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aw4 in YJ issues

bestos

NAXJA Forum User
Location
MD
Hello

I was recommended to check in this forum. I have a 91 YJ with an AW4 conversion. Guy did it for me 5 years ago. My problem is now, the transmission is not acting correctly.

For 2 days it will shift fine from 1,2,3,4 with lockup. Then i start the vehicle, put it in D, and it stays in 4th. I can manually shift to 3 and its in 3rd, and manually shift to 1-2 and its in first.

There are only 4 wires that control it from my research. TPS signal, TPS ground, 12V battery, GND, and (12) 12V ignitions. When the vehicle was working properly, the TPS signal checked out at 0.8V to 3.8V. and both battery, ignition and gnd all good.

Yesterday it went into the mode where it does not shift. I checked the voltages again. TPS voltages to computer are same, and so is GND, batt and ignition.

I have replaced the TPS and i have two TCU and both exhibit the same random "limp mode". I cannot pull codes as this is not a cherokee.

The only other input to the TCU is the Transmission speed sensor (NOT vehicle sensor in TCase). could a bad transmission speed sensor there causing my random issues? This is not spliced like the TPS or GND or 12V signals. This is just transmission to the computer.

The transmission does feel kind of clunky when you move the shifter to DRIVE from park. The solenoids obviously work when selecting 1-2, 3, and 4. I need help. I am trying to avoid a RAD design shifter and want to get this thing right. Would hate to have RAD or go back to manual.
 
Have you tested the power and grounds when it's acting up? How did you test them? If the TCM is not working you will still get manual 1, 3 and 4 with no lock up even if the solenoids are not powered.

If you really want to load a power or ground circuit I like to use a sealed beam headlight. If it comes on bright you know it's all good. It sounds more like an intermittent connection issue. Also try searching for the aw4 thread by kastein here. Lots of good info in there.
 
I test the ground and power by pulling the computer and testing it through the pins. when it is not having a problem and when it is, both times the 12+ and ignition 12V and ground check out. although the battery is 12.5V an ignition is 12.1.
 
Yes, a failing vss can cause weird shifting issues. That guy is just some sort of hall effect sensor that produces pulses based on the speed of the output shaft. Check that sensor out, and verify that your getting a signal from it when the shaft turns. Your 12v power look fine.
 
To be clear my mention of vss was inaccurate. I am referring to the transmission output speed sensor. It is on the adapter between the transfer case and trans. That feller is in charge of telling the tcu how fast the output shaft of the trans is spinning.
 
i saw online that sensor is a biatch to get too. how do i test that sensor? will it output a signal if the computer is unplugged? I have to be moving to get a signal, unless i put it on jack stands i guess. what voltage range am i looking for? in all my online research, no one has given any measurements for that one.
 
Normally a failed output speed sensor will cause the trans to be stuck in 1st not 4th. I suspect one of two things - your NSS is faulty or your TCU is faulty or not receiving power. I would suspect TPS but you already tested it.
 
Kastein,

the NSS is not hooked up to anything in my swap to my knowlege ( i can start vehicle in D), but i will do anything, how do i test it?

I will follow the harness again and check where the guy wired the 12+ and 12 switched. I can only see the TPS wires and Gnd.
 
update everyone - it was the TPS. I changed it like i said above - i guess the computer was still adjusting it for the next day or so. now that it is settled, i have never had a problem yet. just wanted to give an update in case anyone ever had this problem. I am running the newer computer as well just because.
 
edit, the first computer was the jeep computer, the 2nd computer reference was the transmission ECU.
 
Glad to hear it's working well!
 
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