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AW4 No 4th

G

godplayer

NAXJA Forum User
Location
Fredericton, NB
About a month ago I had no 4th gear/overdrive but it returned when i shut off and restarted the Jeep. Well today I lost 4th again but it hasn't come back. No engine light. What the heck??
 
Just a thought...

Try cleaning your Neutral Safety Starting Switch. It can cause some weird things to happen.

Do a search, theyre is a very good write up on taking one apart and cleaning it.

HTH
Paul
 
How can the brake light switch cause the problem? How do I check that? My brake light switch makes a clicking noise when i push the brake....it always has since i bought the Jeep.
 
godplayer said:
How can the brake light switch cause the problem? How do I check that? My brake light switch makes a clicking noise when i push the brake....it always has since i bought the Jeep.
Click to expand...
Whenever you touch the brakes it'll unlock the torque converter so even though you're in 4th, maybe you think its in 3rd because its not what you're used to. I rarely see 4th gear unlocked. I just had this problem the other day and it went away over time. I still have to tweak my NSS to get it working perfect but its tough in the cold...
 
How much rpm variation with there be from unlocked to locked torque converter? It is fine with the TCM disconnected and it ran fine since I got the Jeep in september up until about a month ago.
 
I'm not sure on the newer XJs, but on the older Renix ones the brake switch for the TCU is seperate fro the brake light switch. It's white and higer up on the brake pedal. If you have cruise, it also has a vacumn line going into it.
 
godplayer said:
How much rpm variation with there be from unlocked to locked torque converter?
Click to expand...

When you think it's locked, and you're at a steady speed, give it a little gas - enough that your rpms should go up a couple hundred. IF they go up, it's unlocked, if they don't immediately go up, but the engine sounds likeit's under a bit more load and they go up as you speed up, it's locked.
 
lawsoncl said:
I'm not sure on the newer XJs, but on the older Renix ones the brake switch for the TCU is seperate fro the brake light switch. It's white and higer up on the brake pedal. If you have cruise, it also has a vacumn line going into it.
Click to expand...

My cruise works fine. Would my cruise screw up if it was messed up?
 
The brake switch is only going to kick you out of lock. You go into lock in 3rd or 4th, depending on speed and load.

You should be able to have 1-2, 3, and D or 4th manually, but you won't have lock. That's TCU driven only.

You can backprobe the TCU connector with a voltmeter and watch any of the outputs and the brake switch. Mine was going out of lock erratically, and I confirmed it wasn't the brake switch that way, and was in fact a flakey TPS. I would check that the signals to the trans from the TCU are according to what should be, then check the connections at the trans.

IF I remember, both signals to the trans for gear selection (there's 2) are the same in OD.

One day soon I'm going to hook up 12v LEDs on a little panel and run them to all these points, relays, etc. Any digital on/off signal (won't work with analog sensors). Then I can SEE what's going on if or when something acts weird on the road.

I just hope I don't get hypnotized from all the pretty twinkling lights... ;)
 
had a similar problem a while back with mine ( 96 xj ).
it would kick out of lock up after driving for a while @ highway speeds . finally one day it just went to neutral while slowing for a stop .
at the time i did not have a tach to observe rpm's , so i wired in an led to the torque converter feed from the tcu , so i could tell at a glance if it was locked or not .
long story short , it wound up being the turbine output speed sensor .( no diag. available in the fsm )
located under the transfer case shifter bracket on the drivers side , 2 wire white connector ( dealer only around $50 ? it's been a while back ).

i left the led connected , and have never seen it lockup in anything other than 4th gear .
 
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