Possible AW4 slipping isssue.

Hey guys,

Jeep:

99 XJ Stock except 3in lift with transfercase drop(1in.)
236k miles



This past weekend I was on the highway doing about 65-70mph when my transmission slipped(Or so I think) I lost power and had to let go of the gas for a few seconds to get power back. I immediately slowed to 55-60 but sure enough a few minutes later it happened again. I have been looking online everywhere to look for answers but can't find any.

Here is what I have done:

I replaced 2 quarts of transmission fluid(Dex) (drain, fill, drive for each quart). The old fluid looked more like soy sauce. I also bough this used at about 232k miles and now have about 236k. I'm assuming the prior owner(s) didn't even look at the tranny.

After replacing the fluid I took it for another drive and it didn't slip while on the highway but there was a low but sort of loud humming that I hadn't heard before. After going on the highway though I was on a side street doing no more than 35 when it happened again. The next and last time I have had this happen was when I was at a stop light on a smallish hill. The light turned green and I went to go but it slipped and I didn't have power or very little power for a few seconds.

I have read online that these issues could be anything from the transmission to the cat. I also know that the AW4 is a tank so I'm not sure what could be going on. I sure hope this is electrical or the cat but I am just not sure.

Any help would be great! Thanks in advanced.

Try overfilling the trans by about a pint. An AW4 that is getting weak will sometimes run fine if it's slightly overfilled, it's happened to me.

Try adjusting the throttle valve cable, too. http://www.naxja.org/forum/showthread.php?t=1015963

Also try disconnecting the TCU and driving it like that. You won't have torque converter lockup and second gear will be missing, but you'll get 1st gear in 1-2, 3rd in 3, and OD in Drive. The CEL will be on. If it acts up while the TCU is unplugged, you have a mechanical or hydraulic problem, if it does not, you have an electrical problem, though I can't think of any electrical problem that would cause this.

edit: if you do end up needing an AW4 I have one in great shape that will fit your year and am in central mass. I bought it years ago for my 96 XJ before I knew anything about AW4s and shelved it when I discovered it wasn't compatible with my year. PM me or find me on facebook if so, same username.

Start with the fluid, just like you're doing. Mine was pretty dark when I first got it, and would slip and surge when I hooked up anything to tow; only towing or with a few hundred pounds of gear. After about 6 months worth of fluid changing (swapping 2 quarts every 4 weeks) it drives great. I still get a hiccup when towing sometimes, but it drives great otherwise. I do think this is a culprit for my low gas mileage too...

kastein said:

Try overfilling the trans by about a pint. An AW4 that is getting weak will sometimes run fine if it's slightly overfilled, it's happened to me.

Try adjusting the throttle valve cable, too. http://www.naxja.org/forum/showthread.php?t=1015963

Also try disconnecting the TCU and driving it like that. You won't have torque converter lockup and second gear will be missing, but you'll get 1st gear in 1-2, 3rd in 3, and OD in Drive. The CEL will be on. If it acts up while the TCU is unplugged, you have a mechanical or hydraulic problem, if it does not, you have an electrical problem, though I can't think of any electrical problem that would cause this.

edit: if you do end up needing an AW4 I have one in great shape that will fit your year and am in central mass. I bought it years ago for my 96 XJ before I knew anything about AW4s and shelved it when I discovered it wasn't compatible with my year. PM me or find me on facebook if so, same username.

Click to expand...

Thanks for the advice! I'll try what you suggested and if I do need to replace it I'll be sure to get in contact with you. Thanks again!

kastein said:

Try overfilling the trans by about a pint. An AW4 that is getting weak will sometimes run fine if it's slightly overfilled, it's happened to me.

Try adjusting the throttle valve cable, too. http://www.naxja.org/forum/showthread.php?t=1015963

Also try disconnecting the TCU and driving it like that. You won't have torque converter lockup and second gear will be missing, but you'll get 1st gear in 1-2, 3rd in 3, and OD in Drive. The CEL will be on. If it acts up while the TCU is unplugged, you have a mechanical or hydraulic problem, if it does not, you have an electrical problem, though I can't think of any electrical problem that would cause this.

edit: if you do end up needing an AW4 I have one in great shape that will fit your year and am in central mass. I bought it years ago for my 96 XJ before I knew anything about AW4s and shelved it when I discovered it wasn't compatible with my year. PM me or find me on facebook if so, same username.

Click to expand...

After adjusting the throttle valve cable and driving it, nothing was different. I didn't get any slipping but there was still an odd humming. So I disconnected the TCU and took it for a spin. A quarter mile in I come to a stop. The engine then goes down to 300-400 rpm I switch it to neutral to see if that would help but it continued. Eventually it fixed itself but lasted about 4-5 seconds. That is the same amount of time the tranny would slip for too.

One more thing to note; while on the highway with the TCU disconnected it would go to 60mph and the tach would be at about 2k. With the TCU connected and at 60mph it would be around 1k or lower. The engine would sound like it was struggling to go further if I put my foot on the gas.

That makes sense - with the tq unlocked it will rev higher at highway speed.

The rest I can't explain, I am pretty weak on how the hydraulics of these transmissions function.