Everything you ever wanted to know about the AW4

[lawsoncl]

/screenshot of very first page in this thread/

Yes, the above is correct. Welcome to !

 

[SYE88XJ]

Great, so swapping the tailhouse but not needing to mess with gearing.

Thanks y'all, I appreciate the fast sharing of expertise and the warm welcome.

 

[Frank Reiner]

kastein:


Re: 98-01 XJ TCU


What information is exchanged over the CCD line, and how is it used by the TCU?

 

[lawsoncl]

AFAIK, the only info is from the TCU checking in to say it's alive or it's got a trouble code. The TCU handles the shifting independent of the engine computer.

 

[RCP Phx]

That's not all, the ecu also reports the map, throttle position, and the manifold vacumm. The TCU compares that to the output speed sensor to help control shift points and torque converter lock-up.

 

[Frank Reiner]

AFAIK, the only info is from the TCU checking in to say it's alive or it's got a trouble code. The TCU handles the shifting independent of the engine computer.

Given the apparent simplicity of control parameters, this has been my conclusion also.

That's not all, the ecu also reports the map, throttle position, and the manifold vacuum. The TCU compares that to the output speed sensor to help control shift points and torque converter lock-up.

Manifold pressure, RPM, and coolant temperature COULD be used as modifying parameters, although there does not seem to be any documentation of that.
Throttle position, via TPS voltage, is a direct input.

 

[Frank Reiner]

AFAIK, the only info is from the TCU checking in to say it's alive or it's got a trouble code. The TCU handles the shifting independent of the engine computer.

Given the apparent simplicity of control parameters, this has been my conclusion also.

That's not all, the ecu also reports the map, throttle position, and the manifold vacuum. The TCU compares that to the output speed sensor to help control shift points and torque converter lock-up.

Manifold pressure, RPM, and coolant temperature COULD be used as modifying parameters, although there does not seem to be any documentation of that.
Throttle position, via TPS voltage, is a direct input.

 

[kastein]

That's not all, the ecu also reports the map, throttle position, and the manifold vacumm. The TCU compares that to the output speed sensor to help control shift points and torque converter lock-up.

That's interesting. The TCU has a dedicated signal wire for the TPS, so not sure why it would need it via CCD bus as well. Map and manifold vacuum are the same thing.

I do not have any good info on this though. It is something I would like to know, but I will need to take the data collection myself to really be happy with putting my name on a list of data points it shares with the ECU.

 

[Frank Reiner]

That's interesting. The TCU has a dedicated signal wire for the TPS, so not sure why it would need it via CCD bus as well. Map and manifold vacuum are the same thing.

I do not have any good info on this though. It is something I would like to know, but I will need to take the data collection myself to really be happy with putting my name on a list of data points it shares with the ECU.

What are the chances that the TCU would receive and use engine RPM and manifold pressure?

 

[xjdavid1]

I have a 95 XJ and am thinking of swapping in a 98 AW4.

From the write up at beginning of this thread it says that a change to the t-case input gear is required.

"1998-2001 AW4s require more work. All the transfer case input gear info from 1990.5-1997 applies, on top of that, the sensors have changed!"

I see that both years have the 23 spline output shaft in the auto so whats different or needs changing?


Sent from my SM-N960F using Tapatalk

 

[RCP Phx]

I have a 95 XJ and am thinking of swapping in a 98 AW4.
From the write up at beginning of this thread it says that a change to the t-case input gear is required.
"1998-2001 AW4s require more work. All the transfer case input gear info from 1990.5-1997 applies, on top of that, the sensors have changed!"
I see that both years have the 23 spline output shaft in the auto so whats different or needs changing?Sent from my SM-N960F using Tapatalk

From page 1 -
1998-01, the AW4 changed electrically, but is otherwise the same as 1990.5-1997 units. The Output Speed Sensor changed from a 1pps reed switch to a 4 pulse/rev variable reluctance pickup similar to the RENIX CPS and most ABS wheel speed sensors. A 16 pulse/rev Input Speed Sensor was also added. The ISS and OSS for these years are the same part number; one may be substituted for the other for spare parts purposes.

 

[lawsoncl]

I have a 95 XJ and am thinking of swapping in a 98 AW4.

Unless you plan to swap some internals between a pre-98 AW4 or build some electronics, that rear sensor is going to trigger 4x as fast and the 1995 trans computer will have you in 4th gear by the time you hit 20 mph. So you want to stick with a 1990.5-1996 23-spline donor. A 1997 donor is doable, so long as you don't mind some wire splicing to fix the the electrical connectors being mismatched.

 

[xjdavid1]

Ok so I should be good if I change the extension housing and reluctor ring and sensor off my 95 and put it on the 98.

The pin outs on my 95 plug makes reference to 4WD sense which I assume gos nowhere as the 4WD switch is on the T-case. Is this correct?

Cavity 1 is 4WD Sense and it has a wire both sides of the connector?
Cavity 7 is 4WD Indicator lamp which has a wire both sides of the connector?

I can't imagine what these wires are for as the wiring for the 4wd switch on the t-case comes up to a different plug c129.

 

[Unclewolverine]

I dint know about your plugs but lawsoncl is wrong. I put a 2000 aw4 in my 95. You only need to change the reluctor wheel and extension housing and change the trans wires slightly, most people drop the pan and just swap the harness, but mine was to brittle so I just cut and soldered.

 

[lawsoncl]

I think you're referring to this:

Unless you plan to swap some internals between a pre-98 AW4

I dint know about your plugs but lawsoncl is wrong. I put a 2000 aw4 in my 95. You only need to change the reluctor wheel and extension housing and change the trans wires slightly, most people drop the pan and just swap the harness, but mine was to brittle so I just cut and soldered.

Internals wasn't the right choice of words, as that implied opening up the main portion of the trans. You do need to pull the back tailcone or extension housing and swap the rear sensor rotor as you mentioned and shown a few pages back.

 

[xjdavid1]

Does anybody know what year valvebodies can be fitted to 95 Aw4. I have noticed that the check ball placement diagram in my 95 FSM lines up with the 96 model in the ATSG diagram not the 95. I have just had a shop fit another valvebody of unknown year and now it is slamming into reverse which ATSG information tells me it has to do with check balls.

 

[kastein]

What are the chances that the TCU would receive and use engine RPM and manifold pressure?

I do not know for sure but I think it is pretty unlikely. I am not comfortable answering this any more definitively than that without actually reading the TCU firmware code, which I have wanted to do for a decade now but have been unable to buy the adapter board to put the TCU MCU in my EPROM programmer anywhere for less than several hundred dollars. Since this is a hobby project that is well outside of the amount I am willing to spend.

I have a 95 XJ and am thinking of swapping in a 98 AW4.

From the write up at beginning of this thread it says that a change to the t-case input gear is required.

"1998-2001 AW4s require more work. All the transfer case input gear info from 1990.5-1997 applies, on top of that, the sensors have changed!"

I see that both years have the 23 spline output shaft in the auto so whats different or needs changing?


Sent from my SM-N960F using Tapatalk

I need to go re-read my own first post and make sure I didn't make a mistake on that I suppose. The intention was to indicate that 90 down vs 90.5 up (possibly 90 vs 91, my info sources differ on this) are 21 vs 23 spline so you would not need to change your input gear between 95 and 98. However the OSS pulse count and signal type (reed vs variable reluctance) are different as everyone has already noted and this will not work right without swapping at least the reluctor wheel, tailhousing, and sensor. Additionally the output shaft is actually slightly different between 97- and 98+ (the snap ring grooves are in different places) and you may or may not be happy with the half-assing that is necessary to make the wrong year reluctor wheel fit a given output shaft. This all leads me to generally recommend staying with the correct year range transmission as there is typically no shortage of them, they fail rarely enough that the availability is high and the price is low.

 

[Unclewolverine]

I do not know for sure but I think it is pretty unlikely. I am not comfortable answering this any more definitively than that without actually reading the TCU firmware code, which I have wanted to do for a decade now but have been unable to buy the adapter board to put the TCU MCU in my EPROM programmer anywhere for less than several hundred dollars. Since this is a hobby project that is well outside of the amount I am willing to spend.


I need to go re-read my own first post and make sure I didn't make a mistake on that I suppose. The intention was to indicate that 90 down vs 90.5 up (possibly 90 vs 91, my info sources differ on this) are 21 vs 23 spline so you would not need to change your input gear between 95 and 98. However the OSS pulse count and signal type (reed vs variable reluctance) are different as everyone has already noted and this will not work right without swapping at least the reluctor wheel, tailhousing, and sensor. Additionally the output shaft is actually slightly different between 97- and 98+ (the snap ring grooves are in different places) and you may or may not be happy with the half-assing that is necessary to make the wrong year reluctor wheel fit a given output shaft. This all leads me to generally recommend staying with the correct year range transmission as there is typically no shortage of them, they fail rarely enough that the availability is high and the price is low.

I have had a 2000 aw4 in my 95 for over 100k miles and can confirm it works fine by just changing the reluctor wheel and tail housing. (And necessary wire changes.)

 

[kastein]

Your definition of "works fine" and mine are different. That's OK, but I prefer to provide all the gory details and allow other people to decide if they are OK with the compromises or other parts changes necessary to achieve an OEM-equivalent fit and finish, or if they want to choose another route. That's why I mention things as simple as having to splice 3 wires or swap a harness to put a 97 AW4 in a 91-96 in the first post in the thread - and note that I have literally been sent death threats for not explaining in EVEN MORE detail exactly which wire color codes to connect to which on that harness, so amazingly, I am not the most pedantic person out there on this front. I know, I'm as surprised as you are.

 

[Macc]

What happens if you zip-tie your shift pressure line to be at "wide open" all the time?