An idea for AT...

[Nomake Wan]

As I was driving around my lovely back-road today, messing with gear settings, I became somewhat annoyed at the fact that near 6500 RPM in second gear (with Manual on), if I let up it would upshift. If I dropped the speed back down and got on it she would downshift back into second, but it was annoying having to do that.

So I thought to myself, "This transmission's electronically controlled. I wonder if there's a way to prevent that from happening." The most fun I've had in my car so far has been using the numbered gear select in manual mode. Rev-matching, my own shifting... it's still not a manual transmission, but it makes me feel a little more in control. Except when it upshifts of its own accord from second to third.

So, is it possible to trick the TCU into not upshifting? If there's a way to change the TPS signal, I could wire that into the manual switch so that it's only changed while the Manual setting is on, thus not affecting normal Drive conditions. I don't want to get rid of that, since this car's my daily driver... but to be able to turn off the automatic upshifting would make my setup perfect for me.

So, gurus. Is there any feasible way to go about changing the TCU's mind?

[vrg3]

Why not just use the gear selector? Put it in '2' and it won't upshift out of 2nd unless it absolutely has to.

[Nomake Wan]

No, that's just it. I've been using the gear selector, that's why I've had so much fun lately. But when it's in '2' it upshifts into 3rd if I let off of the gas at high RPMs. Since I often adjust my speed by just removing throttle, having it upshift into third isn't desirable. Especially if I'm about to enter a turn, and the action of upshifting throws off my car's balance with its jerky transition.

So I'm actually asking about the gear selector. I'm asking if there's any way to prevent the TCU from shifting into third when using the '2' select in Manual mode. 1st doesn't upshift (though sometimes the lever sticks in first and won't go up to second, have yet to figure that one out), and I've never pushed third hard enough to where I could find out if it upshifts. So all I'm concerned about is second.

[vrg3]

Oh, I didn't realize you were already in '2.'

That's odd... it shouldn't upshift into 3rd unless it has to in order to prevent exceeding the redline.

Hm, I wonder if when you let off the gas the engine speed momentarily rises minutely for some reason, and that causes the upshift.

What you're asking about is eliminating the rev limiter built into the TCU. In principle this seems like it should be pretty straightforward. The TCU gets its tach signal from the ECU, right? You could make some kind of signal conditioner that goes in that line. It would pass the signal through unchanged until some threshold speed (like maybe 6400 RPM), and then output a signal representing that threshold speed. So the TCU would think engine speed never exceeds the threshold.

Kind of like what you'd do to defeat a speed limiter, except a little more complicated because it's fairly important that the signal be correct most of the time.

You'd then be relying on the ECU's fuel cut at 6500 RPM to make sure you don't overrev.

Hmm. An LM2907 chip set up to trigger some kind of SPDT analog switch, and a 555 timer to generate the false 6400 RPM signal... That could do it.

Or maybe a simple voltage follower with a low-pass filter and a Schmitt trigger... You could build that with a single chip, three resistors, a capacitor, and a potentiometer.

[Nomake Wan]

I have only moderate experience with any kind of "advanced" electronics (the surround system I'm building currently is about the limit of what I can design and build on my own, without help)... any chance you could e-mail or PM specifications for what you're describing? I understand what it does and how it does it, but implementing that is beyond me at this point.

But I never thought of simply making it relay the same speed at that RPM... that's good.

[vrg3]

I mean something like this:

http://www.graphics.cornell.edu/~v/pics/freqlimiter.png

The 0.1uF and 50K values I just kind of pulled out of the air... They'll probably work out but you'd have to tune the variable resistor carefully.

You'd have to test this circuit either with a signal generator and an oscilloscope or by installing it on the car and using a Select Monitor to view the TCU's RPM readings.

[Nomake Wan]

A little added background:

I found this post by ciper in a thread which relates to what I'm experiencing:

Im sure this is correct. In second gear you cannot shift back to first no matter what throttle position you have if you are already over 25mph. Under 25mph will shift you back into first.

This is exactly what happens in third when the manual button is enabled. Once you hit 25mph in third you can do whatever you like and the car will stay in third. If you have the throttle floored while still in second you can hold it to redline, if you release it slightly at any time though you will go into third.

When I'm doing 'manual' shifting, I always have the manual button enabled. I start in the '1' setting, rev to redline, then shift to 2nd... and if I've got enough space (read: on back-road) I rev to red-line and shift to third. This way, I don't experience the strange 25-mph shift pattern mentioned (since I don't get down to 25mph in third). However, as he mentioned, I do experience the shift when I release slightly in second and it upshifts into third. This is the only shift that has actually affected me, which is why I'm targetting it so specifically. The "fix" only needs to work while in second and the Manual button is depressed.

[BAC5.2]

Does it upshift to 2nd when you aproach redline in 1st and let off?

[Nomake Wan]

Not that I've noticed. However, to be fair, I usually never find myself letting off at redline in first, since I hop out of that gear rather quickly. And when I downshift rev-match back into first, it doesn't jerkily try to stay in second, so again, not that I've noticed.

EDIT: Tomorrow's Friday, so I guess I could go driving and screw around in first to try to see if it does the same thing. Third, though, would be a bit tricky. I don't think I have enough room to see if third'll upshift into fourth. Besides, I'm not really sure where third redlines... I would guess about 100-something MPH. But like I said, I don't have enough room to go anywhere above 100 for more than a second or two where I do my test-driving.

[THAWA]

There's something screwy with your trans/tcu. The tcu will only shift into 3rd gear with the selector in 2 when you hit 6500 rpms. Either something is sending some incorrect signal or maybe you're thinking it's 3rd gear when it's really something else. I can't remember if the torque converter will lock/unlock in 2/2nd gear. The TCU also will not shift to the next highest gear from the selector you are in if you let off at redline. It'll just engine brake down. The problem is not in the TCU, the problem is in the driver. You're not making much if any more power at 6500 rpms than you would be at 5000 or so. It may be less actually. Bring the rpms down and you wont have the tcu shifting when it hits 6500. Having the manual button on isn't always the best idea. It doesn't do what you think it does. Third relines at around 113.

[Nomake Wan]

Well, I'll try driving around with and without the button on and see if there's any noticeable difference. If not, I guess there's no reason to have it on.

Again, I'll do more test driving and really work out exactly what's going on. I don't doubt your comment about the driver; I only just started messing around with this stuff.

Thanks for the info on 3rd's redline. No wonder I never got it there.

[tris91ricer]

Nomake- Do a search for some of Cipher's threads, and he explains how the cruise control alters the shift map for the TCU. It was something about getting to 100 in like 5-6 seconds, but having the cruise on made a difference, when the manual button was engaged. But YOU have to shift it, i think.
Meh, I'll search, too, since I'm a little unclear about it. It's been a while since I've read it.

[Legacy777]

Just some clarification.

The manual button is NOT needed, it is not helping you in any what way what-so-ever in manually shifting the car.

Just put the gear selector in the spot it needs to be in and drive.

When I had an auto, I'd drive around with it in the 2 position when I wanted to drive agressively in the twisties. The TCU will SHIFT at the 6500 redline.

I have once or twice revved the engine fast enough in first gear where I hit the ECU's rpm limiter, and it cut ignition....not fuel.

[tris91ricer]

Okay, josh, I tried searching for Cipher's little shift method (which was a link to the body and chassis forum) but it was where he was touting being able to get to 100+ mph in the fastest time possible, using the cruise control to alter the shift map. Do you remember what I'm talking about? It seems that the thread I'm referencing either has been deleted, or I'm just imagining it, which, I don't think is entirely out of the question..
Little help?

[vrg3]

If you were searching for posts by Cipher, that would hinder you. His username is ciper.

I think this is the thread you're talking about: http://bbs.legacycentral.org/viewtopic.php?t=1468

[THAWA]

He actually drives like that too. It's cool watching him drive. He's very smooth too.

[Nomake Wan]

Ah, that's an awesome idea! Another thing I'll need to try out (that is, if I get enough room. I tried starting further up the road, but ended up bouncing my car way too much to accelerate).

Okay, I went driving hard for about an hour or so today, and tested as much as I could.

First off, you're all absolutely right. I saw no difference between my shifting pattern with and without the manual button on. So I'll leave it off, now (I've only launched in first so far).

Also, to whoever asked, the TCU does indeed upshift on its own when hitting redline in first. In fact, on a whim, I just kept accelerating, and it upshifted into third while still in the '1' position. It resulted in my having to carefully slow down so that my car didn't jerk heavily on the downshifts. I guess I just didn't notice the upshift because I shift into second just before redline hits.

Yeah, I thought it was weird hearing 'fuel cut' on a rev limiter... I was sure it was an ignition cut. Now that's confirmed, cool!

So it looks like what I'm going to want is something exactly like what you suggested, Vikash: a circuit that cuts in at 6400RPM and sends a constant 6400RPM signal. The only problem I see with that is if I'm ever in Drive and mash the pedal, going into Power mode... it'd shift to first, redline... redline... ignition cut...

So basically, I would need a circuit that only works when enabled remotely, like by switch (or like I mentioned earlier, by wiring it into the "useless" Manual button, which would then have a more literal use).

Okay!

[angus106]

i love just mashing the throttle in first and getting it to jumpt to third at redline... i'm still learning alot about these cars, my neighbour teaches me new stuff all the time (subaru mechanic). he told me about that shifting thing... i've found that when i launch like that the car accelarates super hard.... my neighbour said it'll shift up like that to avoid damaging the motor... but if you leave the gear slector in first and let of the gas the car will engine brake but it will not downshift to second but to first..... he does it all the time to scare passengers in his car his trannay is doing just fine... (just did a fluid change and there were not metal shaved surprises to be found).

thought i'd share what i've learned don't know if it really gets u any further ahead but meh.

angus

[Nomake Wan]

Yeah, that's why I had to be careful about slowing in first. But that's interesting; I'll have to try that sometime when I've got my friends in the car. XD

Engine braking's a hell of a thing.

[tris91ricer]

Thanks Vikash, that's what I was looking for! Now, I just need a way to bookmark all these different threads..