simple question, is there a simple answer???

simple question, is there a simple answer???

Hydraulic pressure and electronic signals. So, no, there isn't a simple answer (that would help much in diagnosis).

 

More-complex answers:

http://endwrench.com/pdf/feb2004pdf/4EAT.pdf (phase 1)

http://endwrench.com/images/pdfs/4EAatPh2Win04.pdf

http://endwrench.com/images/pdfs/1999Info.pdf

http://endwrench.com/images/pdfs/4EAT.pdf

http://www.endwrench.com/pdf/drivetrain/02Winter4EATDiagServ.pdf (ph2)

Differential fluid correction to "4EATDiagServ":

http://endwrench.com/images/pdfs/4EATService.pdf (ph2)

http://www.endwrench.com/pdf/drivetrain/02Winter4EATTransOp.pdf (ph2)

1995 4EAT diags/links:

http://www.ultimatesubaru.org/forum/showthread.php?t=19805

I see a coupla things there...

 

1) I wonder why the ABS runs a signal in- no traction control on this critter...

 

2) I assume "Transfer Duty Solenoid" is aka the "Duty C" solenoid?

 

3) If I were to cut the ^%%^^ cruise control signal, will it stop being MORE prone to downshifting on hills with the cruise on?

 

4) If I take that same cruise control signal and run it to a switch (with the right voltage, aka gnd or +5 or +12) can I use it as a 'sport shift' signal?

 

 

I realize 3,4 may induce some heartburn as the subie literature says the trans is supposed to be less sensitive to loading with the cruise on, but on mine, I can assure, attest, and prove that ain't the case!

 

With the cruise on, it downshifts up hills that don't require a downshift, and if I kill the cruise I can maintain speed with no downshift, so I'd really like to keep the TCU from knowing the cruise is on.

 

 

Dave

And add to that:

- the torque control signals?

- the dropping register signals?

 

 

Dave

simple question, is there a simple answer???

 

Nothing is ever simple.

 

But ill give you a basic course (which everyone should know how things worked pre computer to understand computer controlled).

 

In the good old days... you had the front pump (still exists). This makes the line pressure that makes everything possible. You had the throttle position (eithe a cable to a valve or a vacum modulator) and a govenor (to detect road speed).

 

The valve body is basically a hydraulic computer. The balancing act is throttle position vs govenor output.

 

http://auto.howstuffworks.com/automatic-transmission.htm

 

In a modern transmission, alot of the vlave body has been replaced by solenoids for automatic shifting. The govenor has been replaced by the vehical speed sensor. The modulator has been replaced by an input from the ECU to the TCU.

 

There is some program fiddling to soften the shifts, things that could never have been done with the old valve body, ie reducing engine torque during a shift, engaging two gears at the same time during an upshift to name just two.

 

Like everything else under the hood, nothing really has changed since the automatic was invented, just the way it is managed has been changed (and of course materials).

 

 

nipper

1) I wonder why the ABS runs a signal in- no traction control on this critter...

I believe the trans shifts into 3rd when the ABS activates.

 

 

2) I assume "Transfer Duty Solenoid" is aka the "Duty C" solenoid?

That would be true AFIAK.

 

 

3) If I were to cut the ^%%^^ cruise control signal, will it stop being MORE prone to downshifting on hills with the cruise on?

I think it would be even more prone to downshifting then. When the cruise is on, the trans holds higher gears moreso than when its off. I don't know why yours would act differently. It might be simply because the tuning of the cruise control is poor. It reacts too slowly to a speed drop when hitting the hill, then tends to freak out and suddenly yank the throttle way open to compensate. It is poor tuning of the control loop during engineering.

 

4) If I take that same cruise control signal and run it to a switch (with the right voltage, aka gnd or +5 or +12) can I use it as a 'sport shift' signal?

hehe maybe an anti-sport shift as it will want to hold higher gears moreso than with your foot on the throttle.

The downshifting on hills with cruise on, almost all cars do that now, and they downshift two gears. I even rented a car with a v-8 and it did the same thing.

 

The best way to deal with the cruise on hills, is either put the car in D3 if there are a lot of hills, or press the skinny pedal with your right foot to slowly feed throttle so the cruise doesnt ask for a down shift.

 

nipper

...or press the skinny pedal with your right foot to slowly feed throttle so the cruise doesnt ask for a down shift.

Yes that is a great idea, I do that often. In control systems that action is called feed-forward control. Like you know what is coming up, so you let the system know that so it can preact, rather than simply react.

Having this connected makes watching it all

happen kewl

 

http://www.ultimatesubaru.org/forum/showthread.php?t=54985

wow skip that is awesome and a great idea! I read the other thread. Very interesting!

But then where would i put my scangauge?

 

 

nipper

thanks Porc,

Coming form a Guru such as youself

that means alot,

I repeat, thanks again.

But then where would i put my scangauge?

Hm....good point nipper! So many gauges and gadgets, so little space! Even Night Rider would be envious!

Hm....good point nipper! So many gauges and gadgets, so little space! Even Night Rider would be envious!

 

Right now im trying to figure out how to mount garmin so no one will steal it out of the car. We are in a hot spot for GPS thefts.

 

 

nipper

I believe the trans shifts into 3rd when the ABS activates.

 

 

That would be true AFIAK.

 

 

I think it would be even more prone to downshifting then. When the cruise is on, the trans holds higher gears moreso than when its off. I don't know why yours would act differently. It might be simply because the tuning of the cruise control is poor. It reacts too slowly to a speed drop when hitting the hill, then tends to freak out and suddenly yank the throttle way open to compensate. It is poor tuning of the control loop during engineering.

 

hehe maybe an anti-sport shift as it will want to hold higher gears moreso than with your foot on the throttle.

 

 

Unless the cruise control can be 'tuned' better (BTW, the car does not slow much at all before downshifting), then does anyone know if cutting that 'cruise control' signal lead would do what I'm hoping for?

 

Dave

You may throw some codes, the cruise control may not work at all...a couple of possabilities. Don't cut the wire, just disconnect it and see what happens.

 

Remember though, its alos not good for the car to not downshift, as you can lug the engine. If cutting the wire stops the engine from downshifting, that would still require your intervention, so just pushing the small pedal may just be simpler.

 

It's worth a try.

 

nipper

You may throw some codes, the cruise control may not work at all...a couple of possabilities. Don't cut the wire, just disconnect it and see what happens.

 

Remember though, its alos not good for the car to not downshift, as you can lug the engine. If cutting the wire stops the engine from downshifting, that would still require your intervention, so just pushing the small pedal may just be simpler.

 

It's worth a try.

 

nipper

 

 

Well, at worst it would cause it to downshift only at the same point it would if the cruise was off, if it just tells the TCU the cruise is active.

 

Dave