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torque converter issue (tricky issue need some gear heads)

black_goose

NAXJA Forum User
Location
Houston Texas
Hey guys,

i'm having some trouble with my transmission/torque converter. I'm just gonna summerize my problem so I don't waste any of yalls time.

98 Cherokee (4.0)
163,000 miles (still running strong)
242 transfer case
AW4 Transmission

A while back my transmission wouldn't lock up in overdrive, and sometimes it wouldn't switch in over drive, basically i'll be pulling 2200 rpms at 60mph.

It threw 2 codes: p0700, p0743
0743: torque convert clutch solenoid.

I did my research (extensively) and found out it could be a number of things.

So here's all i did to it (prior to the problem) and after i had the problem:

- NSS (was changed before the problem happened [i think], bought a 150 aftermarket one on ebay)

- Speed sensor changed

- TPS, IAC both changed (TPS was changed twice just in case)

- transmission fluid drained and replaced twice with (i'm pretty sure) Dextron3/Mercon, no discoloration was noted, fluid checked out fine.

-OHMS checked on all solenoids, they read within the range of 11-14 OHMS +/-. (I didn't check it myself personally, transmission shop said they read well).

- no bad or irregular shavings of any sort in the transmission.

now here are the only 3 things i havn't done yet, the last one of course being my last option considering its the most expensive:

- transmission flush (under the pressure of the transmission pump, i don't agree to power flushes)

- TCU replacement (not sure how to exactly do that, but i assumed if the OHMS on the solenoids were good than the TCU should be fine)

-a new Torque Convert (my last culprit).

here are my concerns:

Now it only does it sometimes (which makes me assume it could be electrical)

Something i thought was strange was when i let off the gas when lock up is working, the rpms fall to 1000, and jump up to 1200 and then gos back down to 1000, is it supposed to do that? :confused:

I think it might be doing it when it heats up (not sure).

i was in a couple of front end collisions and thought that maybe my transmission lines were pinched but the transmission shop told me that the fluid checked out fine.

i'm stumped guys, any help would be appreciated
 
There is a switch (or two, cruise?) in the brake area, way up under the dash that is tripped when you hit the brakes to tell the TCU to unlock the TC. It can be removed, disasembled and cleaned, and reinstalled.
 
not that this helps in the least but i too have somewhat same issue. Mine is a 98, 4.0, aw4. mine throws code 700 and 740. very intermittent and very annoying. I have noticed that it doesn't matter hot or cold on mine. While driving down the highway and i notice it is not locking up, if i quickly move the shifter from D to N and back to D it does the lock up as it should. also while it is working just fine and i have to downshift to pass someone or speed up it will sometimes not lock back up. The brake switch works properly on mine and i have checked and replaced the NSS. my last resort was TCU as i checked everything else. i hope someone has some info to clear something up here... good luck man
 
its amazing that even trans shops don't know what they're doing. just because a solenoid resistance is in spec when you test it doesn't mean its ok. there's more than just ohms, and you aren't testing the solenoid during operation ( you can't).
 
Something i thought was strange was when i let off the gas when lock up is working, the rpms fall to 1000, and jump up to 1200 and then gos back down to 1000, is it supposed to do that?

Yes, that is normal. Its the trans computer unlocking the t/c when it saw you let off the throttle. It should also unlock if you reach over with your left foot and tap the brake pedal while cruising.
 
DementedXJ, I've noticed while I was doing my research that this happens mostly on 97-99 Cherokees, which stumps me.

I'm going to replace my TC solenoid anyway regardless. Is there a way to check if the wiring is to the tcu? Or do I have to figure it out after I replace it?

Saudade: thanks do much for tha link dude, I it's full of detail and I don't see how I missed it.

I just hope it the solenoid and not the wiring to the solenoid.
 
DementedXJ, I've noticed while I was doing my research that this happens mostly on 97-99 Cherokees, which stumps me.

I'm going to replace my TC solenoid anyway regardless. Is there a way to check if the wiring is to the tcu? Or do I have to figure it out after I replace it?

Saudade: thanks do much for tha link dude, I it's full of detail and I don't see how I missed it.

I just hope it the solenoid and not the wiring to the solenoid.

I would dig around with a meter, through the wiring, the switches, like the cruise and brake switch, NSS, and wiring before I started spending any money. Not sure why you can't test a solenoid with hot wires from the battery?

I am between Hobby Airport and Pasadena.
 
not that this helps in the least but i too have somewhat same issue. Mine is a 98, 4.0, aw4. mine throws code 700 and 740. very intermittent and very annoying. I have noticed that it doesn't matter hot or cold on mine. While driving down the highway and i notice it is not locking up, if i quickly move the shifter from D to N and back to D it does the lock up as it should. also while it is working just fine and i have to downshift to pass someone or speed up it will sometimes not lock back up. The brake switch works properly on mine and i have checked and replaced the NSS. my last resort was TCU as i checked everything else. i hope someone has some info to clear something up here... good luck man

How do you know if it is locking up?
 
DementedXJ, I've noticed while I was doing my research that this happens mostly on 97-99 Cherokees, which stumps me.

I'm going to replace my TC solenoid anyway regardless. Is there a way to check if the wiring is to the tcu? Or do I have to figure it out after I replace it?

Saudade: thanks do much for tha link dude, I it's full of detail and I don't see how I missed it.

I just hope it the solenoid and not the wiring to the solenoid.

Checking the solenoid resistance by meauring at the tcu connector should check the wiring as well. It can also be done without dropping the pan off the tranny. Usually you start at the tcu and if the resistance is too high or reads shorted, then you'd pull the pan and measure directly at the solenoid. Normally, if the solenoid resistance is within the spec then solenoid is good but there are those rare occasions.
 
Are you checking the VOLTAGE that the solenoids should be getting? Their resistance can be perfect, but without the correct voltage they may not operate or operate correctly.

Is the TCU included in the PCM on the 98? If not, unplug the TCU and drive it shifting manually to see if the problem is electrical or hydraulic/mechanical.

I have read on here of some Slush-box drivers wiring in a toggle switch for the TC lockup so they can use it while rock crawling, so it appears you can energize that solenoid with BAT.
 
How do you know if it is locking up?

if you watch the rpm's you can tell when it locks up. if you pay attention to the shifting you can see once it is in OD it will drop one more time, which is the TC lock up. as well as when it locks up in D when driving slower speeds
 
Are you checking the VOLTAGE that the solenoids should be getting? Their resistance can be perfect, but without the correct voltage they may not operate or operate correctly.

Is the TCU included in the PCM on the 98? If not, unplug the TCU and drive it shifting manually to see if the problem is electrical or hydraulic/mechanical.

I have read on here of some Slush-box drivers wiring in a toggle switch for the TC lockup so they can use it while rock crawling, so it appears you can energize that solenoid with BAT.


the tc is only triggered electricly so pulling the TCU will not help diagnose the non lock up.

The only things that determine torque converter lock up are the TCU, TPS, brake switch and the vehicle speed sensor.

which from that you could assume that the only thing that would keep the tc from locking up would be a failure in the TCU, a bad tps ( which should have thrown a tps code) a bad speed sensor ( which should also throw a code as well as mess with speedometer) a faulty or sticking switch on the brake pedal (i would assume would cause brake lights to not function correctly unless they are seperate switches) and then finally the actual solenoid.

from all that i am still highly confused on how if i quickly shift from OD to N to OD that it locks up just fine. leads me to think maybe it is the TCU or the solenoid
 
could the adjustment of the NSS be a culprit?

dementedXJ: thanks, i'll check the OHMS of the solenoid from the TCU, and have the brake switch checked out.

anyone know exactly what the OHMS should read? should the vehicle be running when i'm checking it from the TCU?

11-14 OHMS right?

ecomike: i'm in the spring area (north side just before the woodlands)
 
if you watch the rpm's you can tell when it locks up. if you pay attention to the shifting you can see once it is in OD it will drop one more time, which is the TC lock up. as well as when it locks up in D when driving slower speeds

That is what I once thought. I finally pulled a tap off the TCU to an LED light so I could tell which was which. Mine almost allways locks up while in 2nd or 3rd, never in OD, and it will cycle off, then on, when it downshifts at WOT, but stays locked as it up shifts back from 2-3-OD. It is always locked up by the time I reach OD. This is with my 87 Renix, but I assume the later models follow the same pattern.
 
That is what I once thought. I finally pulled a tap off the TCU to an LED light so I could tell which was which. Mine almost allways locks up while in 2nd or 3rd, never in OD, and it will cycle off, then on, when it downshifts at WOT, but stays locked as it up shifts back from 2-3-OD. It is always locked up by the time I reach OD. This is with my 87 Renix, but I assume the later models follow the same pattern.


how did it feel like when you were accelerating while it was locked?

did it feel sluggish? like you lost some power?
 
how did it feel like when you were accelerating while it was locked?

did it feel sluggish? like you lost some power?

Maybe a little, yes, becuase it is locked. You get more torque (feel more power) at higher rpms. When it is locked the rpms don't kick up as high on mild acceleration.

However, it unlocks if you step on the gas enough, like WOT, to drop to a lower gear.

Also at WOT, it will not lock up, until late in 3rd or OD depending on when you back off the gas.
 
That is what I once thought. I finally pulled a tap off the TCU to an LED light so I could tell which was which. Mine almost allways locks up while in 2nd or 3rd, never in OD, and it will cycle off, then on, when it downshifts at WOT, but stays locked as it up shifts back from 2-3-OD. It is always locked up by the time I reach OD. This is with my 87 Renix, but I assume the later models follow the same pattern.

I paid attention while driving my 89 today. If the power/comfort switch is in comfort, the t/c stays locked up 2->3->4th. In power mode it unlocks at each shift.
 
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