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Unread 05-17-2013, 05:12 PM   #1
Sparrows
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AW4 Overdrive help

Hey hey,

So I've had a problem with my trans since I picked up my YJ. The PO had a 4.0/aw4 swapped into it from an XJ. I finally figured out what is interfering with my overdrive.

I'm hoping one of the XJ guys can help me out since I'm running an XJ drivetrain.

The problem I'm having is that my overdrive doesn't work when my headlights/turn signals are on. I can literally be driving down the road at 65mph, flip on my headlights or blinker, and my OD shuts down and won't reengage until after I turn off the headlights/blinker.

The shop owner that did the swap mentioned that he thought that my tail lights are probably getting too much power when the lights/blinkers are on and that it's confusing the trans computer and making it think that I'm hitting the breaks.

He told me he would get it fixed two months ago. He's a one man shop, and bailed out on me four times, and hasn't returned any of my calls/emails/texts/PMs for over a month now so it's time to deal with this on my own. :

What can I do to fix this? I really need help as this makes my Jeep undrivable after dark and since this is my DD it's really been a huge PITA. Thanks in advance for any help/advise!

Cheers


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Unread 05-17-2013, 05:23 PM   #2
tjwalker
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I'd certainly start with grounds. They can be responsible for many strange happenings on your XJ!
---------------------------------------------------------------------------------
Grounds can be the root cause of many electrical gremlins. Refreshing grounds is NEVER a bad idea, and the investment of your time in this procedure is always well worth it!

You can't tell much of anything by looking at ground connections!! You must remove, scrape, clean until shiny the cable/wire ends and whatever they bolt to. Be sure to remove all paint from any ground connections.

Start with the one on the back corner of the head, and where it attaches to the firewall, as it deteriorates over time and is an area that makes it susceptible to damage. Best to replace that woven cable with a #4 or #2 gauge cable. You can attach the one end to the intake manifold if you would like.

Next go over to the engine dipstick tube stud. Remove the nut and clean the wire ends and scrape the block until shiny at the stud. Reattach tightly.

If you are so inclined, add at least a #6 cable from the negative terminal of your battery to one of the bolts on your radiator support.
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Unread 05-17-2013, 06:50 PM   #3
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Quote:
Originally Posted by tjwalker View Post
I'd certainly start with grounds. They can be responsible for many strange happenings on your XJ!
---------------------------------------------------------------------------------
Grounds can be the root cause of many electrical gremlins. Refreshing grounds is NEVER a bad idea, and the investment of your time in this procedure is always well worth it!

You can't tell much of anything by looking at ground connections!! You must remove, scrape, clean until shiny the cable/wire ends and whatever they bolt to. Be sure to remove all paint from any ground connections.

Start with the one on the back corner of the head, and where it attaches to the firewall, as it deteriorates over time and is an area that makes it susceptible to damage. Best to replace that woven cable with a #4 or #2 gauge cable. You can attach the one end to the intake manifold if you would like.

Next go over to the engine dipstick tube stud. Remove the nut and clean the wire ends and scrape the block until shiny at the stud. Reattach tightly.

If you are so inclined, add at least a #6 cable from the negative terminal of your battery to one of the bolts on your radiator support.
That almost reads like an automated response lol.
I've gone through almost all the grounds at this point. In fact my entire Jeep is wired together with a Painless harness and most, if not all, the grounds were cleaned and replaced/repaired during the installation.

I was told that I could possibly be getting "feedback" from the tail lights to the transmission controller when the lights are on and that putting an inline diode in could solve the issue. This all sounds kind of foreign to me, so does that sound like a possibility?

Cheers
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Unread 05-17-2013, 07:06 PM   #4
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Diodes are one-way valves for electricity. They are inexpensive and simple to install. I would try a few 12 volt diodes on ground wires to the AW-4 and the transmission controller.

I would also look into which circuit and where the trans control is spliced into to get its power from.
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Unread 05-17-2013, 07:16 PM   #5
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Quote:
Originally Posted by CJ7-Tim View Post
Diodes are one-way valves for electricity. They are inexpensive and simple to install. I would try a few 12 volt diodes on ground wires to the AW-4 and the transmission controller.

I would also look into which circuit and where the trans control is spliced into to get its power from.
Ok, awesome.
I know what a diode does, but wasn't sure if it made sense for this application. So I'll want to put it on the ground and not the hot wire? I'll run by RadioShack tomorrow and grab a handful of them and try to figure it out.

Any other thoughts/ideas would be appreciated.

Cheers

EDIT: anyone have a decent wiring diagram of the TCU? It would be helpful to figure out which wires could be causing my problems....Preferably something for dummies haha! D:

EDIT 2: Some more googling and I found this;


So looking at that, I would want to diode the break switch right? Since it's my tail lights that are causing the issue with "feedback" to the break switch, making the trans think that I'm hitting the breaks and unlocking the torque converter? Or am I way off base here?

Thanks a bunch all!
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Unread 05-17-2013, 07:40 PM   #6
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I am not a E-tech at all, I just know a few things and am good at figuring out stuff. I would think you have stray voltage that is finding a ground wire, and then feeding back to the Trans Control (TCU). There are at least 2 versions of the AW-4 TCU, maybe more, so you need to get the Jeep Part Number from the TCU itself to find the correct wire diagrams.


Add a diode temporarily wherever you think it will help. They will do no harm, and you can remove them if they cause any additional strange AW-4 behaviors.
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Unread 05-17-2013, 07:46 PM   #7
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Hitting the brakes causes the torque converter to unlock. It doesn't cause the transmission to downshift.
When you are in OD, solenoids 1 and 2 are both off. Energizing solenoid 2 causes the transmission to shift into 3rd.
Look for an 18 gauge violet/white wire between the TCU (under the passenger side dash on an XJ, not sure where yours is) and the transmission.

Hope this helps.
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Unread 05-17-2013, 08:33 PM   #8
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Quote:
Originally Posted by CJ7-Tim View Post
I am not a E-tech at all, I just know a few things and am good at figuring out stuff. I would think you have stray voltage that is finding a ground wire, and then feeding back to the Trans Control (TCU). There are at least 2 versions of the AW-4 TCU, maybe more, so you need to get the Jeep Part Number from the TCU itself to find the correct wire diagrams.

Add a diode temporarily wherever you think it will help. They will do no harm, and you can remove them if they cause any additional strange AW-4 behaviors.
I know almost nothing about auto trans, so I have no idea where they would help lol. That' what the JF guys are for haha!

I'll figure out which one I have and report back.

Quote:
Originally Posted by sAe23 View Post
Hitting the brakes causes the torque converter to unlock. It doesn't cause the transmission to downshift.
When you are in OD, solenoids 1 and 2 are both off. Energizing solenoid 2 causes the transmission to shift into 3rd.
Look for an 18 gauge violet/white wire between the TCU (under the passenger side dash on an XJ, not sure where yours is) and the transmission.

Hope this helps.
That actually does help. I think....
So my understanding (correct me if I'm wrong) is that the torque converter locking up is pretty much overdrive. You have 1-4 and then 4th with the converter locked up, aka OD. Yes or no?

Now that you say that, I'm not actually sure if it's downshifting or just falling out of OD (torque converter unlocking?). I can drive down the freeway at 65, turn my blinker on or my headlights, and get a 500+ jump in RPMs until I turn the lights back off. It's bad enough that I can't get over about 55mph with the headlights on without pushing the motor into dangerously high sustained RMPs.

In fact, the motor changes RPM with the blinkers blinking. It bounces with the flashing of the blinker...

Would a video help? I can take one tomorrow.

Adding multiple diodes wouldn't be that bad to solve the issue, I just need to know where to start splicing them in. My TCU is just tucked under the dash. Are you telling me that the violet/white wire the control wire for solenoid 2? If I'm understanding you, you're thinking that solenoid 2 is getting the feedback somehow and kicking it into 3rd.

Thanks again!

Cheers
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Unread 05-18-2013, 08:38 AM   #9
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The AW-4 goes into OD by locking the Torque Converter (TC) at about 45-48 mph. Locking and unlocking feels almost like a gear shift feels. You can drive in 3rd (thus no OD lockup) on the highway with no harm to the engine or transmission.

I would guess that whoever installed the transmission choose the wrong wire to hook the TCU brake sensing circuit to, to or that it has stray voltage. Normally the TCU unlocks the TC from OD when you step on the brakes so the transmission can downshift when you come to a complete stop. You can lightly touch the brake pedal enough to trigger the brake lights and the Torque Converter will unlock and you should see a 3-600 rpm jump on the Tach.

I would put some diodes on the brake pedal switch wires and on the TCU ground wires. I would guess that the brake pedal switch is where the TCU gets its brake lamp signal from.

The Aisin-Warner four-speed automatic transmission (AW4) was co-designed by AMC and Borg Warner then built by Aisin in their new facility for use in then all new Cherokee XJ's new in-line six-cylinder 4.0 L design. It was manufactured by Aisin-Warner, a member of the Toyota group, in partnership with Borg-Warner. It shares many parts with the Aisin 450-43LE that is used in Toyota off-road vehicles.

Gear Ratios for the AW4:

1st: 2.80
2nd: 1.53
3rd: 1.00
4th: 0.75 (23-spline, 0.705 21-spline)
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Unread 05-18-2013, 11:10 AM   #10
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Quote:
Originally Posted by CJ7-Tim View Post
The AW-4 goes into OD by locking the Torque Converter (TC) at about 45-48 mph. Locking and unlocking feels almost like a gear shift feels. You can drive in 3rd (thus no OD lockup) on the highway with no harm to the engine or transmission.

I would guess that whoever installed the transmission choose the wrong wire to hook the TCU brake sensing circuit to, to or that it has stray voltage. Normally the TCU unlocks the TC from OD when you step on the brakes so the transmission can downshift when you come to a complete stop. You can lightly touch the brake pedal enough to trigger the brake lights and the Torque Converter will unlock and you should see a 3-600 rpm jump on the Tach.

I would put some diodes on the brake pedal switch wires and on the TCU ground wires. I would guess that the brake pedal switch is where the TCU gets its brake lamp signal from.

[sic]
Thank you. That is exactly what is going on! This has been plaguing me since I bought this Jeep. For months I couldn't figure out what was going on and why the trans was acting so stupid. I'm one of those people that almost always drives with the headlights on (see and be seen) and as such, whenever I would get on the freeway, everything would be running at far too high of an rpm range, and I would pop the idiot light (trouble codes read that the knock sensor was deactivating due to too much chatter from the motor from the high sustained rpm) and I thought it was my knock sensor itself causing the issues. :

I tried a bunch of fixes for that, including replacing the knock sensor with no luck. One day I was driving home from a trail run and was going about 65 down the highway when I realized I forgot to turn on my headlights. The second I turned them on my Jeep downshifted. Wtf? I turned the lights on and off, on and off, over and over, and that was my "ah-ha" moment when I realized what the problem was!

The shop that did the install was supposed to get me in to get it fixed (under warranty still) but I've been blown off so many times now I just decided to figure out how to fix it myself and be done with it.

Thanks for all the awesome support. I'll be digging into it in the next few hours. I'll report back in as things progress.

THANKS!

Cheers
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Unread 05-18-2013, 09:58 PM   #11
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Quote:
Originally Posted by Sparrows View Post
[snip]
So my understanding (correct me if I'm wrong) is that the torque converter locking up is pretty much overdrive. You have 1-4 and then 4th with the converter locked up, aka OD. Yes or no?

Now that you say that, I'm not actually sure if it's downshifting or just falling out of OD (torque converter unlocking?).
[snip]

Are you telling me that the violet/white wire the control wire for solenoid 2? If I'm understanding you, you're thinking that solenoid 2 is getting the feedback somehow and kicking it into 3rd.

Thanks again!

Cheers
No, Overdrive is an actual gear, independent of TC lockup.
And I THOUGHT the TC could lock up in 3rd and 2nd, but CJ7-Tim says otherwise

Here's what I would do: get up to speed on the highway such that you are in OD with the TC locked. LIGHTLY TAP the brake pedal and note how many RPM the engine increases then take your foot off the brake and allow the RPM to drop back. Now shift from OD to 3rd and note the RPM. Compare to what happens when you turn the lights on and you should have a better idea what's going on

And yes, I'm assuming that there is a short between the lamp circuit wires and one of the TCU wires. IF it's dropping from OD to 3rd, it's that violet wire.
IF it's the TC unlocking then that would be a white/black wire, BUT, you'd have to interrupt the circuit to unlock the TC, not induce current via a shorted wire...
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Unread 05-19-2013, 06:36 AM   #12
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I think Tim is on to something here. Find where the brake to TCU converter lockup wire is spliced into the chassis wiring. Possibly a poor choice.
Light blue wire with yellow tracer plugs into C10 on the tCU. It is NOT tripped by the brake switch but by a Cruise/Trans switch which is separate from the brake switch.

White one in the photo.
tcu-cc-switch.jpg  
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Unread 05-19-2013, 02:36 PM   #13
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I think Tim is on to something here. Find where the brake to TCU converter lockup wire is spliced into the chassis wiring. Possibly a poor choice.
Light blue wire with yellow tracer plugs into C10 on the tCU. It is NOT tripped by the brake switch but by a Cruise/Trans switch which is separate from the brake switch.

White one in the photo.
Picked up some diodes from RadioShak yesterday. I wasn't able to break into the TCU yet though. I got half way through removing my body lift and broke a fuel line and had to deal with that first.

Thanks again for all the suggestions.
I think you're right about the choice of the wiring being poor. I really hope I can solve this in the next day or two. I picked up 6 diodes so I figure that I can just keep splicing them in until it works haha!

I'll keep you posted.

Cheers
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Unread 05-19-2013, 03:20 PM   #14
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How about getting the dedicated switch for the TCU?
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