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Torque Converter Staying Locked

S

streetxj

NAXJA Forum User
Location
Pembroke Pines, FL
Hello everyone. My 1996 jeep cherokee 4.0 automatic (Aisin Warner) has a recent issue. It shifts up fine 1 to 2, 2 to 3, then 3 to 4 and the torque converter locks-up at 43-44 mph. But, once it locks it stays locked even if I let off the accelerator and coast to into the 20-30 mph range. Until it almost reaches 1000 rpm coming to a stop, it wouldn't unlock. Once it gets to that point, it unlocks and takes-off normally. Even if I would slow down to 30 mph and give it gas, it BANGS and accelerates very slowly (locked-up). If I floor it, it unlocks. Not too long ago I heard and felt a click sound(ratchet sound) from under the hood when I gave the truck sudden acceleration and felt it through the accelerator pedal. I thought it was an intake backfire, but I'm thinking that my transmission cable adjuster might be worn and getting out of adjustment on it's own. Also, it doesn't unlock when I press the brake pedal. It used to, but now not even doing that unlocks it. Seems to be worse each time I drive it. I would like to hear different opinions about the possible causes of this problem.
 
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If you're going to replace the TCC solenoid, you might consider replacing the 1-2 and 2-3 solenoid as well. They should all be the same age and I wouldn't want to crack the pan more than once.

You can also pull the TCM connector under the dash and ohm check the solenoid to see if it's in spec for resistance. BTW, the TCC solenoid is going bad on my 98 with 164k. When it gets hot it goes out of spec for resistance and throws a DTC. I want to say spec for the solenoids is around 13-18 ohms, but I could be mistaken. Are you getting a MIL? If you're TCC is locked on, does the Jeep stall or nearly die when coming to a stop?
 
My jeep doesn't stall or bog. It just unlocks at the last minute right above 1000 rpms. I've just replaced the solenoids 4 months back. I've installed junkyard OEM 1996 jeep cherokee TPS from ebay (it was tested) and it worked perfectly fine and it even ran a bit better than the new Omix-Ada (supposedly Mopar) TPS sensor. Before reinstalling the omix-ada TPS that I had put away in the glove compartment, it had the same problem, but it only did it once and then it would act normal again. After changing back to the Omix Ada TPS it got gradually worse. Maybe I should change the TPS again back to the old OEM junkyard one to see if it gets better. If it does improve, then I know that it's the TPS.
 
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brake switch, and associated wiring?
 
Just to cross the "Is" and dot the "Ts", reset the PCM. Torque converter lockup as well as the shift points are controlled by the PCM.

The code for the TC is in the sections labeled "Shift/Lock Schedule". This section of the code defines the following parameters:
WOT Governor Curve Cold
WOT Governor Curve
Unlock for 4th Gear Closed Throttle
Unlock for 3rd Gear Closed Throttle
Relock for 4th Gear Closed Throttle
Relock for 3rd Gear Closed Throttle
Min Throttle Position for 3-4 Shift
Min Throttle Position for 2-3 Shift
Min Throttle Position for 1-2 Shift
Max Throttle Position for 3-4 Shift
Max Throttle Position for 2-3 Shift
Max Throttle Position for 1-2 Shift
4th Gear Torque Converter Unlock Curve
4th Gear Torque Converter Lock Curve
3rd Gear Torque Converter Unlock Curve
3rd Gear Torque Converter Lock Curve
3-4 Shift Schedule

The Section also contains the following parameters:
Maximum WOT Shift Engine RPM Target = 4850
Minimum WOT Shift Engine RPM Target = 4750
Throttle Detent High Limit = 5
Throttle Detent Low Limit = 5
WOT Shift Engine RPM Target = 4800

The lock/unlock parameters for the TC are based off of the OSS_RPM. This is the Output Shaft Speed Sensor located in the transmission.

So... It may be possible that the speed sensor itself may be at fault but one would expect a MIL (CEL) event to trigger.

The point I am attempting to make here is, that contrary to popular belief, the TCM serves mainly as a coil driver for the transmission solenoids and it is the interface for the OSS/PCM relationship. Note that the late model XJs have an ISS added to the transmission.
 
That's great info. Where is it from? Can it be changed?
 
All of the parameters can be changed and what I posted is the "stock tune" for a 1998 XJ with a 4 litre engine. This is a direct readout of my PCM's coding.

What I have for hardware and software is not cheap and so will not be of any large interest to most folk from a "must have" view point.

Not to hijack (much) this thread but there is an interesting parameter buried in the code. It is:
Aspiration Type = 0

There is a very large implication here and once I have attended the programming class (also not cheap...) I will have a better handle on things, I have changed all of my shift points however to take better advantage of the supercharger. There is absolutely no need to run the engine up to 4700 RPM before the upshift. Not when you are shoving 8 pounds of boost (@6,500' altitude = 9.6lbs boost at sea level).

Makes for an interesting drive as I experiment to find the sweet spots per gear change...
 
OGS, please take this as the compliment I intend it as:
You are quite possibly the biggest car-geek I've run across.
 
I will not deny it. As some of you know, I grew up in the house of an "Original Hot Rodder". My Dad was stuffing big motors into little cars from before WWII. I started doing this stuff, actively, around 1960.

My Brother, who is 10 years older than me so he and God are pretty close in age... Still builds power and will be building until he is put into the ground.

We just can not help it. In many ways, it is sort of like an addiction.

My Dad showed me photos of the Marmon V16 he and his Brother stuffed into a Model A. Of course, you had to sit in the back seat in order to drive it but, Hey! It worked...

After WWII (1948), we moved to the San Francisco Bay Area. Sunnyvale to be precise. Good country in which to build. Leastways, it was back then... Left the State in '71.
 
My old man got introduced to hot rodding by a bunch of vets who moved into his neighborhood - he'd been building go karts with lawn mower engines and terrorizing the local neighborhood but these guys showed up chopped, dropped, louvered & with nasty Flatheads in them, he was a convert. Built a few in his days, mostly frankenstein engines. Like a Pontiac 455 that was in his '70 LeMans - used Cadillac MPFI injection. 12 MPG or so but it'd tow the boat at 80+ with plenty of power to spare.
 
My first "official" build was a 1940 Ford Woody Wagon. The three of us (my Dad, Brother and I) swapped out the early flathead V8 for a late model (better engine by far) and then sat a supercharger on top of it.

This was 1960... Sleepers were our specialty and I still build them today. One reason I have a supercharger on my XJ...
 
O-Gauge Steamer said:
Just to cross the "Is" and dot the "Ts", reset the PCM. Torque converter lockup as well as the shift points are controlled by the PCM.

The code for the TC is in the sections labeled "Shift/Lock Schedule". This section of the code defines the following parameters:
WOT Governor Curve Cold
WOT Governor Curve
Unlock for 4th Gear Closed Throttle
Unlock for 3rd Gear Closed Throttle
Relock for 4th Gear Closed Throttle
Relock for 3rd Gear Closed Throttle
Min Throttle Position for 3-4 Shift
Min Throttle Position for 2-3 Shift
Min Throttle Position for 1-2 Shift
Max Throttle Position for 3-4 Shift
Max Throttle Position for 2-3 Shift
Max Throttle Position for 1-2 Shift
4th Gear Torque Converter Unlock Curve
4th Gear Torque Converter Lock Curve
3rd Gear Torque Converter Unlock Curve
3rd Gear Torque Converter Lock Curve
3-4 Shift Schedule

The Section also contains the following parameters:
Maximum WOT Shift Engine RPM Target = 4850
Minimum WOT Shift Engine RPM Target = 4750
Throttle Detent High Limit = 5
Throttle Detent Low Limit = 5
WOT Shift Engine RPM Target = 4800

The lock/unlock parameters for the TC are based off of the OSS_RPM. This is the Output Shaft Speed Sensor located in the transmission.

So... It may be possible that the speed sensor itself may be at fault but one would expect a MIL (CEL) event to trigger.

The point I am attempting to make here is, that contrary to popular belief, the TCM serves mainly as a coil driver for the transmission solenoids and it is the interface for the OSS/PCM relationship. Note that the late model XJs have an ISS added to the transmission.
Click to expand...


I think the 96' ECU (or PCM) does not communicate with the TCU. So I don't think any sensor relating to the transmission would set off the check engine light. Thanks for the info. :) The transmission also stays in low gear until I almost reach full-stop. I don't feel or hear down-shift. So I definitely think that it's the VSS sensor. Here's a quote from another forum: "there is a speed sensor on the transmission it tells the tcu how fast the trans is going mine would drop into low at speed and stay there didn't slip". It definitely matches my symptom.
 
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Actually, it does. There are a number of issues that you can have that will not trip a MIL event. If you would like to prove the communication, just unplug the TCU. It should generate a fault. If it does not, I would really like to know as that would be flying in the face of the documentation I have.

I am always open to learning something new and/or exciting...

As to what the Computer is called... Most everyone in the world call them an Engine Control Unit. Chrysler calls them Powertrain Control Modules. And whereas our JTEC and JTEC+ PCMs do have some limited Powertrain Control (witness the transmission parameters) the 2005 and up are truly Powertrain Controllers as those deal with everything including hte lockers in the axles if so equipped.

Ford calls them (least ways in my Wife's 96 Bronco...) EEC. Go figure that one.

Jeep
Truck
Engine
Controller

So, yes, Chrysler is schizophrenic. The actual box is a "controller" but it is called a "Module". Figure that one too. I just gave up and accepted the insanity...
 
O-Gauge Steamer said:
Actually, it does. There are a number of issues that you can have that will not trip a MIL event. If you would like to prove the communication, just unplug the TCU. It should generate a fault. If it does not, I would really like to know as that would be flying in the face of the documentation I have.

I am always open to learning something new and/or exciting...

As to what the Computer is called... Most everyone in the world call them an Engine Control Unit. Chrysler calls them Powertrain Control Modules. And whereas our JTEC and JTEC+ PCMs do have some limited Powertrain Control (witness the transmission parameters) the 2005 and up are truly Powertrain Controllers as those deal with everything including hte lockers in the axles if so equipped.

Ford calls them (least ways in my Wife's 96 Bronco...) EEC. Go figure that one.

Jeep
Truck
Engine
Controller

So, yes, Chrysler is schizophrenic. The actual box is a "controller" but it is called a "Module". Figure that one too. I just gave up and accepted the insanity...
Click to expand...

Cool. :) Yeah, the ford OBD-II computers are called EEC-V. I believe that's the one in your wife's 96' Bronco. The OBD-1 computers like the ones in the foxbody 87-93 EFI mustangs are EEC-IV. The mustangs began using the EEC-V computers in 1994 when the Sn-95 platform first came out.
 
Well, it would be too easy if everyone used the same terminology.

But, back on point, I would reset the PCM before anything else. Not saying that it will definitely kill this problem but it will remove a variable.

Just disconnect the negative post of the battery and wait a few minutes. This will restore the default settings in the PCM.

You eat an elephant one bite at a time....
 
O-Gauge Steamer said:
Well, it would be too easy if everyone used the same terminology.

But, back on point, I would reset the PCM before anything else. Not saying that it will definitely kill this problem but it will remove a variable.

Just disconnect the negative post of the battery and wait a few minutes. This will restore the default settings in the PCM.

You eat an elephant one bite at a time....
Click to expand...


I'll do that. Thanks :) Anyways, the speed sensor is the original one and it has 161,000 miles on it. Napa has the Echlin replacement for 32 bucks and it's located on the route my dad takes from work. So might as well replace that. He'll avoid having to take another trip by doing that too. It is 15-20 minutes from my house. I'll disconnect the negative terminal, then replace the sensor. Once I'm done, I'll reconnect the negative cable to the battery.
 
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First, I disconnected the negative battery terminal and left it unplugged for 5 minutes with the driver side door open. I've also noticed that the trans kick-down cable was not adjusted properly, so I re-adjusted it. After that, my dad and I took it for a test drive. It was still doing the same thing. It would stay in overdrive with the torque converter locked while coasting to a stop with the foot off the accelerator. The only way it would unlock and downshift is when my dad moved the shifter into 3rd gear (drive) and back into overdrive. Once we got home, he took the newer TPS off and re-installed the OEM factory junkyard TPS. He also unplugged and re-plugged the wire harness plugs that are clustered together on the passenger side of the engine, behind the transmission dip stick tube. The Vehicle Speed Sensor was also changed. It still had the original one and it had a small hair-line crack over it. My dad took it out for a test drive again after re-flashing the PCM and it performed flawlessly. It unlocked as soon as he took his foot off the accelerator and downshifted properly on it's own. :)
 
streetxj said:
First, I disconnected the negative battery terminal and left it unplugged for 5 minutes with the driver side door open. I've also noticed that the trans kick-down cable was not adjusted properly, so I re-adjusted it. After that, my dad and I took it for a test drive. It was still doing the same thing. It would stay in overdrive with the torque converter locked while coasting to a stop with the foot off the accelerator. The only way it would unlock and downshift is when my dad moved the shifter into 3rd gear (drive) and back into overdrive. Once we got home, he took the newer TPS off and re-installed the OEM factory junkyard TPS. He also unplugged and re-plugged the wire harness plugs that are clustered together on the passenger side of the engine, behind the transmission dip stick tube. The Vehicle Speed Sensor was also changed. It still had the original one and it had a small hair-line crack over it. My dad took it out for a test drive again after re-flashing the PCM and it performed flawlessly. It unlocked as soon as he took his foot off the accelerator and downshifted properly on it's own. :)
Click to expand...


Did you change the VSS on the transfer case that feeds the speedometer, or the output speed sensor on the back on the transmission that feeds the TCM? Just curious, because I'm chasing my own issue and think it might be related to the output speed sensor but really have no idea how to get at it without dropping the transfer case.
 
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