Torque Converter Not Locking Up When Warm.

S

streetxj

NAXJA Forum User
Location
Pembroke Pines, FL
I've been having this problem for a while. My 1996 jeep cherokee 4.0 still had the original TPS (159,000 miles) and I changed to a duralast one a couple of months back. The torque converter would lock all the time during the first few days then it stopped locking after driving for 10 minutes. Then 5 minutes. I changed the TPS to another duralast and it wouldn't lock-up at all. Then after a while, it started locking-up again, but then when the engine reached around 190 degrees, it would stop locking up. I decided to spend extra $$$ and went with the MOPAR tps sensor. I installed it this past weekend. Well, the truck feels ALOT quicker and throttle response feels MUCH sharper. The torque converter locks-up really well, but when it reaches the 190-195 degree mark, it doesn't lock-up.. I'm basically going 40 to 50 mph (4th gear). When it locks-up completely, going into over drive (4th gear), it stays locked even when I lift my foot off the accelerator (coasting). It would down shift and unlock once it hits near 1000 rpms while braking. This is when the engine temp is around 180 and lower. I would hate to hear that it's the TPS again especially after I bent backwards for the MOPAR. One thing though, like I've mentioned before, it runs a lot better than with the Duralast TPS sensor. I would appreciate any advice and opinions.
 
Actually look up when it's supposed to lock and what the "locking" torque converter actually means. A lot of the times I think you are talking about your tourque converter should not be locking.
 
joejeep92 said:
Actually look up when it's supposed to lock and what the "locking" torque converter actually means. A lot of the times I think you are talking about your tourque converter should not be locking.
Click to expand...


It should be locking all the time. At least my mom's 2000 jeep cherokee does it every time it goes into 4th gear. I was just trying to also include the behavior of when it "does" lock just in case. I apologize for causing any confusion.
 
Any resolution with this issue? I hope you've found your fix, because I've been chasing this similar problem for years and all I ever find are these dead ended posts. :-/
 
On HO-era Jeeps, always check the adjustment of the brake switch on the pedal if you're having problems with the torque converting not locking or acting funny. I've dealt with two rigs where the brake switch being out of adjustment caused the torque converter to unlock randomly while going down the highway, because the switch was "just barely" making contact even though you weren't pressing on the pedal.

The brake switch controls the brake lights, defeats cruise control, and defeats torque converter lockup when pressed.
 
NotMatt said:
On HO-era Jeeps, always check the adjustment of the brake switch on the pedal if you're having problems with the torque converting not locking or acting funny. I've dealt with two rigs where the brake switch being out of adjustment caused the torque converter to unlock randomly while going down the highway, because the switch was "just barely" making contact even though you weren't pressing on the pedal.

The brake switch controls the brake lights, defeats cruise control, and defeats torque converter lockup when pressed.
Click to expand...

Definitely--we see this on all types of vehicles at the shop, it is one of the first things we check.
 
TPS has no effect on TC lock up, unless it is really screwed up bad and bouncing the RPMs up and down wildly enough for the TCU to delay TC lockup.

Other than the obvious common brake switch cause, how old is the Trans fluid?
 
Last edited:
Also... have you checked the adjustment on the Throttle Valve (TV) cable? I'm not sure if this has any input on when the torque converter locks or not, but it's easy to adjust and has been known to cause funky driveability issues. Do a search on here to see how to adjust it.
 
Does your trans needs servicing? If so, I'd pull the pan and measure the resistance of the solenoids. One of the three solenoids controls the TCC (Torque Converter Clutch). All three should be between 11-15 ohms. Your TCC solenoid could be slightly out of range and with heat (heat causes increased resistance) it may malfunction.
 
I hope streetxj found his fix, however I'm going to continue to hijack his thread if he doesn't mind.

I've found write ups on the brake switch, and I've adjusted it as well as replaced it.
I've tried adjusting the TV cable (also from another write up I saw from naxja) and it seemed to self adjust back to what it was, so I believe it's fine. I haven't replaced my tps, but being that it is rare the tc refuses to lock I don't think it is that. (it has been consistently rare since 06)
I have not ohmed out the solenoids, but weebur your suggestion seems to be the only thing I can think of at this point. The added heat is the only time the lockup doesn't happen. Whether it is a solenoid or a damn wire going to it.
The tranny had been rebuilt a couple of times as well as swapped before I had the sense to ask questions a few years ago. Since then I've had fluid flushes about once a year. And even a valve body kit put in. Everything has helped the feel of the tranny, but the inevitable fail to lock up from longer/ hotter driving peaks its ugly head.
I'm half tempted to stick a lamp indicator inline from the tcc to the 3rd solenoid to see if it is getting the signal. At least that way I can isolate the problem being behind all of the sensors.
 
I added a small red LED light to my dash to show TC lockup. I was a huge help in diagnostics, because I could not tell for sure if it was the 2-3, or 3-4 shift or a TC lock up just watching the Tach.
 
TC lockup override switch FTW!
 
My thoughts exactly. It's a bandaid, but since I'm thinking an electrical issue by passing the gripe with a manual switch when needed will be fine.

Or buy another jeep! :idea:
 
Think of it as an upgrade. Work good Offroad also. Enables you to engage tc lockup in any gear.
 
With the vehicle cold check the resistance at the TCU (directly above the drivers right foot. Then check it when its hot and not engaging. Checking at the TCU will allow you to check the solenoid and ALL the wiring to the trans. I have found the problem with these symptoms to be the lock-up solenoid, brake switch or bad wires at the plug near the dipstick. The pins in the connector become corroded. The solenoid starts to die but not completely. The brake switch fails or is out of adjustment.
The test of the lock up is drive at aprox. 50 MPH keeping yourfoot on the gas steady-Tap the brakes and the RPMs should rise 3-400 RPMs.
This is a pain in the ass to diagnosis and repair. Stick with it and you will get it.

Ron
 
Thanks. I tapped the brake and the rpms spiked as expected.

I shot continuity tests through all of my wires from off of the TCC connector to the connector next to the dip stick, and then did a resistance check using the same wire and ground to the tranny pan. The lockup solenoid tests about 11.9-12.1 ohms cold. Once I've been driving her around til it stops locking up again the Ohms are 16.9. Max tolerance is 15 or 16 ohms. I pulled another harness off of a junk yard xj and checked each wire for continuity and resistance. (all check well) My concern lies with the solenoid being bad... again.

I hate to think I'd have to UNmodify my jeep just to save my lock up solenoid from going bad. I did pull a taurus fan as well. If it's the heat that keeps killing my solenoids hopefully that'll help.

Thanks again for all the ideas and help.
 
I've had funky TPS's act up, and other than the idle bouncing while stopped, the next symptom was erratic lock-up of the TC. Also erratic shifting when accelerating from rest. I've had the best luck with 'previously loved' pieces from the yard. I made up a test plug from a junkyard donor, where I cut off a plug, leaving an inch or two of wire. I tinned the ends, and now have a test plug. Using an analog meter with the leads alligator clipped to the test plug, you can cycle it, looking for any drop-outs as you sweep the TPS through its range. The center lead is the common on the swiper, and the two outer leads are either end of the windings. It's best to find a known-good vehicle, to get target values, then test your TPS' against the values, to see which ones most closely match the target. I had six to choose from, and unbelievably, the readings were all over the place. I chose the one with the closest readings, and magically it 'cured' all my problems.

The TPS's are all the same from '91 till about midway through '96 (the 'Classic' model '96 Cherokees actually have a '97 harness in them, and the TPS plug is different). ZJ 4.0 from '93 through '96 is also a donor source. The TPS's are the same, but as you get into the later years, it's the plug that differs.

The OP mentions that he's got a '96, and this year was recalled for a 're-flash' of the ECU and a check for a broken cat. I debated whether or not to have it done, and, unfortunately I did. That's when the problems started...
 
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