. However some of the issue is it'll kick down into first, rpms would be at 5500, and then it would shift at 6500.... So a part throttle kick down to next lowest gear would have been nice vs. a 2 gear kick down and balls out revving.

I'm not sure what categorizes "emergency" stopping. That may be hard to define normal and emergency stopping, unless you do it by what position the gear selector is in.

From my experience the Legacy transmission would not go into 1st gear when slowing down unless you pretty much came to a complete stop. It would stay in 2nd. That may be what Len & Eric are wanting...

klin7757 · Post by **klin7757** » Wed Dec 16, 2009 8:15 pm

does anyone know if the svx tcu's shift maps are more aggressive than the legacy? i just came across an svx in a junk yard and it has the tcu.

ericem · Post by **ericem** » Wed Dec 16, 2009 9:18 pm

longassname wrote:There is a seperate shift map for each gear of each stick position. It sounds like what you are wanting is for it to actually shift into first from 3rd if you move the selector into first so that you get engine braking with high revs. We can do that by adjusting the stick in 1 3 to 2 and 2 to 1 maps as long as the resulting engine speed won't make it hit the 1st gear rev limit.

Sounds like maybe the legacy is as relectant to kick down to 2nd or 3rd as the SVX is to kick down into 1st. I guess that's Subaru's idea of economy but it always ends up actually costing more gas because we end up flooring the car a lot. We can easily enough fix that.

93Leg-c wrote:To help emergency stopping, I'd like the auto tranny to be able to downshift into 1st gear at 40 mph rather than when it actually kicks in, which is about 20+ mph.

To echo what ericem posted, it would be nice to be able to have the tranny downshift when on the freeway at part throttle response rather than having to floor it. For me, a 20-25% throttle response kickdown would be great.

Yes, and I find 4th gear NOT locked up is just a waste of gas. It is MUCH better off just going to 3rd gear then it is staying in 4th with the torque converter not locked up.

I know with SVX's though there first gear takes you all the way to 50mph where with our cars takes you to 40mph.

longassname · Post by **longassname** » Thu Dec 17, 2009 12:00 am

You can't swap the tcu's.

klin7757 wrote:does anyone know if the svx tcu's shift maps are more aggressive than the legacy? i just came across an svx in a junk yard and it has the tcu.

klin7757 · Post by **klin7757** » Thu Dec 17, 2009 1:22 am

[quote="longassname"]You can't swap the tcu's.

too bad. plugs looked similar. oh well thanks for the info.

93Leg-c · Post by **93Leg-c** » Thu Dec 17, 2009 6:01 pm

Legacy777 wrote:I'm not sure what categorizes "emergency" stopping. That may be hard to define normal and emergency stopping, unless you do it by what position the gear selector is in.

From my experience the Legacy transmission would not go into 1st gear when slowing down unless you pretty much came to a complete stop. It would stay in 2nd. That may be what Len & Eric are wanting...

What I mean by "emergency stopping" is anything requiring additional slow-down of the car to assist maximum braking so that the front bumper doesn't assist in the stopping.

Or, for some reason, if the brakes partially or completely failed the ability to downshift into first gear from 40 mph would be nice to have.

I guess what I'm getting at is if engine braking can be used to assist in slowing down it could mean a difference between getting into an accident or not.

But if it's going to take 10 seconds before first gear actually engages after manually moving the gearshift selector into 1st, then the downshift feature won't be of much help in a "must-stop-NOW" situation but it would still be helpful other situations.

ericem · Post by **ericem** » Thu Dec 17, 2009 6:43 pm

I see no issue with simply hitting the brakes. Of course engine braking could happen. I think there would be alot of work inluding switches for the tcu to do this, even then you would not always want it to do this. Could be even worse safety wise especially on snow and ice. Better off getting good pads and trying to steer away avoiding the accident.

Post by **Legacy777** » Fri Dec 18, 2009 6:44 pm

My transmission would downshift into the previous gear if I moved the gear selector into it almost immediately.

However, when I was playing with the trans dropping resistor and unplugged it, I found that the transmission would NOT drop down into the previous gear. In me playing with that, I ended up fubaring it up, as the transmission never reacted the same afterwards.

Lunatech · Post by **Lunatech** » Fri Dec 18, 2009 7:27 pm

I agree with ericem, using your brakes for braking makes good sense, I'm doin' it all the time. Compression braking definitely decreases wear on brake pads, but increases stresses on cv-joints, u-joints, transmission and engine. I would far rather replace brake pads than any of that other stuff. On the other hand, when I'm behind the wheel, I'm something of a control freak. If I put it in 1st gear at 80mph, by GOD I expect it to do as I command.

I'm still curious about the cruise control thing. Will the legacy automatically shift down without intervention from the driver while using cruise control?

longassname · Post by **longassname** » Fri Dec 18, 2009 7:51 pm

There are different shift maps for while in cruise control. It will do whatever the shift maps for cruise control whatever stick position you are in say to do. Cruise control maps tend to have wider ranges of operation without gear changes.

I'm not sure people are understanding yet just how many maps there are. There are a lot of shift maps--well over a hundred. There is a different shift map for each mode and each stick position and each gear transition..with all those exponents there are a lot of shift maps.

If you're in cruise control with your stick in D you will be using the cruise, stick in d, 1 to 2, 2 to 3, 3 to 4, 4 to 3, 3 to 2, 2 to 1 shift maps. When the car shifts is entirely a factor of %throttle (applied by cruise control) and vehicle speed. If you're cruising along in 4th gear and start going up a hill and the cruise control has to apply more throttle to maintain the speed it is set to and the throttle percentage passes over the plot of the 4 to 3 shift map then it will downshift into 3. If you were to compare the cruise control stick in d 4 to 3 map to the normal mode stick in d 4 to 3 map you would most likely find it would require more throttle to get it to kick down to third gear.

Lego · Post by **Lego** » Tue Dec 22, 2009 7:41 pm

a chip just like the svx chip would be great.

longassname · Post by **longassname** » Thu Dec 24, 2009 4:35 pm

Speaking of comparisons with the SVX TCU. I just looked at the 90 legacy TCU firmware and it looks like the Legacy has half as many "modes" and half as many shift maps as the US SVX TCU. I think Subaru went a little wild with the SVX TCU; they have different modes for different altitudes for example. Anyway I found the 90 legacy shift maps. The first one is at CA1E. The last one is at CDFB.

wtdash · Post by **wtdash** » Tue Dec 29, 2009 4:58 am

Michael,
You're familiar w/the Power Mode switch the non-US SVX's have, and the wiring mod for the SVX.

The Legacy version is posted HEREon the BBS.

I did this on my '90 (swapped in EJ22T and Turbo 4EAT), but it would only work when I swapped in a '93 Turbo TCU. It didn't work w/the '91 Turbo TCU I originally was using. I believe it was changed in '92?? Although I did have the Power mode/light w/the '90 NA and '91 Turbo TCUs.

Also, the 'custom resistor mod' listed HERE sounds like a way to firm up shifts, too?

Lastly, is there anything to get 'off the line' faster w/the 4EAT? Can programming affect the TC's stall speed or whatever gets the car moving?

I'm holding out on doing the 5-speed swap as long as possible!

Thanks,
Td

longassname · Post by **longassname** » Tue Dec 29, 2009 5:08 am

I am familiar with "the power mode mod" but have never been interested in it. The US model SVX switches to power mode when the throttle is pushed far and fast. The power mode mod lets you switch to power mode with a button. People with stock shift maps like it because anything is better than driving on the stock normal mode shift maps. Many of the people who have TCUs with my shift maps now had the power mode mod first. After getting my shift maps they invariably remove the power mode mod because they no longer need or want it.

Post by **Legacy777** » Tue Dec 29, 2009 6:48 pm

wtdash wrote:Lastly, is there anything to get 'off the line' faster w/the 4EAT? Can programming affect the TC's stall speed or whatever gets the car moving?

Best (fastest) way to get off the line with an automatic is to left foot brake. It may not be the nicest on the transmission, but it works.

Buffman · Post by **Buffman** » Tue Dec 29, 2009 8:43 pm

^^ or a well built high stall torque converter. I don't know subaru programming, but I've programmed many LT1s, and there's nothing programming wise to make a trans stall higher. foot brake it, or new TC.

Is there anything in the Programming to allow the Lockup to occur sooner? It seems on my 92 that lockup takes awhile to occur. I know 4th gear doesn't go until it reaches a certain temp, but it seems that lockup occurs way after that. I'd be interested in knowing if there was a constant value/switch to change to have lockup occur a lot faster. Winter driving is one thing (too cold and shudder will occur), but there's no reason, for spring/summer driving that TC lockup can't occur soon after 4th gear becomes available.

Matt

ericem · Post by **ericem** » Tue Dec 29, 2009 8:45 pm

Like I said I would really like my 4th gear to be always locked up, and for it to just jump to 3rd after 20%+ throttle.

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Transmission control unit upgrades/customization

Transmission control unit upgrades/customization