TCM Bypass switch????

[teamwestoutdoors]

Hey gang, I need your help on a way to bypass the Transmission Control Module (TCM) (under the glove-box) on my 90 XJ Limited 4.0, AW4, 6.5” lift on 33’s D30, D35. I have been having all the same problems with my Tranny “Slipping” as a lot of you have. I have read a bunch of the posts and comments on adjusting TPS, TV cables, TCM, and Solenoids. I’ve done the “Dumb Test” and my Tranny has great power with the TCM unplugged, so I know it’s electrical. With that said, I want to just hard wire in a switch box that will allow me to shift between gears and bypass the TCM. Any help here?

 

[87manche]

just wire a simple toggle switch into the power wire.
Switch closed=TCU power
switch open=TCU no power. simple as that. I think it's the yellow wire, don't quote me on that one.

 

[teamwestoutdoors]

just wire a simple toggle switch into the power wire.
Switch closed=TCU power
switch open=TCU no power. simple as that. I think it's the yellow wire, don't quote me on that one.

That was what I first was going to do. But, if I do that then I will not have 2nd gear, right? As 1st and 2nd share the same slot on the shift handle.

 

[Johnnie Walker]

If you search, maybe a link at the bottom of the page there is a way to "switch" 2nd gear. and also manual TC lockup.

 

[87manche]

yes, find the wiring diagram and you can use 2 toggle switches to control the solenoids in the trans, just like the TCU does.

you could also just go full manual with an aw4shifter

 

[tbburg]

Not sure manual control of the solenoids will solve the problem. If it's shifting OK in manual mode, and slips under elec. control, it sounds like it might be a solenoid problem. You might try getting a junkyard trans computer and swapping it in, 'see if the problem goes away.

As far as full manual control, look into the Baja:
http://www.naxja.org/forum/showthread.php?t=996009

 

[joe_peters]

Moving this to Mod Tech.

 

[R.DesJardin]

Not sure manual control of the solenoids will solve the problem. If it's shifting OK in manual mode, and slips under elec. control, it sounds like it might be a solenoid problem. You might try getting a junkyard trans computer and swapping it in, 'see if the problem goes away.

As far as full manual control, look into the Baja:
http://www.naxja.org/forum/showthread.php?t=996009

tbburg, thanks,
Might just look at the Rail shift controller and switch setup from here http://www.radesignsproducts.com , make sure the solenoids are good first, or the slipping just might be the TCM is starting you out in 3rd or 4th?

 

[teamwestoutdoors]

Not sure manual control of the solenoids will solve the problem. If it's shifting OK in manual mode, and slips under elec. control, it sounds like it might be a solenoid problem. You might try getting a junkyard trans computer and swapping it in, 'see if the problem goes away.
As far as full manual control, look into the Baja:
http://www.naxja.org/forum/showthread.php?t=996009

When you say, "Trans Computer" do you mean TCM/TCU? I have a donor XJ and have swapped in and out TCM's with no change. Is there a way to check solenoids without opening up the tranny?

 

[R.DesJardin]

This is the unconnected TCM/TCU test, or called limp mode when the TCM/TCU fails.

Without guidance from the TCM, the transmission is supposed to react to the shifter position as follows:

1-2 : Stay in 1st
3: Stay in 3rd
D: Stay in Overdrive.

This is good to know if you need to limp home. Just pretend it's a manual.

 

[Johnnie Walker]

When you say, "Trans Computer" do you mean TCM/TCU? I have a donor XJ and have swapped in and out TCM's with no change. Is there a way to check solenoids without opening up the tranny?

Tap into the TCU wires for the solenoids and drive/use the switches. For 2nd gear both solenoids are on.
Also, when was your trans fluid last changed?

 

[87manche]

Is there a way to check solenoids without opening up the tranny?

You can check them with meter set to ohms at the connector.
You'll have to search for the detailed procedure and the ohm spec, most solenoids are between 15-20 ohms when good. An open circuit is bad, so is a dead short.

That's as good as it gets without taking the valvebody out, you can't truly function check them without taking the VB out and putting voltage to them.

This is why my junk is 5 speed.