1990 torque converter lockup issue

ok guys I am brand spanking new to the world of Jeep ownership so I apologize ahead of time for my ignorance of common issues, common acronyms, system names, and anything else that may hinder communication here. I'm short on knowledge but willing to learn.
Disclaimer over- here's my problem:
A couple of weeks ago I bought a 1990 Cherokee Laredo, part time 4x4, auto, 160k miles. Seems to be in decent shape overall. I drove it back and forth to work all last week and had no real issues so I decided to take it to the beach this past weekend. Everything went great, we romped around in the beach sand with it, was able to park right next to the water and set up camp, so far it was doing all of the things that I bought it to do. The trouble started on the way home.
First thing I noticed - and I had kinda noticed this during the week- while holding in-town speeds (for instance ~40 MPH) which requires very little gas pedal input, the torque converter would cycle through lock and unlock after very slight changes to the gas pedal input. I hope I'm explaining that clearly... picture holding a steady speed on a city street, and lifting your foot just slightly as you are gradually getting closer to the car travelling in front of you. When I would do that the TC would unlock, even though the actual commanded change was very slight. Add just a bit of pedal more to accelerate and the TC would lock up again. Once you got up to highway speeds, it would stay locked up and seem to behave normal.
Are you with me so far?
Now again, I have no experience with Jeep systems but I do have some experience with other brand automotive systems so this is where my thought process went: Once I noticed the odd behavior, the first thing I thought of was the throttle position signal not being read correctly by the transmission computer, in other words, if the computer thought you had lifted your foot completely off the gas and was coasting, it would unlock the TC to reduce engine RPM during coasting.
Other than that, everything seemed OK. But wait, it gets better.
So now we're on the interstate on our way home and buzzing along at 75 MPH. I noticed a couple of hiccups spaced several miles apart, barely perceptible. Then suddenly there was a hiccup and the engine RPM went up by about 200 RPM. We didn't lose any speed and kept chugging along but the engine was now running faster to keep the same speed. I decided the TC must have unlocked for some reason, but we're on the open road with wife and kids so I kept going, now with one eye on the gages. After a few more miles I noticed that the temp gage was slowly climbing, which made sense compared to my diagnosis because if the TC is not locked up it will generate more heat in the transmission, which would be transferred to the coolant. I dropped speed to 65 MPH, but it continued to climb very slowly.
When it got to the 210° mark I got off the highway. At the bottom of the exit ramp I stopped, turned, and listened carefully to the transmission shift: 1st, 2nd, 3rd, 4th, aaaaand lockup. So it decided to work again after coming to a stop.
I pulled into a gas station and as soon as I came to a stop the steam starts pouring out. Pop the hood and it's boiling the coolant out from under the cap on the resevoir tank. I punted at that point and had it towed home.
SO- let's be clear on the sequence. Until this episode the temp gage has always been very cool, well below the 210° mark even on these hot days with the AC running. Very clearly there was some sort of transmission issue first, leading to the boil over.
Any ideas on where to start? What to test? common issues with these vehicles?

Well, which came first? The chicken or the egg?

Actually, did the transmission overheat the cooling system, or did the cooling system overheat the transmission?

As it is new-to-you, I would start with an inspection/service of the cooling system. I would buy some commercial (like Prestone) aggressive flush, the kind you put in and drive 500 miles or so--not the 15 minute wuss flush. After you run the good flush--following manufacturer's directions, make sure you also flush the heater core, here is one recommended method found in another thread:

"I called the Stealership to see if they would tell me what they did. AND THEY TOLD ME !


HEATER CORE FLUSH:
They disconnected the top and the bottom heater hoses at the block- where the Tstat is. (Not the fire wall)
- Connected the gargen hose to the top hose and flush it through the heater core and out the bottom hose.
- Then connected the garden hose to the bottom hose - flushing the heater core backwards out the top hose.


Connect everything back up."


and:



"BLOCK FLUSH:
They said to flush the block - they removed the Tstat
- disconnected the Bottom heater hose
- Connect the garden hose to it.
- turn on the water
- flush the heater core into the block and out through where the hose was connected.




Connect everything back up.


- remove the top hose
- connect your garden hose to that hose
- flush through the Heater core and through the block and out where the hose was connected to.


REPLACE YOUR THERMOSTAT


YOU'RE DONE"


Then, inspect all your hoses, and make sure the bottom radiator hose either has the OEM support spring inside (still available at the dealership) or is of a high quality manufacture (i.e., Gates) so it will not collapse, which they have a tendency to do.


Speaking of thermostats, you should use a good quality 195 degree thermostat. Also, the 1990 came OEM with a "closed" cooling system (no cap on the radiator) and a pressure bottle instead of an overflow bottle. The closed system must be burped, or trapped air will play havoc with your cooling. First, drill two small holes in the thermostat flange, one at the top and one at the bottom. They need to be in from the outer flange edge so that they are not covered by the gasket when installed. Install the Thermostat with the holes at 12 and 6 o'clock. Very important--make sure the block and thermostat housing surfaces are very clean. Any left over old gasket/sealer and you will have a leak and be doing the job again.


Ok, system is flushed, new 195 degree thermostat, new hoses(?), now lets talk about your turtle/football/pressure bottle. These age and develop cracks, and the hose attachment is prone to breaking off. They are expensive for the OEM Mopar bottle, like $50+. You can buy cheaper (Chinese) bottles, and they work fine just as long as you throw the cap that comes with them in the trash and buy an OEM cap at the dealership. Actually, you can make the crummy Chinese cap work by putting a worm-type hose clamp around it so it will stay on the bottle.


You need a 50/50 mix of quality coolant. The best way to put the coolant in is to remove the upper radiator hose from the thermostat housing and pour the coolant in there.


Now, to Burp. Probably best for you is to park the XJ nose-down. Then, engine off of course, at the driver's side rear of the head is the temperature gauge sending unit. You will have to remove it to let the air out of the engine, and you can add more coolant to displace the air at the pressure bottle.


Now, almost done. Check your fan clutch. When the engine is hot turn it off and then see if the fan clutch is fully engaged. If you can turn it, it needs replacing. I personally recommend upgrading to the ZJ (grand cherokee) HD fan clutch, NAPA part number 272310, $44, and it is a direct fit. There is also a max cool version, but it won't fit. Also, as you have an auto, do you also have a/c? If yes, you have an aux electric fan (efan). I should come on about 215+ degrees, the sensor is in the radiator on the side. It should also come on anytime the a/c is running. Check to see if it is functioning correctly.


Sorry the short reply.

thanks for the detailed reply, I know it takes a lot of effort to type all of that out and I truly appreciate it. The tip about the location of the CTS and using it to burp the system is exactly why I joined up here... it's learning all of these little things about a particular vehicle that add up to being very proficient and keeping it on the road, and I need to start learning all the little things about the XJ.

I could be wrong here, I really could be... but the sequence of events seems to me to very clearly spell out transmission trouble first, leading to the coolant on the ground later. It is of course easier for me to say that having been on the spot rather than reading about it, but I'll elaborate a couple of facts to make my point:

- I just bought the car and started driving it a week ago. My commute is 50 miles each way with mostly highway but some in-town, plus I drove around town on errands and stuff. So, I had put about 400 miles on it before leaving on this trip, and a total of maybe 550 miles before the overheat event.

- the temp had always stayed very low. Not a lot of detail on the factory gage but I'd guess it was hanging around 180° to 190° in all driving conditions

- something was definitely up with the TC lockout behavior from the time I started driving it. The weird in and out of lockup in response to slight changes of throttle at in-town speeds was there from the start although it showed no problems on the open highway. 75 MPH was roughly 2400 RPM when all was well

- finally, I noticed very clearly when the lockup disengaged during the long highway run. I was on alert and watching the dash gages very intently from that point on. At the time it happened, temp was at that same low 180° mark.

- after several miles of elevated RPM, the temp started slowly creeping up.

So to me, the overheat is very definitely a response to a transmission issue. The transmission issue is already there prior to any sign of overheat.

I hope that what I'm trying to express is clearer. I have a tendency to ramble and I know it can be difficult to follow my descriptions, but I appreciate any attempt to help.

Ok. Be sure and test/adjust the TPS, It can play havoc with things.

Also, two links plenty of info on the AW4:

http://www.transonline.com/transdigest/magazines/1997-10/Shift%20Pointers/index.html


http://www.scribd.com/doc/2922823/AW4-manual1

Yes, check the TPS sensor. Also check the sensor on the brake pedal. The trans computer has its own sensor on the brake pedal. They sometimes get gunked up and stop making good contact, which tricks the trans computer into thinking you've applied the brake. The cruise control also connects to this switch, so if you're cruise keeps kicking off this is definitely suspect.

It should be a white and way up near the top of the pedal. The switch can be carefully popped apart and cleaned up.

excellent, I'll check out the web links for the transmission info. I suppose the best way to learn how to test/ adjust the TPS is by buying a service manual? Or does anyone have a link to the procedure on a website?

Welcome to


here is a great link for/on the Renix sensors.
http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

and you have a pm aswell

well for what its worth as far as the kicking in and out at in town speeds dosent seem like a real problem (i thought the lockup happened at 45 mph) so going above and below 45 will cause that. And many here say that running near 210 is normal as the e fan dosent kick on till 215. anyways good luck and welcome

First task should be to inspect the tranny fluid for signs of coolant!

Also check the radiator for signs of tranny fluid.

Replace any bad cooling system parts where it leaked, bottle, bottle cap, hose?

Replace the gauge sensor, it should not have overheated and boiled over at 210 F. Should have made it to 240 to 260 F, unless cap/bottle was bad.

Install a worm gear clamp on the bottle cap (seach words: "Renix worm gear clamp bottle" , this forum).

I would then suggest pressure testing the radiator to see if the tranny cooler tube in the outlet side of the radiator is leaking, but the renix system has no such radiator neck fitting for the tester to attach to. There is a new thread here, where I added a filler neck discussion this week to mine, just for testing the system, pressure testing. More discussion on that later, as that addition requires another addition, so go find that thread if you want to add the filler neck. More details there.

Your lock, unlock, may have been a 3rd to 4th, 4th to 3rd gear shift triggered by a TPS that is going bad. Or a solenoid problem in the tranny, the solenoid that locks the TC, or the second TC brake switch discussed below (white one way up above the brake peddle).

If the fluids got mixed, you have many problems and tasks ahead.

Lastly, the two things, overheating, and the tranny engine rpm shift, TQ....??? issue may not be related. At this point I would not assume anything with out a lot more inspection and data.

Update:

I've figured out why it boiled over at what should have been a safe temperature- the expansion tank cap is indeed NG. It barely sits on there, and if you try to tighten it even a little bit it rolls over the threads and falls off. It says "made in China" on it so I guess somebody changed it at some point and you guys are right... Thanks for the tip. I'll pick one up from the dealership or see if I can find an OEM one in the junkyard this Saturday.

now if I could just figure out the transmission weirdness...

dm440c said:

Update:

I've figured out why it boiled over at what should have been a safe temperature- the expansion tank cap is indeed NG. It barely sits on there, and if you try to tighten it even a little bit it rolls over the threads and falls off. It says "made in China" on it so I guess somebody changed it at some point and you guys are right... Thanks for the tip. I'll pick one up from the dealership or see if I can find an OEM one in the junkyard this Saturday.

now if I could just figure out the transmission weirdness...

Click to expand...

Search for my "Bottle Renix" thread, author Ecomike. Use a worm gear hose clamp on the new cap, read about it in that thread.

dm440c said:

excellent, I'll check out the web links for the transmission info. I suppose the best way to learn how to test/ adjust the TPS is by buying a service manual? Or does anyone have a link to the procedure on a website?

Click to expand...

Google on "AW4 TPS Adjustment". The first hit is the one you want, with a nice walk through and a few pictures.

Note that posting a link to that website (even just to this procedure) will get you red-flagged as the site happens to have other copyrighted materials. See http://www.naxja.org/forum/showthread.php?t=59881 for why we can't link to copyrighted materials.

I tested the TPS and it was OK: 0.950 V with the throttle closed and a smooth transition up to 4.5 V at WOT

...so my transmission issues seem to be caused by something else.

I'm making a list of things wrong with my Jeep as I discover them.

Here's all the intermittent issues:

1) sometimes the starter will not engage in Park and you have to shift to Neutral to start it. Other times it will start in Park. You never know.

2) TC lockup once disengaged completely on a long highway run. Since then has worked ok (other than with respect to issue #1 in the second list below)

3) sometimes hard to start, fires & stalls repeatedly, sometimes you have to feather the gas pedal to keep it running. Most of the time however it starts and idles on its own. You never know.

4) sometimes the idle moves around a lot, gets higher for a while, then goes down several hundred RPM for a while. This is in Park with no A/C, defrost, or any of that stuff on. Sometimes it idles perfect. you never know.

5) sometimes the A/C works, sometimes it doesn't. No discernable pattern of conditions. It's just a roll of the dice whether it will decide to work. You never know.


the following is an issue always (NOT intermittent)

1) torque converter lock-up hunts at speeds between 30 - 50 MPH with light/ steady throttle

2) the little switch for the transmission labeled "Power / Comfort" doesn't seem to do anything

3) cruise control doesn't work

4) shift lever is wierd; you don't have to press the button to pull it out of Park OR to go from Neutral to Reverse, but you do have to press the button to get it in Park.

5) rear wiper doesn't work

6) front wiper switch is crazy, Low is Off, one of the delay settings is Low, High is also Low....? some of the delay settings work.

7) oil pressure gage is pinned at nine million PSI with the engine running

Well your NSS is bad, as seen by not starting sometimes in park. Weather that has anything to do with TC lockup problems, I don't know. Perhaps if it was thinking the shifter is in a position other than 4, or changing positions, it would unlock/lock funny (IIRC the D position = no indication from NSS, so maybe it's switching intermittantly to thinking it's in 3rd, and causing things to happen). It's not a cheap part, which is why I just made a switch to make it think its in R so my backup lights come on, and one for N so I can start it (N and P give the switch the same reading).

And check all your vaccum lines, since your cruise does not work. Conceivably bad lines could impact your idle as well.

My power/comfort switch has long ago quit lighting up, but it still seems rather obvious that it works. It changes shift points a little bit, most noticeably by where it goes into 4th. Of course it does little to actually add power or comfort to the vehicle. The comfort setting is ridiculous, and IMO should not be used, which is most likely why the trans defaults to "power" in later model XJs, having removed the option of switching.

Save yourself some bucks and trouble later down the road by getting rid of the OEM overflow bottle. Go to the junkyard and get a bottle from a mid 90's Mopar. it is shaped different, but when you remove the OEM bottle and its bracket, it bolts right up to the shelf. These bottles are MUCH sturdier and have a REAL radiator cap to hold pressure and releive it if necessary.

NSS can be rebuilt fairly easily and can affect the transmission. A little searching will lead to good links for this. Good place to start.

Common bottle replacement is from an Intrepid.

dm440c said:

I tested the TPS and it was OK: 0.950 V with the throttle closed and a smooth transition up to 4.5 V at WOT

...so my transmission issues seem to be caused by something else.

Click to expand...

.95 V is too high. Should be 0.83 at idle. It is adjustable, but loosening the screws and turning tell it reads 0.83 at idle on the ECU side (the one you did test).

You need to test and post test data on the back side of the TPS, it is the side that speaks directly to the TCU, tansmission Control unit.

tugalo said:

Save yourself some bucks and trouble later down the road by getting rid of the OEM overflow bottle. Go to the junkyard and get a bottle from a mid 90's Mopar. it is shaped different, but when you remove the OEM bottle and its bracket, it bolts right up to the shelf. These bottles are MUCH sturdier and have a REAL radiator cap to hold pressure and releive it if necessary.

Click to expand...

My cousin happens to have a wrecked 2002 Intrepid parts car, I'll take a look at using that. If it doesn't look like it will work I'll make a quick trip to the pick n pull yard and see what I can find from the 90's. Thanks for the tip

Ecomike said:

.95 V is too high. Should be 0.83 at idle. It is adjustable, but loosening the screws and turning tell it reads 0.83 at idle on the ECU side (the one you did test).

You need to test and post test data on the back side of the TPS, it is the side that speaks directly to the TCU, tansmission Control unit.

Click to expand...

ok. The service manual just says "over 200 mV at idle" and since 950 is greater than 200 I concluded it was OK. To test, there were six wires coming out of the TPS... I just probed each one until I found one that changed when the throttle plate was manipulated. The harness is on the front side of the throttle body under the air intake snorkel. Is this not the right place to test?