I could use a little education on how the torque converter is controlled.

Long story short, I've owned my truck for about a year and a half and it has always been very erratic in how it shifts. Sometimes (especially early in the morning), it shifts as smooth as silk. Other times it slams into gear and wants to lug the engine down.

I do have AE, and can clearly see that when it's shifting smoothly, it shifts 1,2,3,4, TC lock. When the shifting is poor, it tends to shift 1,2, TC lock, 3,4. The TC stays locked until I hit the brakes. Sometimes it even stays locked when I downshift (resulting in a pretty rough shift).
I live in a hilly part of the world (east TN), and I find that when driving lightly, the tranny will hold a gear with the TC locked even at low RPM's (below 1100) and will lug the engine. The only way to get it to downshift is to floor it. Shouldn't the TC unlock in these situations?

What I really want to understand is what controls the TC lock? Is it computer driven, valve body, RPM, or tranny pressure?

The PO did have the trans rebuilt by a questionable shop prior to my ownership. It also had a rebuilt TC installed.

My suspicion is that it either has a plugged cooler (restricting flow), damaged wiring, bad TC, or a mis-installed shift kit. But I'm not going to shotgun parts at it without fully understanding the system. I'm actually a pretty good wrench, I just don't typically mess with automatic transmissions (and computer controlled ones at that).

Are there things with AE that will help me diagnose what's going on here? So far I can see the TC slippage, and commanded lock. It seems to be doing what it's told to do. Are there other trans parameters to monitor?

Thanks for any and all help

Dave
2000 CC 4x4
225,000 miles

 

Did you happen to install LED tail lights recently?
You might try monitoring your brake pedal on AE and see if the value changes when you depress the pedal. If not, then your PCM won't know you are applying the brakes and will leave the TC locked.

If your TC is locking and unlocking when the PCM tells it to, then I'd say your trans is ok and the problem is somewhere else.

 

Thanks Greg,

I don't have LED tail lights (or any others for that matter). I did follow up on something I read last year and checked my tail light bulbs to make sure the correct bulbs were installled. Actually found that my third brake light was out. Unfortunatly, replacing it didn't help.

I'll add the brake switch monitoring to the screen and see if I can find any correlation.

Thanks for the input,

Dave

 

The torque converter clutch is controlled by the PCM. It looks at input from several sensors to determine when to lock and unlock the converter.

 

Besides the brake signal....what other systems does the PCM monitor to control the TC? Is it a giant list?
(trying to learn a little more about this myself...)

 

i would assume vehicle speed and RPM are both worked into the equation with the brake pedal position. Trans oil temp as well.

 

Accelerator pedal position
Road speed
Transmission temperature
Current gear
Brake switch status

 

I think the proper shift sequence is 1st, 2nd, 3rd, TC lock, 4th.

Under light load on an incline, my truck will not downshift either. It feels odd compared to a gasser, but it really doesn't need to.

 

Depends on the PCM code.

Ideally, your sequence is preferred, but some don't do it that way.

 

Thanks for all the input guys!

I did a little data logging last night and this morning.

I do have one code that has been around since I bought the truck, P1876-transfer case 2wd solenoid circuit failure. I always assumed it had something to do with the PO installing manual hubs. Maybe it's related??

I monitored RPM, Brake pedal, TC slip, TC Clutch modulated, TCC inernal circuit modulated, Shift solenoid 1, 2, and 3, and accelerator pedal position. I didn’t monitor road speed, or trans temperature (is that picked up by AE)?

One of the odd things I noticed is that Shift solenoid 3 never shows engaged, sometimes both 1 and 2 are active at the same time but I’d assume that’s just part of the shift strategy.

Modulation seems to be all or nothing. It seems to go from 0 to 100% almost immediately.

There is no reading from TC internal circuit monitoring (assume it’s not used).

This morning it seemed to shift well and smoothly and the TC seemed to lock after the 3-4 shift. Last night I think it was locking right after the 1-2 shift and didn’t unlock until the brake was depressed.
I wouldn’t be as concerned if it was consistent all the time but the varying smoothness of the shifting has to mean something is screwed up (from smooth as silk to a solid bang).

I can live with the fact that they don’t downshift when lightly loaded on a hill to a point. It seems like it will just chug along with no ability to accelerate without an intentional downshift and then it takes off., almost too aggressively.

Bear in mind that this is my first diesel (though I’ve had it for a year and a half), so if I’m just expecting it to perform in a way it’s not designed to then I need to adjust. But I’m really not being overly sensitive here, it’s a pig on a slight incline without flooring it.

Thanks for the education so far but obviously I’m looking for a little more…… I understand that the TC lock is triggered by the computer but how is it performed? I would assume that a valve controls fluid pressure or something. Is that contained in the valve body? If someone (like a lousy transmission shop) were to mess around with the valve body is this something that could be affected?

Thanks Guys,
Dave

 

Shift solenoid 3 isn't used on the 4R100 (I think it may be used on the TorqueShift models though...).

MPH can be read by AE.
Trans temp can also be monitored if you connect at 2000 model or later. (for whatever reason, connecting at 1999 doesn't give you the trans temp selection)

I think the TC is either locked or unlocked. I don't think there is any in between. Best as I can tell, it appears the input shaft might have a passage that provides fluid pressure to the TC to activate the clutch mechanism inside. If that is true, then I presume there is a solenoid/valve somewhere in the transmission body that is controlled by the PCM whenever it wants the TC to lock. I've noticed when the TC locks, it doesn't really hit hard. It seems like it initially grabs with about half force and then grips more firmly about half a second later. (could just be my perception though...). On my truck, the TC locks immediately after the trans shifts into 4th gear.

When I encounter an incline and give it a little bit of throttle, the TC will stay locked as long as I am not giving it too much throttle to maintain speed. If I press harder on the pedal, then the TC unlocks and the trans downshifts in most cases.

What size tires are you running? If you aren't running the original size, have you used AE to correct your mph?

 

I did a little more logging at luch. Of course when you hook the computer up, the truck behaves it's self so I'm not sure that I'll have anything useful.

I did select trans temp, it appears that I selected volts though. My truck is a 2000 so it appears to be working. It's on an inverse scale, i.e. the higher the temp the lower the voltage (makes sense).

As far as how the TC locks up, mine doesn't seem very progressive, it's more like dumping the clutch on a standard (maybe that's the problem).

My truck reacts the same on a slight incline but I don't think the TC is unlocking before down shifiting. It just slams into 3rd....

I'd really like to understand the control mechanism, it must be a solinoid of some sort. May be the root of the problem.

Thanks for the help
Dave

 

Sorry I ment to add that the tires are 285x75x16 (about 31.5") and I have made the correction thru AE.

Dave

 

Yes, the trans temp volts is an inverted scale. I have a converter file that I can send you if you would like. PM me with your e-mail and I'll forward that file to you. If you connected as a 2000 model year, then you should have Trans Fluid Temp as one of your choices as well. If not, then you might need to upgrade your software and/or firmware. Do you have the Proline connector? Here is a link to a thread from when I updated last. (contains some words of caution...)
https://www.ford-trucks.com/forums/9...ate-issue.html

Even with the software updated....I still can not see trans temp (in degrees) on AE if I connect at 1999 model year. If I lie and say that it's a 2000 model, then I can see trans temp in degrees and it's accurate. Weird.

Unfortunately I've reached the limit of my knowledge regarding how the TC actually operates. Hopefully Mark, Cody or someone else will explain with more specifics.

 

The root is in the programming. The way you describe what's going on perfectly describes transmission strategies by certain PCM codes.

It also perfectly describes some tuning characteristics.... namely a PMT1 style shifting with 4-3 downshifting enabled, and a bit of extra fueling on the bottom end.

Do you have a chip or programmer installed?