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Registered
1992 SVX
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21 Posts
Discussion Starter #1
I'm visiting from the SVX forums and I thought I would share a little discovery we made in the hope it will be useful to you guys.

I've never seen an USDM Impreza, so I'm making an assumption that some of you have the 4EAT automatic gearbox and that it is similar to the one fitted to USDM model SVXes.

The USDM 4EAT has a power mode that comes on when you kick down on the gas. The power mode causes the gears to shift at a higher RPM for increased acceleration when overtaking.

The JDM 4EAT in my cars also has a power mode, but it is activated by a switch. I traced the wiring and found that the switch connects pin A4 of the TCU to ground. That's the 4th pin of the 1st connector.

After I posted that on the SVX forums, a guy called Nomake Wan compared the wiring on his USDM car and found pin A4 was not connected. So he grounded it to see what would happen. When he put shifter in D, the power mode came on, just like the Japanese cars.:cool:

Since then, a lot of USDM SVX owners have started connecting up switches to enable power mode and the feedback has been overwhelmingly positive. It makes the car feel much more responsive and sporty to drive.

A few guys on the Legacy forums also tried it, but with mixed results. It works for some but not for others. It depends on the firmware version of the TCU.

Maybe it will work for you, maybe not. But it is probably worth trying.
 

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Meany Head
2000 RSC
Joined
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10,235 Posts
There are not alot of 4EATs in here, but there sure are some. Would be interesting to to find out if this works. I wonder if my Wifes 04FXT has this mysterious Power Mode... Time to start digging through the FSMs.
 

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Premium Member
MY98 2.5RS Coupe Brilliant Red
Joined
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880 Posts
I'll give it a look and see what I can find after dropping the motor in tonight/tomorrow.

Any idea how to make a home grown Level10 shifter? Basically, a switch bank that allows me to lock the 4EAT in a gear and not have it downshift when the gas is mashed? I'm hoping to figure that one out before I send the car to the dyno so the guy can just stomp in 3rd and not worry about the car randomly dropping down to 2nd.

Nice find on the pin/switch combination.
 

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Registered
2000, Impreza, 2.5 RS,
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139 Posts
I have a 4EAT:bitehard: and noticed a long time ago the differences in gearing. Flooring it conservatively gets you slow/normal acceleration while slamming the pedal gets really aggressive acceleration. With a rebuilt transmission, heads and brand new stock full exhaust on my 2000 2.5 I get consistent 0-60 of ~7 seconds with no 4000k rpm launch. There is some PDF on the net from Subaru about the 4EAT, I read it a while ago and it mentioned that the gears are longer or shorter in response to ones pedal aggressiveness.
 

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Registered
1992 SVX
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21 Posts
Discussion Starter #6
Any idea how to make a home grown Level10 shifter? Basically, a switch bank that allows me to lock the 4EAT in a gear and not have it downshift when the gas is mashed? I'm hoping to figure that one out before I send the car to the dyno so the guy can just stomp in 3rd and not worry about the car randomly dropping down to 2nd.
The shifting is controlled by two solenoids. The electrical way to do it would be to force the solenoids on or off in the right combination for the gear you want. The four possible combinations (off-off, off-on, on-off, on-on) represent the four gears, but not necessarily in that order. You can force them on or off by disconnecting them from the TCU and tieing them to 5v or Ground as appropriate. That brute force method doesn't really appeal to me for a number of reasons including the tendancy of Subaru 4EATs to self-destruct.

My preferred method would be to modify the shift maps in the TCU firmware to hold the selected gear if the "manual" button is pressed. I have decoded the TCU and made some experimental modifications. But I haven't got as far as figuring out how to change the shift maps properly.

Phil.
 

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Premium Member
MY98 2.5RS Coupe Brilliant Red
Joined
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880 Posts
4EATs self-destructing from the brute force method? Haven't heard of it, but then again, I havne't read too many modifications to control the solenoids either. Both probably go hand in hand.

Is the TCU memory flashable like the latest ECUs? Having something built in to the controls that would hold it in gear if selected with the transmission selector would be a huge improvement.

At the very least, I'll look into the pin issue on my MY98 once it is out of the garage under its own power.
 

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Registered
1992 SVX
Joined
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21 Posts
Discussion Starter #8
4EATs self-destructing from the brute force method? Haven't heard of it, but then again, I havne't read too many modifications to control the solenoids either. Both probably go hand in hand.
SVX 4EATs tend burn up their clutches every 50K miles or so, even in normal operation. Any modification that might speed up the process needs to be thought through very carefully.
Is the TCU memory flashable like the latest ECUs?
On my car, it's a case of unsoldering the ROM chip and soldering a new one in it's place. Maybe the newer ones are flashable.

Let me know how you get on with the pin A4 trick.
 

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Registered
2003 Subaru Forester Black/Gra
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583 Posts
I'm visiting from the SVX forums and I thought I would share a little discovery we made in the hope it will be useful to you guys.

I've never seen an USDM Impreza, so I'm making an assumption that some of you have the 4EAT automatic gearbox and that it is similar to the one fitted to USDM model SVXes.

The USDM 4EAT has a power mode that comes on when you kick down on the gas. The power mode causes the gears to shift at a higher RPM for increased acceleration when overtaking.

The JDM 4EAT in my cars also has a power mode, but it is activated by a switch. I traced the wiring and found that the switch connects pin A4 of the TCU to ground. That's the 4th pin of the 1st connector.

Can you post the link of this site please, thanks

After I posted that on the SVX forums, a guy called Nomake Wan compared the wiring on his USDM car and found pin A4 was not connected. So he grounded it to see what would happen. When he put shifter in D, the power mode came on, just like the Japanese cars.:cool:

Since then, a lot of USDM SVX owners have started connecting up switches to enable power mode and the feedback has been overwhelmingly positive. It makes the car feel much more responsive and sporty to drive.

A few guys on the Legacy forums also tried it, but with mixed results. It works for some but not for others. It depends on the firmware version of the TCU.

Maybe it will work for you, maybe not. But it is probably worth trying.
 

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Registered
01 2.5RS White - 4EAT
Joined
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729 Posts
I noticed this on my first RS. I didn't know the JDM one has a switch for it. Awesome find!
 

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Registered
1998 Impreza RS2.5 #29
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93 Posts
I grounded the a4 pin today after work and the difference between when I drove the car before I grounded the pin and the drive after I grounded it was amazing. It feels more responsive as it should and shifted at much higher rpm each time.
 

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Registered
2001 Black 2.5RS
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277 Posts
I wonder how many other people did the same and if there have been problems that resulted from doing this..
 

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Registered
99 Impreza L
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32 Posts
I grounded the a4 pin today after work and the difference between when I drove the car before I grounded the pin and the drive after I grounded it was amazing. It feels more responsive as it should and shifted at much higher rpm each time.
Where exactly did you find the a4 pin? I can't seem to find the right one.
 

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Often Unamused
2001 Impreza RS 2.5
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808 Posts
Someone have pic of the harness on our cars?
 

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Registered
00' Legacy L
Joined
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41 Posts
^ I'd like a picture as well. I will be pulling my motor this weekend and while it's down for repairs this sounds like a good mod I can mess around with.
 

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Premium Member
2001 Subaru Impreza 2.5RS
Joined
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444 Posts
I just bought a 95 gf22 on monday and noticed the power light on the speedo turns on, I was going to post it up on the forums to see what it was but I guess this answers my question :)
 
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