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Guest Message by DevFuse

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4eat at 4200 or so rpm, what happens?

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43 replies to this topic

#26 Guest_CipeR_*

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Posted 10 May 2002 - 02:52 PM

I will try to write down any numbers from my TCU so that we can perhaps start a list of changes made.

As most of you know the 4eat has been used in every car from 89 until present with only minor changes. The real differences come in the TCU. It could very well be that everything we have posted is true even though they are contradictary to each other.

#27 Guest_Legacy777_*

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Posted 10 May 2002 - 03:34 PM

I've tried it back in the day. It shifts at 40 mph from first to second.....like it always does.......unless mine is different because it's FWD....which I sorta doubt.....

I'll have to scour through those damn FSM's and try and find that info I was tellin you about.

#28 Guest_blackmxz_*

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Posted 10 May 2002 - 06:21 PM

ok i just went out and tried it on the 90 and it did not start in second when in D but the 93 does so there must have been a change in the tcu

#29 Guest_Legacy777_*

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Posted 10 May 2002 - 06:32 PM

ok.....that would make sense......

#30 Guest_CipeR_*

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Posted 10 May 2002 - 08:20 PM

Darnit, I had printed out that wire diagram that you (legacy777) had linked to and I lost it. I searched the board for that post and I cant find it..

I need that wire diagram to test this weekend! I hope your still around.

edit: found it!

#31 Guest_subyroo_*

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Posted 11 May 2002 - 04:50 AM

CipeR just get a REAL Subaru.

The type where YOU dictate the gear changes, not the cars computer or auto box.

:lol: :lol: :lol: :lol:

#32 Guest_CipeR_*

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Posted 13 May 2002 - 09:22 PM

So I just wrote about a 15 paragraph message with all sorts of usefull data to any of you and the fu(king java bulloney that I clicked on to get a description of the ezcodes ( i knew I should have just used < b > ) froze the damn window......

Anyways Im lazy to rewrite all of it right now but I found some very interested info.

Including what might be a 70cent shift kit!!!! I just ordered the parts from an online electronics retailer.

I also was able to see that the torque convertor "can" lock in 2 3 or 4/D but more often than not you will only see it in 3 or d since by the time the circumstances are met to lock it you have shifted. Realize that the torque convertor is not a simple on off operation. It slowly applies the clutch exactly as if you were in a manual transmission vehicle.

Also realize that line pressure is DIRECTLY effected by throttle position and NOT rpm.

On top of that the voltage required for a very stiff shift is about .8 while a very soft is about 1.6 . Line pressure is controlled by a solenoid that acts as a bleeder valve, the higher the voltage the more fluid bypasses. If you were to take the tranny resistor out and connect it directly you would run the solenoid at a variable 10-12 volts. More than likely it wouldnt damage the solenoid (at least right away) but you would get virtually ZERO pressure!

Also any of you driving around without a resistor connected may want to stick it back in for the moment. I have some information that could get you to keep it connected permanently. I will need the help from some of you who may understand the function of the tranny better than I.

Hehe, I was able to lock the differential into what was probably a 50-50 front rear split as well :)

having a good mulitmeter with memory and such makes this very easy.

#33 Guest_blackmxz_*

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Posted 13 May 2002 - 11:05 PM

so your tranny locked the convertor in 2nd and 3rd? very strange, our 90 is driven in 3rd all the time since the cluitch on the convertor failed (slips badly) and has never locked in 3rd nor my 93 which i use 3rd alot also. what year is yours again? for the seemingly unchanged 4eat their sure seems to be alot of changes in the way the tcu operated through the years.
so how did you end up locking the center diff to a 50/50 split? was it the brown wire like i have my switch hooked to? found out today my switch in the brown wire will also engage the awd with the fwd fuse in, some i will have to remember when i tow the car!
im am intrested to hear more about your results.

#34 Guest_Legacy777_*

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Posted 16 May 2002 - 10:18 AM

ciper.....what info you got about the tranny resistor and such......keep us posted.

Russ.....can you make this a sticky?

#35 Guest_PaganQWA_*

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Posted 17 May 2002 - 08:10 PM

blackmxz: I'm able to lock the torque converter in 2, 3 and 4 in my '90 Legacy L (FWD) Maybe your just not noticing it? Its a pretty subtle change in RPMs usally.

#36 Guest_blackmxz_*

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Posted 17 May 2002 - 08:58 PM

nope i know for a fact my 90 fwd and 93 awd do not lock in anything but 4th, i do alot of highway driving fom wi to wy in 3rd and 4th and its never locked in 3rd under any circumstances, i dont drive our 95 enough to know if it is the same or not. the 90 had the clucth go out on the convertor so its been driven in 3rd (so the convertor wont lock) for months now and has never locked, and id definatly know it if it did (clutch slips and makes alot of noise when it locks) i pay more attention to my tach than i do the speedo and would most def know if it did lock.

#37 Guest_SmashPDX_*

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Posted 17 May 2002 - 11:56 PM


Consider it stuck :)

#38 Guest_Herarety_*

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Posted 26 May 2002 - 03:55 PM

4eat huh?

My Probe GT has the same. Interesting, as it's a Mazda drivetrain.

#39 Guest_Legacy777_*

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Posted 27 May 2002 - 08:28 PM

yeah.......4eat is used in a lot of japanese cars.

Oh and here is a blurb ciper wrote up......

Anyways so Ive been a little lazy lately. Im planning to do a write up on the resistor. The data I have should be applicable to all 4eat owners since they all seem to use the same 10 ohm 25 watt sandbar resistor.

So far Im running my car with a 15 ohm 50 watt unit. I will compare this to a 19 ohm unit soon.

My basic finding has been that the bypass valve needs to be open quite a bit when stopped. Removing the resistor does not allow this to happen, and most likely will eventually damage the tranny. With too low a voltage at stopping speed or with the resistor removed the tranny does make a funny buzzing sound. Its very faint so most problably dont notice.

Going from the 10 ohm to the 15 ohm dropped the stop voltage from about 3 volts to just about 2 volts. With this in mind anything over 20 ohms would seem to put you right back at too low of a stopped voltage.

The great thing about this hack is that at low throttle the shifts are still in the soft range. Its up at higher throttles that you can really tell the difference.

The TCU outputs a variable voltage based on a number of factors including the TPS and at what point of the shift sequence it is in. Usually this voltage ranges from about 9 volts at full throttle in first gear to 12.5 volts at a full stop. This voltage is directly dumped through the resistor then back onto the line that contols the bypass valve.

The bypass valve never receives voltage under .8 volts unless its for a breif second when the throttle is mashed. Running at voltages lower than 1 volt all the time causes some weird behaviour. This can include some bad shifts and certain clutches not engaging when they should.

If you plan to try this yourself Id suggest grabbing two 25 watt units of the same spec and runing them parralel. Use the aliminum body with heatsink type so they are easy to mount and you dont burn yourself. 5% models should be fine.

I haven't played with it yet. Still messing with other things

Unplugging the resistor is a bad idea. Some of the reasons I do not have enough knowledge to explain why.

A few like I mentioned above, running at full pressure even at a stop, jerking and engine breaking not functioning in the correct gears. I also dont like the idea of buzzing when coming to a stop, as the bypass is fully closed.

One that someone could help me with to use correct terminology.

For example you know when you are in a gear it will lock the first planet ring then lock the outside planet gear to the wheels and the sun gear to the other planetary set. When shifting from 2nd to 3 it has to unlock and lock 4 different items if I remember right, Ill check the information I have.

The TCU will be tuned for these events to happen in the correct order based on the amount of "lag" each operation has. When increasing the line pressure to maximum you could have a time when you are supposed to be upshifting but the current combination is a lower gear ratio than the previous gear. Does that make sense?

Besides that Im still trying to study exactly what happens to the TCU. Running too high of a line pressure at the wrong times by either too low a voltage or no voltage input from the resistor dropping line for too long seems to make the transmission to either go into "stupid" mode or learn to try and work around the shifts. The shifts start to get more unpredictable in the feel, where it seems to kinda do a double clunk into gear.

Either way Ill post my findings after try a few more values to replace the resistor. So far it seems that my current 17 ohm version is a pretty good balance

#40 who1981


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Posted 13 October 2004 - 09:08 AM

Very interesting... I'll have to play around with some of these power resistors I have laying about.

I have heard about a "Shift Kit" device, mostly for SVXs, that, depending on throttle (via Vacuum switch), disconnects the Dropping Resistor...so when the throttle is pressed to about 1/3, the switch opens and disconnects the resistor.

I wonder if a hybrid of the two methods would be best...a throttle activated switch that would put a, say, 15ohm resistor in series with the stock 10ohm? Or maybe replace the stock resistor with a higher value, and when the throttle is closed, switch a resistor in parrallel... (Like a 20ohm stock, and a 20ohm switched)

Or get really fancy and rig some kind of solid state voltage control, perhaps with some sort of FET, perhaps controlled by the TPS itself.

Oh here is the site:

(Oh, one question though: Where is the resistor on a 97 Impreza 4EAT?):confused:

#41 oddcomp


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Posted 13 October 2004 - 09:38 AM

if you really want to do a programmable shift point setup for
electronically controlly auto box maybe look into this as a option?


#42 nncoolg


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Posted 30 October 2011 - 03:20 AM

has anyone done anything with the 4EAT and megashift?

#43 WoodsWagon


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Posted 30 October 2011 - 11:53 PM

They've done better actually. The 4EAT TCU has been cracked and you can do anything you want to it including paddle shifters: http://www.ultimates...ad.php?t=110222
Here's some other info on the same TCU: http://www.alcyone.o...tcureverse.html

Edited by WoodsWagon, 30 October 2011 - 11:56 PM.

#44 nncoolg


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Posted 31 October 2011 - 02:17 AM

We just need somebody to decode all that hex into shift maps and soleniod operation information and then it would be very usable for megashift.

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