Coopenhagen23

Hey everyone. The title says it all, but I will give a brief run down in the history of the jeep. 98 XJ, 4.0, AW4 transmission...After many years of sitting on jack stands for an axle build idea that ended up getting scrapped, I decided to revive the jeep and get it mobile again. To get it moving again it needed the following...
- Stock axles, steering, and suspension with the exception of a small lift
- New fuel pump (replaced entire sending unit)
- Cleaned out gas tank
- Plugs, wires, coil, cap, & rotor
- radiator and fan
- Fluids (motor, diff, trans, coolant)
- brakes

Taking it around town and general driving, it runs awesome. Some buddies and I decided to go on a few wheeling trips recently and in the beginning of these trips it runs great. after a while of it being in 4wd (high or low) it starts to stall out. 99% of the time this happens on downhill events, at low speed, and during braking. it also happens if I'm on a downhill incline and I put it in reverse. Initially I was thinking fuel issue, but if it was a fuel issue this would happen with on-highway driving as well in 2wd. After testing a couple different theories, I believe that the low speed crawling is heating up the transmission and possibly causing the torque converter to not function properly. Imagine driving a manual downhill, at low speed, and hitting the brake with out pushing in the clutch, and the engine is fighting to keep idling. It acts just like that. Once I get to level ground it runs fine. I can even put in neutral and go downhill slowly and it will keep itself running. I've read that the TPS and CPS can influence the transmission drivability, but I'm not familiar with the relationship between the different sensors and the transmission. Any help would be appreciated!

Thanks all!

dave1123

The only thing that comes to mind is somehow the torque converter clutch is getting engaged when it shouldn't be. I may be totally out of the box, but that's all I can think of at the moment. I've been staring at your post long enough for the monitor to have shut down twice already and my brain hurts. Let me go burn some more brain cells.....

lawsoncl

Or the CPS is getting hot and failing. The normal failure mode for the t/c lockup solenoid is failing to engage, and not staying locked.

dave1123

If the solenoid port is plugged, it won't vent the fluid. But why does to only do it when submerged? (all the fluid rushing to the front of the pan)

Ah! Wait! What fluid did you use in the trans? DexIII/Merc I hope. ATF+4 can cause problems in an AW4.

Coopenhagen23

How exactly does the CPS control the torque converter lock?

Coopenhagen23

If it was a vent plug, you would think it would happen on other braking events during highway driving (slowing down for a stop sign or red light). I did put ATF in it.... I was not aware that was an issue for these jeeps? What exactly does the AW4's not like about ATF?

awg

It doesnt

If your torque convertor is locked up, the vehicle will bog down and stall when you come to a halt

The TCM controls the TC solenoid, so either the fault is intermittent, or their is some other cause (such as a failing sensor etc cutting the engine)

Coopenhagen23

It is definitely not intermittent. It's is only at low speed and once I've been in 4wd for awhile and once it begins, it is very easy to replicate.

awg

its possible to backprobe the harness at the TCM or connector in the engine bay and detect whether a 12V signal is being sent to the TC solenoid, (and check its resistance) they can fail in more than one way, to my understanding they can jam when they get very hot

I recently had to replace a failed No2 solenoid (open circuit, no 2nd or 3rd)

Its up to you whether you think its worth drop the pan to inspect and replace it

Coopenhagen23

Just bumping to see if any one else may have some ideas. I’m gonna try and spend some time working on it this weekend. Will most likely start with CPS since it’s the easiest, and probably cheapest, to swap out.

Roler

CPS is worth a try, since it will eventually fail somewhere during its life
When mine went bad, I had backfiring/stalling, under specific conditions, like right hand turn, going slightly uphill.
Also during driving it would backfire at times, especially accelerating and once put in Neutral (even on the go) that would immediately disappear and it would rev fine.

Those things all resolved after changing my CPS.

If you want to check if its 4WD related, try to replicate the same situation where it stalls (downhill, low speed, braking) but do this in 2WD, Just as a test. Takes that out of the equation.
If it would heat up the trans too much to cause those issues, you would expect it to continue for a bit longer and not disappear as soon as you hit levelground (the trans would still have the same temp, I'd think)

The other thing that came to mind, you saying 99% of the time it happens under those specific conditions, is that you will likely not apply throttle in those situations; in that case the IAC (Idle Air Control valve) is responsible for the air "transport". After you finish the 4WD sections, does it idle normal?
Together with the throttle body plate, it might be good to take both off and give them a good clean.

Just an idea to see if it makes any difference. These are relatively easy to do and good maintenance anyway for future reference.

Roler

How is this coming coming along?

Any updates yet?

cruiser54

2 things.

Perform Tip 10 at www.cruiser54.com.

Have you ever thoroughly cleaned the throttle body and IAC?

Coopenhagen23

I've replaced the Crank Position Sensor and the Cam Sensor(pick up coil)... I haven't had a chance to take it out on the trails yet to see if it fixed anything.. So far no issues around town, but like I said before - casual driving was never an issue.

Hoping to get it out soon though... I will keep everyone posted.

Coopenhagen23

Thanks for the link. A lot of great information in there.

I have not cleaned the throttle body or the IAC. I'm sure it needs it.