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Reverse problems

Pgw1995

NAXJA Forum User
Location
Arkansas
Ok guys please help. Ok, took your advice. I adjusted TV cable, no change, when I pushed it back it stayed at full throttle, with slack so it could have been broke or really stretched so I put a new on, no change. So I changed fluid, because I didn’t know what previous owner used. Flushed 3gal of Dex through it before I thought it was clean enough, oh ya, new filter. Now reverse is worse!! All forward is still fine. Reverse now will not engage unless you give it some throttle ( I’m not going to hammer it) just easy on throttle and it will move but not good. With TCM unplugged it shifts forward gears fine but no improvement with reverse. I haven’t had this Jeep long and have found many wiring issues (I am an electrician by trade) the only codes I get is P0700 which is pretty random and the P0720. Still diagnosing the output speed sensor. Sensor is working TCM isn’t reading it. Trying to line that out. I wouldn’t think the speed sensor would affect reverse. This is a 95 tranny and 4.0 in a 98 Xj. Just found that out when I was trying to purchase a speed sensor (before I found out how to test it) the reverse issue is only at motor operating temperature, when cold it kicks right into reverse? (going to install a temp gauge on tranny when my cooler gets here. This Jeep is pretty much stock. It does have 6 1/2” lift, 35” tires, 373 gears (was the way I bought it) (next project is 456 gears) once I get this reverse issue figured out. I have a line pressure gauge coming in also (which I will say reverse is probably low). Long story short, time for another tranny? Also rebuild this one or junk yard tranny that I can test drive? Thanks in advance. Need some advice. Confused after all this work it is worse?
 
Ok guys please help. Ok, took your advice. I adjusted TV cable, no change, when I pushed it back it stayed at full throttle, with slack so it could have been broke or really stretched so I put a new on, no change. So I changed fluid, because I didn’t know what previous owner used. Flushed 3gal of Dex through it before I thought it was clean enough, oh ya, new filter. Now reverse is worse!! All forward is still fine. Reverse now will not engage unless you give it some throttle ( I’m not going to hammer it) just easy on throttle and it will move but not good. With TCM unplugged it shifts forward gears fine but no improvement with reverse. I haven’t had this Jeep long and have found many wiring issues (I am an electrician by trade) the only codes I get is P0700 which is pretty random and the P0720. Still diagnosing the output speed sensor. Sensor is working TCM isn’t reading it. Trying to line that out. I wouldn’t think the speed sensor would affect reverse. This is a 95 tranny and 4.0 in a 98 Xj. Just found that out when I was trying to purchase a speed sensor (before I found out how to test it) the reverse issue is only at motor operating temperature, when cold it kicks right into reverse? (going to install a temp gauge on tranny when my cooler gets here. This Jeep is pretty much stock. It does have 6 1/2” lift, 35” tires, 373 gears (was the way I bought it) (next project is 456 gears) once I get this reverse issue figured out. I have a line pressure gauge coming in also (which I will say reverse is probably low). Long story short, time for another tranny? Also rebuild this one or junk yard tranny that I can test drive? Thanks in advance. Need some advice. Confused after all this work it is worse? Oh ya, I have tested all solenoids and TPS. Guess I’ll check TCM for power and grounding issues, but all forward gears are good.
 
Ok guys please help. Ok, took your advice. I adjusted TV cable, no change, when I pushed it back it stayed at full throttle, with slack so it could have been broke or really stretched so I put a new on, no change. So I changed fluid, because I didn’t know what previous owner used. Flushed 3gal of Dex through it before I thought it was clean enough, oh ya, new filter. Now reverse is worse!! All forward is still fine. Reverse now will not engage unless you give it some throttle ( I’m not going to hammer it) just easy on throttle and it will move but not good. With TCM unplugged it shifts forward gears fine but no improvement with reverse. I haven’t had this Jeep long and have found many wiring issues (I am an electrician by trade) the only codes I get is P0700 which is pretty random and the P0720. Still diagnosing the output speed sensor. Sensor is working TCM isn’t reading it. Trying to line that out. I wouldn’t think the speed sensor would affect reverse. This is a 95 tranny and 4.0 in a 98 Xj. Just found that out when I was trying to purchase a speed sensor (before I found out how to test it) the reverse issue is only at motor operating temperature, when cold it kicks right into reverse? (going to install a temp gauge on tranny when my cooler gets here. This Jeep is pretty much stock. It does have 6 1/2” lift, 35” tires, 373 gears (was the way I bought it) (next project is 456 gears) once I get this reverse issue figured out. I have a line pressure gauge coming in also (which I will say reverse is probably low). Long story short, time for another tranny? Also rebuild this one or junk yard tranny that I can test drive? Thanks in advance. Need some advice. Confused after all this work and it is worse. I also checked all the solenoids and TPS.

I just read a thread about the transfer case causing reverse slack. Is this possible? While I had my Jeep in my shop I decided to go ahead and do a complete fluid and oil change on everything, since I just got it. Opened up transfer case and it was totally dry (not a drop)
 
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Yes, I have seen that. I have searched, and searched for diagnostic tips over and over again. I think I have tried everything except changing every sensor and just put in a hole new harness. If there is any advice on what to try that maybe I haven’t. Please open up!!
 
So you read the AW-4 swap thread and have the correct AW-4 for your 1998, or made the modifications necessary to make the 1995 AW-4 function in a 1998 ?

You have found the AW-4 Service Manual, and have performed the diagnostic tests ?

Have you solved the P0720 ?
 
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Unfortunately, problems with reverse are usually mechanical as none of the solenoids are activated. The P720 code though indicates you do also have some sort of electrical issue. In addition to the connector at the trans computer, there are a couple of connectors on the passenger side of the firewall in the engine bay that you should clean. Also clean the ground point at the dipstick mounting bolt. A lot of sensors get grounded there.


This is a 95 tranny and 4.0 in a 98 Xj


How did you resolve the issue with a 1995 tranny in a 1998 vehicle? The 95 trans is not going to have the input speed sensor that the 98 trans computer wants. Could be the reason you're getting the P720?

https://www.naxja.org/forum/showthread.php?t=1053970
 
Yes, have done the test, no haven’t verified that I have the right TCU. Going out right now to check it out. Is there a noticeable difference in the 98 TCU and the earlier ones? Or do I have to pull it?


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Unfortunately, problems with reverse are usually mechanical as none of the solenoids are activated. The P720 code though indicates you do also have some sort of electrical issue. In addition to the connector at the trans computer, there are a couple of connectors on the passenger side of the firewall in the engine bay that you should clean. Also clean the ground point at the dipstick mounting bolt. A lot of sensors get grounded there.





How did you resolve the issue with a 1995 tranny in a 1998 vehicle? The 95 trans is not going to have the input speed sensor that the 98 trans computer wants. Could be the reason you're getting the P720?

https://www.naxja.org/forum/showthread.php?t=1053970



I didn’t know it was a 95 until I started trying to find a speed sensor. That is when I realized the swap but still didn’t know the exact year so I called the previous owner. He said the motor and transmission both are out of a 95. Maybe time for another call and ask about the TCU


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I didn’t know it was a 95 until I started trying to find a speed sensor. That is when I realized the swap but still didn’t know the exact year so I called the previous owner. He said the motor and transmission both are out of a 95. Maybe time for another call and ask about the TCU

Yes, even with the TCU unplugged it still takes a while to engage into reverse. But only at operating temperature. Cold, it kicks right in.




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A 1998 trans will have the extra input speed sensor on the front drivers side. The output speeds sensor going to pulse at 4x per rev, versus 1x for the 1995. I think the connectors on the firewall also changed, but not positive about that. 1998 at least adds two wires for the front speed sensor. It is possible to swap parts between the years to fix the rear sensor issue. If it really is a 1995 trans connected to a 1998 tcu, it's not going to upshift properly as it'll think you're moving 1/4th as fast.



From memory, I believe the connector on the 1998-2001 trans computer is white, 1992-1995 is green, and 1989-91 is gray. The wiring harness side of the connector is color coded the same and they are keyed so they only plug into the correct tcu. (I think 98 also changed the pin layout?). The 98-01 mounting bracket looks like bat wings, and previous have more normal looking flanges. If they did swap TCUs, it would require some modification.
 
A 1998 trans will have the extra input speed sensor on the front drivers side. The output speeds sensor going to pulse at 4x per rev, versus 1x for the 1995. I think the connectors on the firewall also changed, but not positive about that. 1998 at least adds two wires for the front speed sensor. It is possible to swap parts between the years to fix the rear sensor issue. If it really is a 1995 trans connected to a 1998 tcu, it's not going to upshift properly as it'll think you're moving 1/4th as fast.



From memory, I believe the connector on the 1998-2001 trans computer is white, 1992-1995 is green, and 1989-91 is gray. The wiring harness side of the connector is color coded the same and they are keyed so they only plug into the correct tcu. (I think 98 also changed the pin layout?). The 98-01 mounting bracket looks like bat wings, and previous have more normal looking flanges. If they did swap TCUs, it would require some modification.



Ok, now I’m more confused. I have a grey plug (89-91)? Bat style TCU bracket (98-01), and a 95 engine/transmission????
 
Ok, now I’m more confused. I have a grey plug (89-91)? Bat style TCU bracket (98-01), and a 95 engine/transmission????



68fbcae0675808c5ec85b4d08a1eb232.jpg
 
Yes, that's a 98 model year TCU, and I believe 97H means manufactured Dec 1997. I've heard a 97 TCU will work and would be the simplest solution. I just looked at the 97 and 98 manuals and confirmed the tcu connector pinouts are the same, minus the input sensor on the 97. You might have to trim or modify the connector if the keying is different but should otherwise plug right in.
 
Yes, that's a 98 model year TCU, and I believe 97H means manufactured Dec 1997. I've heard a 97 TCU will work and would be the simplest solution. I just looked at the 97 and 98 manuals and confirmed the tcu connector pinouts are the same, minus the input sensor on the 97. You might have to trim or modify the connector if the keying is different but should otherwise plug right in.



I would like to ask you something else before I purchase a 97 TCU ( I have dumped a lot already, and no better ) I understand that the 98 TCU doesn’t understand what is going on, and will cause my CEL, but would it not recognizing the output shaft speed sensor make the tranny take awhile to engage reverse (at idle) (can give some throttle and it will speed engagement up) forward seems to hit on time? Or do you think I probably have a tranny laying down? Don’t want to get a 97 TCU, loose the CEL and still not have a good reverse. It gets really bad when it warms up.
 
The TCU shouldn't affect reverse. In fact, you should be able to unplug the TCU entirely and have reverse work normally. Were you able to adjust the new throttle-trans cable? Engagement in the forward gears seems normal?

The AW4 service manual says for slow Reverse engagement (> 1.5 seconds):
- Shift linakge misadjusted (can't see that being temp dependant)
- Line pressure low (throttle cable, wrong fluid, overheating...)
- First/Reverse brake worn
- Overdrive Clutch worn or damaged.

The AW4 service manual says for slow Drive engagement (>1.2 seconds):
- Shift linakge misadjusted
- Line pressure low
- Forward clutch worn
- Overdrive Clutch worn or damaged.
 
The TCU shouldn't affect reverse. In fact, you should be able to unplug the TCU entirely and have reverse work normally. Were you able to adjust the new throttle-trans cable? Engagement in the forward gears seems normal?

The AW4 service manual says for slow Reverse engagement (> 1.5 seconds):
- Shift linakge misadjusted (can't see that being temp dependant)
- Line pressure low (throttle cable, wrong fluid, overheating...)
- First/Reverse brake worn
- Overdrive Clutch worn or damaged.

The AW4 service manual says for slow Drive engagement (>1.2 seconds):
- Shift linakge misadjusted
- Line pressure low
- Forward clutch worn
- Overdrive Clutch worn or damaged.



The new shift linkage acted the same as my old one. Pushed it in eased pedal to WOT and it snapped out maybe 1 click. Test drove air wouldn’t shift at all. So I started manually adjusting it. Shifts good in forward gears. But still hesitating reverse engagement. Unplugged TCU haven’t drove it enough yet to see how reverse does. It has always engaged good when cold, when the Jeep gets up to operating temperature is when it starts acting up. I wonder if the 35” tires with 3.73 gears is overheating the transmission? It never messes up in forward gears though. 4.56 gears is my next project. I have found another transmission for it. Need to sell this one but don’t know what to tell people. If it’s good or not. I have a cooler coming in tomorrow. I’ll install it and see if it helps. I understand my CEL but don’t understand the reverse yet.🤔 forward is great. I would think if it’s a heat issue I would see it in all positions. But it doesn’t act up till it gets warmed up (only reverse)


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