A4LD w/ no torque converter lockup at Altitude?

[explorerjoe]

So here is a question for all the A4LD guru's out there. I leave Phoenix for Colorado and find my T.C won't lock up north of Sedona. I am in the mountains, stock gears now running 33's (just a day old). Figured its a final drive ratio thing slowed down to keep it cool and pushed on. Hit 40 east and it locks up about 10 miles east of Flagstaff. I get 20 mile east of Gallup New Mexico and it won't lock up again. To make a long story short head back to Phoenix and the damn things locks right up about 20 west of gallup. quiets working just before flagstaff and I see it engage at multiple point passing through the mountains. Essentisally the T.C did not lock up in all the same locals. Now I am curious. Turns out when my GPS is showing over 4400' my T.C doesnt' engage. I even turned around, when I was 4400' above sea level my T.C won't lock up. Could this be caused by the Vacuum Modulator? Obvioulsy in the mountains i will be running lower manifold pressures? Here in Phoenix i have no problems, it works 100% of the time. The trans was rebuilt using a new Modulator, and a transpro A4ld jr kit. It also has a "Heavy Duty Torque Converter" designed for hard use. It has braized fins and a "better clutch". Is it possible the vacume modulator is the villian? What does it do exactly? I have confirmed the the fluid level is full..
Thanks,
Joe

 

[Opera House]

At higher altitudes

and with those tires the throttle is open a lot more. The TPS tells the computer that the engine must be at a higher load at that rpm. I just changed the VSS gear in my 97. This was to correct the speedometer which was 10% fast even though the odometer was correct. I now have a lot of OD shifting in the mountains that I never had before.

 

[MrShorty]

As Opera House alluded, the problem is almost certainly a computer control issue, since the TCC is controled by the computer. As mentioned, the primary inputs used to determine when to lockup are the TPS and the VSS. If the ECT shows too hot, the computer will disengage the TCC. I don't know if the baro sensor figures into it. I assume the CEL is off, but I wonder if the computer would put out any codes.

 

[explorerjoe]

Excellent, I was unaware of a speed sensor being figured in on my 94. I thought that was used only by the trasfer shift computer. I knew that the computer controled lockup, but never thought of the increased TPS due to the higher load. I know that I have a Mechanical speedo, will changing the gear to correct for the obvious speedo error also correct the speed sensor error? I pulled the error codes and got my usual Camshaft Positon Sensor, no other code was recorded.
Thanks for the help.

Joe

 

[AlaskanJack]

Ah now this is interesting, I have been having problems that just seem to overwhelm me. My O/D has not been working and I can feel no torque converter locking up even coasting downhill or when I let off the gas at 55mph. I did just discover that the VSS was disconnected at the t-case, but it didn't make any changes when plugged in. I will clean out the plug since it was really dirty. For info I am running 35's and my speedo reads correct and my 4x4 won't engage. I have a new computer coming for the rear compartment since my tests indicated it was bad and the motor tested fine. Besides tearing open the tranny what other things might I look at first? I just don't know if I am seeing multiple failures or if there is a common link. So far I have seen reference to the VSS which seems to interact with all 3 of my problem items.

I'm just doing a little exploring in case there is something I missed. Oh and also what did you mean by the ECT (? what is ECT) would shut off if the heat goes up or reads too hot. My engine has been running hot due to the O/D not working. I spoke with someone on here that had some spare tranny parts a 2-3 shift solenoid and vac modulator for $40 total, maybe I should get these just in case.

 

[MrShorty]

ECT=engine coolant temperature sensor -- tells the computer how hot the engine is. If the ECT indicates the engine is too hot (don't remember what the cutoff is), the computer will disengage the TCC.

 

[AlaskanJack]

Very interesting anyone know what the temp for shut off is?


Also any comments on my post I'm interested to hear opinions.

 

[MrShorty]

Alaskan Jack: Read over your situation again and, if it were me, I'd start by checking the TCC and OD circuits carefully. They share a common voltage supply wire. Make sure you have battery voltage to that wire at the transmission plug (Get a wiring diagram so you know which color it is: It's usually red). If you don't have battery voltage there, then neither will work. Then make sure the wiring connections are good between the solenoids and the PCM.
After checking the ECT output chart, I think the PCM disengaged the TCC at about 240 or 250 F. The ECT's output voltage goes to 0 at about 260 F.

 

[explorerjoe]

If your torque converter is not locking up, be careful. I don't know if you can monitor your trans temp but mine hit 230 before I would pull over to cool trying to make it to Gallup (counting on my mobil 1 trans fluid to hold up, still smells and looks like a peach). granted, I live in a desert but it was 4:30 am. I stoped 3 times making that last 20 mile long 35mph crawl to Gallup. I even have the Factory installed trans-cooler. I will be installing a second cooler because here in AZ on a cool 110 day, my trans runs at about 190 at 70mph (all temps are pre-cooler). During all this I never had the coolant temp sensor read abnormal. Here are some interesting (not all) things that can prevent lock up:
1: Wire issues -shorts, breaks etc.
2: Malfunctioning ECT sensor
3: Malfn. Throttle Positon sensor
4: Malfn. manifold absolute pressure sensor
5: Brake switch malfn.
6: Converter clutch solenoid "dirty"
7: Clutch in converter malfn.
8: Valve body

Alaska, for curiosity sakes, what is your approximate elevation? I noticed my torque converter would not lock up even momentarily at the apex of the mountians or under slight throttle down hill - this was my first clue (it does unlock at closed throttle due to TPS data). I may have another place pull codes and then check the engine senors. I also have a hypertech chip, maybe I'll try pulling it too. Anyone have any idea the voltage the lock up solenoid should have under application?

Thanks
Joe

 

[AlaskanJack]

Hmmm very interesting...... i just removed my RABS valve since there was no exciter ring in the diff and it had been disconnected on top of the diff. Previous owner said the O/D was working even with it off.

I may need to pull my abs module under the dash. I get all the brake warning lights on the dash. I thought it was just due to the disconnected abs system. I may need to pull out my EVTM and do some checking of power to certain systems.


Oh and I am at sea level

 

[MrShorty]

The TCC solenoid circuit carries battery voltage. The computer acts as a ground side switch. Switch open TCC off. Switch closed TCC on.