Power Mode Override Switch - Update

[svxistentialist]

Thanks for chiming in, Joe. Are you certain that the torque converter doesn't lock up when the TCU is in power mode? The reason I ask is that, from my understanding of the torque converter lockup control mechanism, it seems that the converter is always locked up in 2nd, 3rd, and 4th gear, no matter what. I believe the hydraulic circuits in the transmission are designed so that, in those gears, there is no oil pressure supplied to the lockup clutch.

Yes, pretty certain. There is an operation chart in the ATSG manual that explains it. Lock-up is most noticeable in D4.
Lock-up does not work in R,N or 1. It does not work below 40 degrees C, during shifting, at WOT or under rapid acceleration.
For steady driving it will lock in 2, 3 or 4, but only in Normal range.
The software makes the assumption that if Power map is activated, the driver wants all available torque for acceleration, and the TCU commands the lock-up release circuit open, duty ratio 5%.

This is backed up by what we have found in practise; the gearbox will not lock once Power mode is on.

Joe

[vrg3]

Hm. I'll have to reread the factory service manual section about that at some point. Thanks!

[svxistentialist]

Hm. I'll have to reread the factory service manual section about that at some point. Thanks!

The manuals are ambiguous, something I attribute to being translated from Japanese back along the line.

I've had US manuals WSM and currently Australia manuals, plus the ATSG one which is most useful.

A clue is in the no-lockup conditions definition: lock-up circuit is disengaged under rapid throttle change. This is the same circumstance as what activates the Power mode shift map when the Normal map is working.

The engineers want to give you as much acceleration as is available under fast throttle rise, so the torque converter is brought into play as a multiplier.

Just as a default situation, Power shift mode is designed to give you just exactly that; the ability to have as much torque as is available either to move quickly [acceleration] or pull up hills [heavy torque load]

So when Power mode is active, they presume you need torque, so the torque converter is kept in the loop, lock-up is disengaged.

Joe

[vrg3]

That does make sense. "Damn the efficiency, give me speed!"

[ericem]

Ok and techically when I do this the AWD should be running 50/50 to?

What should I ground it to anyway? Just find a screw somewhere I am thinking that is threaded to the chassis.

[svxistentialist]

Ok and techically when I do this the AWD should be running 50/50 to?

What should I ground it to anyway? Just find a screw somewhere I am thinking that is threaded to the chassis.

No to the first, yes to the second.

When you ground A4 you are then in full-time Power mode. This is no different from the Power mode you always had when you floored the boot.

Being an electronic gearbox it will still decide how much power to send to each axle based on the signals from the two speed sensors and the ABS computer. Whichever wheel is slipping will get less power, continuously variable depending on traction slippage. Not 50-50.

Use a good chassis ground anywhere you wish. If you bring the wire back to the shifter console, there are ground points there already, plus you can interrupt the wire with a switch and have the switch near to hand.

Joe

[Legacy777]

Very cool information guys. I'd definitely be playing with this if I still had my auto

[vrg3]

I believe you could tap pin 20 of that same connector for ground if you wanted.

But there's another idea that might be cool -- I think if you removed the contact from pin 6 (it looks like that would be a blue-with-yellow-stripe wire on Legacies) and put it into pin 4, you'd turn the Manual-mode switch into a Power-mode switch. From glancing at the wire diagram, I'd say that if you did that, then whenever you pressed the Manual button the TCU would go into Power mode and both the POWER and MANUAL lights would illuminate.

You'd lose Manual mode that way though.

[b3lha]

I believe you could tap pin 20 of that same connector for ground if you wanted.

But there's another idea that might be cool -- I think if you removed the contact from pin 6 (it looks like that would be a blue-with-yellow-stripe wire on Legacies) and put it into pin 4, you'd turn the Manual-mode switch into a Power-mode switch. From glancing at the wire diagram, I'd say that if you did that, then whenever you pressed the Manual button the TCU would go into Power mode and both the POWER and MANUAL lights would illuminate.

You'd lose Manual mode that way though.

Correct. You also lose the ability to run the TCU diagnostic check (because you have to click the manual button to do that).

[skid542]

Hmm.... that's an interesting thought Vikash.

I don't see why if you had to run diagnostics you couldn't just switch the pins back. I haven't tried to remove them before but it doesn't seem like it would be all that hard.

I do like the 'cleanliness' of the idea and would save me from having extra wires running around and extra switches.

[TheSubaruJunkie]

Where is the TCU located on our Turbo Sedans/Wagons?

[ericem]

If you look under the dask then look up and you will see a goldish box with 3 different connectors.

http://www.surrealmirage.com/subaru/swa ... l.html#tcu

[skid542]

Eric's right. The TCU is up under the dash on the left side (facing out the windshield). There are two 10mm nuts holding up there. It is much easier to mess with the wiring by taking the nuts off and dropping it out.

In order to get the pin out of the connector, there is a 'hinged' portion of the connector that clamps over the pins to help hold them in place. If you use a small set of pliers right over the the 'button' you press to get the connector out of the TCU and then pull back, you can expose the back side of the pins. From there I stuck a tiny screwdriver into the pin and pushed like hell until it popped out. There might be an easier, correct, way of removing the pin but my method did work with enough force and gentle words... Just be sure not to mess up the pin in the process.




Now as far as using the manual button to control the power mode - it works great. You get the manual mode light that comes on to let you know you have the switch activated which is very nice as grounding pin A4 doesn't lock the TCU into power mode - just makes it more sensitive.

My initial observations taking the car out is that it will drop into power mode very easily. It takes much less of a throttle position differential than without the pin grounded. However, once in mode it responds the same including the time it takes for it to drop out if you lift your foot off the gas. It does 'seem' to make a little difference in the behavior of the tranny when it is not in power mode in that it seems a little more responsive and tighter shifts. This mod definately adds to the driving experience and reduces the time lag between giving it gas and feeling the car accelerate. This is particularly nice while driving the twisties.

However, since it does drop out of power mode, if you really have to slow down for a tight turn, don't expect the power to be right there. If you lift your foot off the gas it will allow the engine to drop back down to idle. Power mode does not equal 5sp driving characteristics. Placing the gear selector in a particular gear is the only way to maintain engine RPM and effective engine braking while slowing down.

While I've very pleased with this mod, it still doesn't give me the driving control that I was hoping for. Maybe a true gear selector would, but even using the gear selector in 1-2-3 still doesn't match the 5sp experience and control. You can't slip the tranny mid corner to be ready in the power band for the exit which becomes important when you're driving in a spirited but not all-out manner.

Thanks again though to B3lha for this easy power mode control. It does make the car much more fun to drive.

[Legacy777]

Here's a pic of the ECU & TCU
http://www.main.experiencetherave.com/s ... cuhide.jpg

[b3lha]

However, since it does drop out of power mode, if you really have to slow down for a tight turn, don't expect the power to be right there.

When you say "it does drop out of power mode", do you mean the power mode light turns off after a while and the shifting goes back to normal? It shouldn't do either of those things.

If you lift your foot off the gas it will allow the engine to drop back down to idle. Power mode does not equal 5sp driving characteristics. Placing the gear selector in a particular gear is the only way to maintain engine RPM and effective engine braking while slowing down.

Yes. It's still an auto, but it has a sportier shift map. I find the best combination for spirited driving is to keep the stick in 3 and the power mode switch on. See what works best for you. I assume our 3.3 has more low-down torque than a 2.0 turbo. Therefore, it's not as important for us to maintain rpm as it is for you guys.

Thanks again though to B3lha for this easy power mode control. It does make the car much more fun to drive.

You're welcome. Equal credit goes to Svxistentialist and Nomake Wan for their part in figuring this out.

[skid542]

When I say it drops out of power mode I mean the power light turns off and it upshifts if I'm not hard on the throttle. It comes back easier, but mine still drops out.

James - does yours drop out as well? I wonder if it's something that's a result of using the manual mode button?

I'll have to try putting the selector in position 3 and see how that works. I'm sure you have more low end torque with the 6cyl, but just for reference sake us USDM guys got the 2.2.


Then a big thanks is also due to Svxistentialist and Nomake Wan.

[TheSubaruJunkie]

This maybe a stupid question, but I though I would ask anyhow.

What I'd like to do, is have a push button switch control the ground on the TCU. However, I want it to also control a small LED so I can be aware wether or not the power mode is in over ride or not...

Im thinking in order to do this, I can supply the 12v to the LED... and run the ground for the LED through the same switch on the same terminal that I would wire Pin4 on the TCU to... and when the switch is engaged it would ground the LED illuminating it, and set the TCU in Power Mode.

Would this have any ill effects on my TCU at all doing this with the LED involved?

-Brian

[Legacy777]

No I don't think that will work, you'll be feeding 12v to that pin of the TCU.

You could use relay to do what you want to do. There may be another way, but I know using a relay would work.

[TheSubaruJunkie]

Thats what I thought. Didnt know if the 12V would effect things or if it would just act as another ground.

I thought about using a relay to control the LED but thats a bulky sollution. Maybe i'll just keep searching for a DPST push button on-off switch.

-Brian

[93Subadan]

I'm no sparky, but...

What about using a diode in line with the TCU? It would prevent 12V from going to the pin and when the switch is flicked both would go to ground. It might be worth testing it on a benchtop...if only I had some free time

https://webfiles.colorado.edu/taylorbr/IMG.jpg

[skid542]

I would think that there would be enough voltage to run a small 12v lamp inline between the TCU and ground. Until you flip the switch you won't have any current flowing through it, but of course once you flip the switch you should be able to flow enough to light a tiny lamp. Your relay is going to flow about as much current as a tiny indicator.

Do they make 12v LED's yet?

I personally think you're making this too complicated (I know I'm not one to comment about that... ).

[TheSubaruJunkie]

Yeah i have a few 12v LED's I picked up for another project.

And I like things complicated

The Diode trick might work. However, I didnt know voltage flowed through the TCU pin. I'll have to test that.

-Brian

[skid542]

The only way you can 'ground' a pin is by connecting one location that has a voltage potential to a ground. The amount of current flowing through may be negligable, but once you put something in line to make use of the voltage potential, current will flow. The only question is what voltage do you have at the TCU pin, I'd guess either 5v or 12v.

My pin is connected to my manual button, not knowing the wiring off hand, there is either enough power available to light up the manual light on the dash gauge or trigger the relay that operates the manual light. This should be more than enough for a little LED.

Just put in line and run with it .

[TheSubaruJunkie]

I'll take my multimeter home with me and test its current.

[b3lha]

Don't you have a power light on the dash?

You could use a double throw switch. One side of it switches the TCU pin to ground, the other side switches the lamp to ground.