AW4 Torque Converter is not unlocking. Please help.

I have a 97 Cherokee with the automatic.
It shifts good and has been regularly serviced.
However, once the converter locks in 3rd or 4th (approx 45mph)
it will not unlock when trying to accelerate.
This makes it seem sluggish (especially when pulling my camping trailer)

For example: Driving on level ground at 50mph. Press the gas a bit to
speed up and it sloowwwly accelerates (like a manual tranny in top gear).
Feed in some more gas and it will drop down to 3rd gear without the
converter ever unlocking in 4th.

However, if I gently press the brake (just enought to activate the brake switch)
it unlocks and accelerates better when giving it some gas.
So I believe that shows that the solenoid that controls the converter lock/unlock is
working ok.

I installed and set up a new TPS thinking that would be the problem after reading
some other posts (usually about the LACK of getting into lock)
This did not fix it.

Does this mean the TCU is faulty?
Are there any other things I can check myself without being at the mercy
of a tranny shop??

Thanks for any help.

Don't go to a tranny shop. They are usually clueless about electronics and would probably try to sell you a new torque converter and a $700 bill. I just read a post about someone whom the stealership wanted to charge $1200 for a rebuilt tranny - the problem was a blown fuse.

If it's unlocking when you tap the brake, the t/c and solenoids are fine and it's on the electrical side of the house. The symptoms certainly sound like a bad TPS sensor, bad TPS wiring, or wiring to the TCU from the engine computer. On the HO engines and later, the TCU gets its throttle position signal from the engine computer instead of a secondary output on the TPS sensor. If you have a meter, I'd probe the TPS signal at the TCU and make sure it's changing between roughly 0-5 volts as you press the accelerator (key on, engine off). My 95 FSM says its pin D2 and my 98 FSM says pin 17. They agree that it's an orange wire with dark blue stripe.

If it's not wiring or a bad sensor, then it may be the TCU itself although it's rare that one is actually bad. You can usually find a replacement TCU on eBay fairly cheap. The extra ones I sell usually go for $30-50.

$1200 for an AW4 at the dealer is cheap,$1200 for a fuse is alot.

Just makes me wonder how many sleazy shops tell people they are rebuilding the tranny when they are just fixing minor problems like a bad solenoid. It's unfortunate that the vast majority of the public isn't mechanically inclined and wouldn't know any better.

Most of the AW4's I see come from other shops right after being rebuilt a couple times by guys that don't know what's up. I don't think I've ever
had to rebuild an earlier AW4, just the later 2wds that tear up the planets.
There are good trans shops out there just like there are good General
repair shops. Always ask to see your trans when it's apart on the bench.

Thanks for the responses!

I see that the TPS itself is different for the newer Cherokees, as mine
has only a 3 wire plug, but the diagrams I read online show a 4 wire TPS.

I checked the voltage when I set up the new TPS.
It ranges from .85 millivolts at idle to 3.9v at wide open throttle.
I also checked the TPS I was replacing and it was at
.83ma to 3.88 volts.

I will try to find the TCU and check the input voltage from the TPS
as you suggested lawsoncl.

So if the wiring checks out ok, it is most likely the TCU?
Could it also be the engine computer itself?

Also, I am assuming that the converter does indeed unlock and the revs
jump a couple of hundred RPM under mild to moderate acceleration with the AW4?
I am assuming mine is not functioning properly based on other slushboxes I
have driven.

Thanks.

This makes it seem sluggish (especially when pulling my camping trailer)

Click to expand...

Could be it never locked up in the first palce when pulling your camper?

Oh it locks for sure when towing.
I watch the tach and temps constantly when towing as we
have some big mountains around here.

Yeah, the TPS sensor on the newer HO engines is a single plug and non-adjustable like the older Renix's. I have not driven a 97, si I can't say how easily they unlock the t/c. I would think you wouldn't want it to keep unlokcing on mild acceleration as that just adds heat.