ECU tune Transmission control unit?

[svxfiles]

Originally Posted by oab_au

Oh come on Tom,
Every one knows thats not you.







Harvey.

TEE,HEE,HEE,HEE,HEE, snort!

[newsvx]

Tom,
Where do I sign up for your NEXT class??

Harry

[svxfiles]

Originally Posted by newsvx

Tom,
Where do I sign up for your NEXT class??

Harry

The next class will be held in PA.
Third weekend of May.
It will be an exploritory of gas expansion in an uncontrolled manner.
Or, just outside the Manor in the ,,,,,
parking lot!
Some kids never change!

[longassname]

LOL, good video. Not to take the video seriously....but I was just explaining it in an email so I figured I'd copy and paste the explanation over here. It's important. At this point the newest possible automatic transmisison that can be swapped into an SVX is 13 years old so it's bordering on rediculous to do these swaps already and only getting more so with each day. People should understand that SVX transmission failures can easily be prevented with a simple plug in that anyone can do, even without any mechanical ability.

On the SVX, the performance TCU firmware now includes modified line pressure control maps for 3rd and 4th gear. There are individual line pressure control maps for each gear but in the stock programming Subaru used the same map for all 4 gears. It works fine for 1st and 2nd which use much, much larger clutch packs than 3rd and 4th but the line pressure is marginal to not good enough to hold the little high clutch under light cruise. This results in the transmission equivalent of driving with your brakes on, continuously wearing the high clutch and brake band and making huge amounts of heat. The stock programming results in about 65 lbs of line pressure at light cruise; I change it to close to the max pressure resulting in about 150 lbs of line pressure. This change is the fix for the transmission failures that plague all SVXs; for this reason, a performance TCU is a necessity for any SVX.

[Huskymaniac]

I posted a hypothesis in the tranny failure poll thread but figured I would re-post it here since it is relevant:

Mike's new TCU code keeps the line pressure high at low throttle with the belief that this will help avoid tranny failures. Clearly, the modifications/upgrades made by Subaru between 1992 and 1995 reduced the failure rate. These Subaru modifications were to address the known flaws with ATF flow and clutch material.

I think, together, the original TCU programming and original tranny flaws were a really bad combination. When someone is stopped or cruising at light throttle, the line pressure is low due to the original TCU programming, as Mike has pointed out. If one then stomps on the gas, the engine soon delivers a ton of torque to the tranny. If that torque arrives before the line pressure rises in response to the TCU asking for more line pressure, the weak clutch material, high torque and low line pressure would result in a slip which would damage the tranny. If done many times, the tranny starts slipping worse and worse and the ATF heats up more and more and you have a downward spiral.

The poor ATF flow may be one reason why the line pressure would rise slowly when the TCU signals for higher pressure. This could be the main cause of or, at least, add to the delay. Just a theory. But, if true, Mike's TCU changes plus his valve body modifications would both be a big help in addition to what Subaru already did in the later models. Unfortunately, there still isn't a TCU upgrade for those of us with 1996 or 1997 models. I still plan to order one from Mike but if anyone with an OBD2 model year is also interested, perhaps we could order the upgrade at the same time to split Mike's development cost.

[longassname]

Subaru really just played around with the high clutch hub trying to improve the cooling of the high clutch. There were several different versions and I see them all with no discernable difference in failure rate. If your poll is showing less transmission failures in later model SVXs I would strongly suspect that is soley do to there being less later model SVXs.

The really early SVX transmissions had a different high clutch drum and smaller reverse frictions. In those transmissions I do see a higher incidence of reverse clutch failure on top of a failed high clutch. This is clearly caused by the failed high clutch though so I wouldn't even worry about having one of those transmissions.

[James Scott]

So... Since I apparently have a swapped (used, but apparently rebuilt) '92 AT in my '95 SVX AWD L Blue.. . I am looking forward to a sooner failure, than average.. for SVXers.. RiGhT.. ??

Thanks

P.S. Hopefully, the Ecutune TCU (waiting for installation).. will help prevent its early demise!

[James Scott]

I like the way my SVX drives now with the TCU MOD and 1av1 upgrade.

However.. . .

Am I getting even more senile than I was aware? .. It seems there are 4 shifts now.. (5 spd AT) .. compared to the previously noted 3 shifts (between 4 gears).. .

Please HeLp! .. .

Thanks..

P.S. WhAtAmOd!

P.P.S. Overdrive.. ??

[NeedForSpeed]

Originally Posted by James Scott

I like the way my SVX drives now with the TCU MOD and 1av1 upgrade.

However.. . .

Am I getting even more senile than I was aware? .. It seems there are 4 shifts now.. (5 spd AT) .. compared to the previously noted 3 shifts (between 4 gears).. .

Please HeLp! .. .

Thanks..

P.S. WhAtAmOd!

P.P.S. Overdrive.. ??

Well, the car shifts to 2nd, 3rd, 4th, then TC lock
You could count that as four shifts

[James Scott]

Wat is TC Lock? Like OD?

Wish I understood.. Hmmm?

[NeedForSpeed]

Originally Posted by James Scott

Wat is TC Lock? Like OD?

Wish I understood.. Hmmm?

Jim,

The transmission is a 4EAT, four speed electronic automatic transmission. The gear ratios are 2.785, 1.545, 1.0, 0.694. Fourth gear, less than 1.0, is an "overdrive" gear. It could be said that the SVX has a three speed with an overdrive 4th gear.

You also have a locking 'TC' torque converter. The Subaru 4EAT is programmed to lock the torque converter in fourth gear. When the torque converter locks, the rpm will drop about 200 rpm. You can feel the lock, and you can see the rpm drop on the tach. It feels like a shift

[James Scott]

The transmission is a 4EAT, four speed electronic automatic transmission. The gear ratios are 2.785, 1.545, 1.0, 0.694. Fourth gear, less than 1.0, is an "overdrive" gear. It could be said that the SVX has a three speed with an overdrive 4th gear.

You also have a locking 'TC' torque converter. The Subaru 4EAT is programmed to lock the torque converter in fourth gear. When the torque converter locks, the rpm will drop about 200 rpm. You can feel the lock, and you can see the rpm drop on the tach. It feels like a shift

Sure enuf! That's IT! .. Thanks.

By the way.. You mentioned "electronic" 4EAT.. I've been trying to adjust the Inhibitor Switch and shift linkage.. Never cud make it work right since used/rebuilt AT installed.. Just ordered Inhibitor Switch cuz it dint have continuity in N, D and sorta not in 1st!

Is this AT controlled (shift, or lock into gear) by the electrical inhibitor switch info... or does the inhibitor switch just (1) allow start in N [mine doesn't now] and P .. and (2) switches gear position indicator lights on dash mainly?

Isn't the shift a mechanically controlled event, without intervention from the inhibitor switch?

Thanks for your thorough explanation..

[longassname]

I have several front wheel drive TCUs in stock and socketed. If I sit down and make the performance fwd tcu firmware are there a couple people who immediately want fwd TCUs?

[Huskymaniac]

Originally Posted by longassname

The 96 TCU I did was labled MQ and is under the steering column. It uses the same processor as the obd1 cars and I have done the ECUtune performance mods to it, given the firmware to Phil, and posted the code for the ECUtune mods to Phil's gearshift map thread.

The TCU I have as a 97 is the same as your MY. So I guess there is a break somewhere in 96. The MY uses a different processor and does not have an external memory socket.

Mike,

I got a little mixed up in ECU/TCU land. I know you don't have an OBD2 ECU available but it sounds like a 1996 TCU may still be upgraded IF it is labeled MQ versus MY. Is that correct? If so, do you have any idea if an MY TCU can be replaced by an MQ in a 1996? After reading lots of threads on ECUs and TCUs I got the impression that all bets are off for any ECU/TCU mods in an OBD2 car but, after re-reading this thread, I am starting to think that may not be the case. And I found another thread from last November where you said that you found the solenoid A memory locations for the 1996 TCU. I need to look at my car to see what the code is on the TCU and, hopefully it will be MQ.

[longassname]

Correct, I can and have done MQ TCUs. I do not know if you can replace an MY with an MQ. I've been told the cars with MY TCUs have more wires in the plugs but only by one source with no independent verification. I do know the MY TCU is much smaller and mounts differently so even if were electrically interchangeable it probably wouldn't be easy to do.

So to make it very clear: If you have a 96 with an MQ TCU I can do it.