4EAT won't shift out of first - install a switch to make it shift?

[Gloyale]

You could rule out electreical by just unplugging the harne for the trans and going for a drive. The trans should function by hydraulic pressure alone at that point.

[idosubaru]

You could rule out electreical by just unplugging the harne for the trans and going for a drive. The trans should function by hydraulic pressure alone at that point.

NO WAY! really? i had no idea an auto trans would still work, is that true of all transmissions?

 

Skip we have, and hes deep in denial

hey play nice! i do not understand how automatic transmissions work and what they do when certain systems begin to fail. i'd like to understand how the hydraulics, clutches, solenoids, TCU and shifting, and engine all work, but i do not. it's not denial, i'd like to understand that as much as i do engines so i'll keep asking. i'm an engineer i think you can understand my questioning and learning through an experience...as annoying as it may be!

 

- i'm glad this didn't happen to my other one, you'd be blaming it on the Duty C switch!!!!!

[Skip]

"You could rule out electreical by just unplugging the harne for the trans and going for a drive. The trans should function by hydraulic pressure alone at that point."

I would be interested in seeing if this is a fact or a guess.

 

How do solenoids open and close with no electrical input?

 

Is there an over ride function (pilot pressure or line pressure??) that forces them open/closed?

 

Maybe G knows it better, I know I don't.

[idosubaru]

You could rule out electreical by just unplugging the harne for the trans and going for a drive. The trans should function by hydraulic pressure alone at that point.

WTF - YOU'RE RIGHT!! dang it, that is awesome. i was just baffled by that comment and went and pulled the plug...and sure enough it drove!

 

what exactly is it doing, it does drive better, it doesn't seem to stay in first, but what gear was it in? didn't seem to shift, took off a bit slower...like it was starting in second or something?

 

i only went for a short drive but it seemed to have torque bind like this, is that normal?

 

wow GLoyale, that is cool...how many other things like this don't i know...can you make a list? that was awesome. can i unplug my ECU too!!

[johnceggleston]

- i'm glad this didn't happen to my other one, you'd be blaming it on the Duty C switch!!!!!

 

i think it is your duty c switch on your other car, it's a conspiracy.!!

[idosubaru]

I would be interested in seeing if this is a fact or a guess.

i'm still spinning over this, read my last post it does work...definitely someone fill me in what is going on.

[idosubaru]

but before i get too carried away on learning something, i'd like to know what this means in my situation.

 

i guess i need to know how a "good 4EAT" performs this way though, i have no base line. should it drive and shift exactly like normal or be a bit slower and less firm?

 

might also make a difference what it does when it get warmed up...like once it's warmed it might start doing the same thing as it did before (stuck in first).

 

im confused that's all i know, but i went for a drive not too long ago and it wasn't shifting out of first.

[nipper]

i think it is your duty c switch on your other car, it's a conspiracy.!!

 

i agree

 

You really need to get pressure gauges on this. Working on mechanical systems alone you are getting max pressure at all times, which is not normal operation.

 

i still stick with the the dying tranny pump untill some gauges are put on the tranny.

 

nipper

[WoodsWagon]

While nipper may be all excited by a bad front pump causing low line pressure when it warms up, I have a different theory. What else warms up when the car is running? The electronics. If the TCU is having an open when it warms up (thermal expansion of the components), and isn't actually activating the 2n'd clutches solenoid, the tranny will never shift up. You haven't redlined the thing, so it's not seeing an error. If you have a spare TCU, it would make sense to plug it in. Using skip's suggestion of putting a test light on the TCU shift solenoid outputs makes a lot of sense. I wouldn't say replace the tranny untill you're sure the TCU is actually commanding it to shift or not.

[idosubaru]

it's not worth swapping parts. i already AM swapping the transmission, before this ever happened, so that's not a big deal...untimely yes, big deal, no.

 

i think it happens with way too much predictability to just be a failing TCU.

 

i think i'm driving home tonight with it all unplugged, that's just way too cool, i never had a clue you could do that.

[nipper]

it's not worth swapping parts. i already AM swapping the transmission, before this ever happened, so that's not a big deal...untimely yes, big deal, no.

 

i think it happens with way too much predictability to just be a failing TCU.

 

i think i'm driving home tonight with it all unplugged, that's just way too cool, i never had a clue you could do that.

 

 

darn it, someone gave away one of our secrets

 

It may run a bit funny that way, it may last for ever that way. You have just been promoted to test tube

 

nipper

[idosubaru]

You have just been promoted to test tube

awesome. this is not what i was thinking, but exactly what i was looking for. if i can get around town for a month or two that's awesome. thanks Gloyale!

 

pretty sure it's torque binding but like i said i don't give a rip about this trans it's coming out anyway and i don't mind seeing what happens, kind of interested. just drove about 20 miles - did great. i think it's always in 3rd or 4th gear, is that how it works? slow to take off and i can't really feel it shifting at all. is there a "default" gear it's in?

[bulwnkl]

Do I just ask inconvenient questions sometimes?

 

I'm glad to know your findings so far, Gary, and that your transmission is out of first (for now). I'm really interested in whether it'll stay out of first w/o the TCU once it warms up. I'm sticking with my idea that the bad pump thing is bogus until I hear that your transmission won't go into reverse when it's warm. Good luck!

[idosubaru]

I'm really interested in whether it'll stay out of first w/o the TCU once it warms up.

you don't answer inconvenient questions, i thought i answered in another post - it did stay out of first w/o the TCU when warmed up. i drove it 20 miles home after it had already been warm from driving around town (in 1st!). drove home just fine.

 

I'm sticking with my idea that the bad pump thing is bogus until I hear that your transmission won't go into reverse when it's warm. Good luck!

reverse works fine...for now??

 

Gloyale never piped up - i'm still wondering what this means?

[Gloyale]

I'm not totally sure of how it works either. But this is a good sign that you probably DO have pump pressure.

 

Fuji refers to the 4EATs ability to function without electronics, but doesn't describe what the parameters of this "limp" mode are. But just think, If the pump was shot, you'd have low line pressure...ie...... no torque bind, inability to shift up.

[johnceggleston]

disconnecting the trans wire harness removes the E frome the 4Eat. yes you will have torque bind, no E to release the fluid pressure (just like your other car with the switch.)

 

so now you just need to build a 12(?) pin switch for this car so you can start off with the trans wiring connected and then throw the switch to disconnect once you get moving. maybe a switch on the power feed to the TCU would work.....

 

 

or just try a different TCU.

[idosubaru]

i'll reconnect the plug some time and try to pull the transmission codes for kicks just to see. i've tried it before but have never had luck pulling trans codes from an XT6. i've done ABS, Power Steering, and ECU...but trans stuff never seems to work.

 

so you think the pump is good then huh? definitely have torque bind. i may pull the plug on my OBS and see how it drives, to see if it's "about the same".

[bulwnkl]

you don't answer inconvenient questions, i thought i answered in another post - it did stay out of first w/o the TCU when warmed up. i drove it 20 miles home after it had already been warm from driving around town (in 1st!). drove home just fine.

 

reverse works fine...for now??

I'm sorry, Gary, that inconvenient questions remark wasn't directed at you at all. Thank you for posting and for the follow-up.

 

I know you're scheduled to replace this trans anyway, but I'm glad you've (hopefully?) found a way to make it driveable until your desired replacement timeframe. If you find out more about this malfunctioning one's issues, I know I'm interested to hear what you find.

[idosubaru]

i've got other vehicles and i am replacing it so i'm not going to spend much time on it. but i might do a bit of testing, like pull the codes or swap a TPS, and i'll be sure to post back here if i find anything out.

[OB99W]

I've never tried this, so I'm curious; what happens if you manually select first or second with the TCU unplugged?

[idosubaru]

I've never tried this, so I'm curious; what happens if you manually select first or second with the TCU unplugged?

good question. it doesn't do anything. it drives the same in every single gear....which i guess has me thinking - why does REVERSE work???? either going into reverse is strictly mechanical or there's a very limited amount of electrical activity?

[OB99W]

[...]why does REVERSE work???? either going into reverse is strictly mechanical or there's a very limited amount of electrical activity?

As far as I know, the TCU is inactive in reverse; operation in that gear is determined by the manual valve position.

Assuming the inhibiter switch is functional, the TCU should normally know what gear is selected; with the TCU disconnected, it should revert to whatever control the manual valve allows anyway.

[johnceggleston]

the 4eat is an electronicly control 4 speed automatic, not a 4 speed automatic with a computer. DUH, you all know this.

 

end wrench refers to the disconnected trans wiring situation as "fail safe mode". this means you can limp the car home if the wiring or the tcu fails. but obviously, the trans doesn't work like a 4 speed A/T without the TCU.

 

i don't know what gear it defaults to (rpm vs. speed may give you a clue), but it can't find some of them with out the computer. again, DUH.

 

obviously reverse is a mechanical gear selection not electronic.

[idosubaru]

i don't know what gear it defaults to

it's 3rd on an XT6.

[crazyhorse001]

My uneducated 2cents worth:

 

The gear selector on most electronic autos is just a series of switches. I'm guessing that you could do a full manual setup by wiring the selector switches to thier respective solenoids. I've seen it done on a Ford AXOD in a SHO Taurus. Granted you'll have to be the E part of the 4Eat. doing ALL the shifting yourself.