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Add power/comfort switch to later xj's?

P

pressurerat

NAXJA Forum User
Location
Tennessee
Can this be done without copious amounts of work? I have exhaustively searched not only this forum but others and the web as well with no real definitive answers, only more questions. Has anyone here actually done this with success? I would like to add it to my 93, I actually like the feature from owning a couple of renix xj's. So the question is, 'can it be done?' , not 'why do you want to do it?'. TIA!!!

:smoker:
 
I don't know if the circuitry exists in the later TCUs (it may,) but I do have to ask why you want to do it? Later AW4 controllers were hardwired (somewhere...) into "Power" mode - the "Comfort" mode does accelerate wear on the internal clutches somewhat. How? It's akin to doing "speed shifts" vice "soft shifts" with a manual - when you do a softer shift, you take longer to fully engage the clutch - meaning that it slips more until you "lock" it in place. Same thing happens in your automatic - instead of one large clutch, tho, you have about 25 smaller clutches operating in a "wet bath."

It probably can be done - but I just wanted to let you know that you might accelerate wear on your transmission doing so. If you need to change TCUs (I'm not sure, but it's fairly likely...) I can come up with a RENIX unit for you from my spares bin - "worked when pulled."

Not trying to dissuade you from the mod - just letting you know what you may be in for. The wiring for the switch probably doesn't exist, and I don't know about internal circuitry in the TCU (haven't checked that yet.)
 
I am aware of the risk involved with the premature wear issue, thanks for noting this. I just like the feature- nothing more or less. I have a local U-pull it junkyard with dirt cheap prices. The are always stocked with plenty of renix era 4.0 XJs. I assumed I would need the TCU and of course the switch, but the wiring is my main issue. Thanks for the reply 5-90!
 
Fairly easy to try. The C-11 pin (tan wire) at the TCU is the "power switch" pin for both the Renix and yours.
The only difference is the Renix routed 12 volts from the fuse block trans fuse, through the switch to the C-11 pin.
And on yours the C-11 pin is powered directly from the PCM through the tan wire. The PCM switches it into power mode.
Snip off the C-11 (tan) wire four inches from the TCU, wire in a switch. Power to the switch from a fused source (maybe 3 amps) and try it out.
I doubt the PCM TCU connection at C-11 has any affect on the PCM, it may, if a problem shows up reconnect the snipped wires and solder them back together.

If you really want to give it a try, I can cut and paste some diagrams for you.
 
8Mud said:
Fairly easy to try. The C-11 pin (tan wire) at the TCU is the "power switch" pin for both the Renix and yours.
The only difference is the Renix routed 12 volts from the fuse block trans fuse, through the switch to the C-11 pin.
And on yours the C-11 pin is powered directly from the PCM through the tan wire. The PCM switches it into power mode.
Snip off the C-11 (tan) wire four inches from the TCU, wire in a switch. Power to the switch from a fused source (maybe 3 amps) and try it out.
I doubt the PCM TCU connection at C-11 has any affect on the PCM, it may, if a problem shows up reconnect the snipped wires and solder them back together.

If you really want to give it a try, I can cut and paste some diagrams for you.
Click to expand...

If he's not interested, I am - so could you do it anyhow? I don't have access to all my FSMs at the moment, and I'm busy with other things (and I'm not a huge fan of reinventing the wheel anyhow - why duplicate work that someone else has already done?:doh: )
 
ehall said:
It's also on the non-Renix 91 (mine) so it should be doable on everything up to 96 (OBD-II changes too much to make it "simple")
Click to expand...

So, then, it sounds like the TCU didn't change - and the circuit just went unwired. I'd thought it was eliminated for the 1991MY - but I've been wrong before!:laugh3:
 
2qjdocj.png



The first is for an 88, the second for a 93.

292tok9.jpg


Looking closer at the schematic I may be mistaken about the power coming from the PCM, I'll have to dig a little deeper and see exactly where it comes from and figure out what an ECE connector is.
 
Last edited:
Just some stuff I picked up on the web, likely Chryco.
 
So, looking over both diagrams, all that needs to happen is to figure out of the later TAN wire going into TCU C11 carries +12VDC constantly - if it does, just wire in a toggle switch. Should be a fairly small signal, since it's a logic switch, right?

An illuminated toggle can be used in a similar manner to the OEM. Hell, I might have some OEM switches running about, if the 1991-1995 IP style is the same as the RENIX (probably is.) If you want pix for comparison, let me know.

This is turning out to be an interesting project - if only for academic value.
 
5-90 said:
So, then, it sounds like the TCU didn't change - and the circuit just went unwired. I'd thought it was eliminated for the 1991MY - but I've been wrong before!:laugh3:
Click to expand...


Some 91's definately had the switch and I've heard some 92's had it, not sure on the 92.
 
So am I to understand that on the power switch models, the switch simply supplies 12v to the c11 pin. And without the 12 volts, the shift points merely change?
 
pressurerat said:
So am I to understand that on the power switch models, the switch simply supplies 12v to the c11 pin. And without the 12 volts, the shift points merely change?
Click to expand...

Yes. The shift points, how readily it kicksdown, timing of when the t/c locks up all change.
 
I know this sounds like a dumb question since the switch does the same thing, but that wont 'hurt' the tranny right? Thanks for all of the input eveyone so far!!!
 
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