lugs when upshift from 2nd

[meskidog]

heres a new one from a newbie
bought rebuilt tranny 15k mi ago and it was always a little slow going into OD. got better with time
now suddnely the darn thing is lugging and chugging when it upshifts from
2nd. acts like going 2nd to OD or else maybe torque converter locking premature.
I searched forum first for anyone with similiar issues but couldnt find any.
trying to remember if I can code check this thing to get some answer, but I figured I'd post the question and let some of you more experienced chirp in

 

[wood1]

Well, without knowing what it is doing exactly it is difficult to give advice. If you tap the brake pedal it should kick the torque converter lock off, if you select D rather than OD you should be able to prevent it from shifting into OD. What I would suggest is to adjust the bands and check the fluid level. Other than that...

 

[meskidog]

never thought about tapping brake when trying to go forward, but makes sennse. It does it in D or OD so I dont know if that helps in diagnosing. I'll try the brake tap today

 

[meskidog]

tapping brake didint help, and it does it whether in D or OD. If I keep it in 2 and get on it, its ok when I move shifter to D because engine speed is up to the range tranny must be in
fluid level is fine and fluid is clean

 

[tanbuddy]

When the truck is in 3rd or od, does the tcc lock and unlock if u tap the brakes then? Im thinking there might be a short in the line and it locks up as soon as it hits 3rd gear. Tapping the brakes wont unlock the tcc then,

 

[wood1]

Just to make sure I'm not being misunderstood, once you get the engine temp up to operating temperature and you are driving at say 45 miles an hour... if (while holding your foot steady on the gas pedal) you were to tap the brake with your left foot the TCC should unlock and you will see the engine RPM flare slightly. This should happen both when you have "D" or "OD" selected. When you move the gear selector to "D" from "2" does it upshift properly? Tanbuddy could be right, the insulation on the wiring harness in the pan will degrade and allow the wire to ground out.

 

[meskidog]

yes and yes. i did try the brake tap when it had started the lugging. it will shift from 2 to whatever it goes into if done manually with shifter.. 1 and 2 are very smoothe, but if I allow it to upshift from 2 to ... it lugs like its skipping into OD or the TC is locking,
isnt there a wire on control module that I can temporarily bypass to kinda disable the TC lockout, or are you telling me a short in the case that grounds it allows it to lock??

 

[wood1]

You can disconnect the transmission electrical connection. Then it shouldn't allow the TCC to lock or allow it to shift into OD. Take it for a drive and see what happens. Should shift smoothly through the first 3 gears.

 

[meskidog]

unplugging the main round plug that feeds trans worked. It didint lug, smoothe thru all 3 gears. Now how to troubleshoot whether its an OD or lockout problem. what tells both to activate, some kind of speed sensor
I have no check engine light but should I try to pull codes anyway??

 

[wood1]

It isn't OD as it won't shift into OD when you have "D" selected unless you have some major issues. Likely your wiring harness is grounding out inside the tranny. Probe the three terminals in the transmission harness plug attached to the transmission. If you get a ground your harness is grounding out internally. Not a big deal really, you can either replace it or repair it. It's very straight forward once you pull the pan off. There are diodes in the plug but the wires inside would be an easy fix.

I would even remove the TCC solenoid and test it. You can energize it with a 9 volt while sticking the straw from a can of WD40 in the little port and see if it is working.

Review Glacier's VB rebuild thread. Extremely informative.

If your OD is indeed engaging when you have "D" selected then you should look into rebuilding your VB. Not a huge undertaking for a gear-head but some buy a rebuilt and install it instead. Central Valve Bodies is a trusted VB rebuilder and many EF member have used their services. I did my own but if I were going to replace one I would get one from them.

You should also check your bands. Easy to do as well.

 

[wood1]

unplugging the main round plug that feeds trans worked. It didint lug, smoothe thru all 3 gears. Now how to troubleshoot whether its an OD or lockout problem. what tells both to activate, some kind of speed sensor
I have no check engine light but should I try to pull codes anyway??

There are a few items that have input to the TCC lock and OD shift. This transmission is mainly a hydraulic operated tranny but the TCC and the OD shift have electronic, computer controlled input as well.

The transmission receives input from several inputs:
1- the engine coolant temperature sensor
2- the brake switch
3- an ignition signal (rpm)
4- throttle position sensor
5- vehicle speed sensor

If the engine coolant temperature switch fails, you would never get TCC lock. The computer does not allow the TCC to lock until the engine is warmed up.

If the brake switch is stuck on (like your foot on the brake) the TCC will not lock. When you touch the brake the TCC is switched off, it will also unlock the TCC so high engine load demands are on an unlocked convertor.

If the computer isn't receiving a PIP (RPM) signal it will not allow the 3-4 shift or the TCC lock.

The throttle position sensor will cause strange shift scheduling, TCC cycling (off then on) or no TCC engagement.

Failure of the VSS (vehicle speed sensor) will prevent TCC lock, and the 3-4 shift. You would also notice that the cruise control will not work.

The truck has to be going at least 30 MPH for the governor pressure to upshift the TCC valve, then when the computer decides all the stars and planets are aligned and wants the TCC to engage it sends a ground signal to the TCC solenoid and it engages the TCC.

If you tap the brake, close the throttle, let the RMP drop low, or the coolant temp is below 128 deg. the computer will not allow the trans to shift the TCC valve. If it locks the TCC when the engine is cold or you tap the brake it doesn't unlock, that tells me that solenoid is getting a ground signal somewhere else.

I am guessing that once you are going a good clip on the highway with "D" selected with the harness connected, that if you pop the shifter into "OD" it shifts normally into OD.

Clear as mud?

 

[meskidog]

most everything you described as poss faults would prevent OD or TC lock. Tachometer works, Temp gauge works, Brake lights work, so I'll assume those items dont need immediate attention. If the computer sends a ground signal to transmission, a wiring grounding out would make the most sense so I'll start there.
I really appreciate your help

 

[wood1]

Well, the temperature sending unit for the gauge and the sensor for the computer are two different items... but I agree, I would check the wiring inside the tranny.

 

[meskidog]

tested plug coming out of tranny for grounding and neither tested ground continuity. could something in the computer be whack. since I cant tell whether its going into OD or TCC ( or both) prematurely if its not a ground inside tranny the computer is telling it to do this. Every item that controls when to shift OD or lock TCC would prevent if they failed.

 

[wood1]

Did you try driving it up to highway speed in "D" and manually shift into "OD"? If it doesn't do anything you are in OD.

Maybe a solenoid has failed in the actuated (on) position?

They are easy to test if you have them out. 9V battery.

 

[meskidog]

havent tried a highway shif because it lugs so bad didnt want to do damage. I guess i need to find a manual that has some views to tell me what solenoids are what. am i understanding that the OD soleniod being stuck open wouldnt shift into OD until tranny normally shifts into 3 because thats when it happening

 

[wood1]

PM me your email address and I will send it to you.

It lugs too badly to pick up speed? Sounds weird. I would bite the bullet and rebuild my VB, tighten the bands too (very easy to do). Once you have the VB out you can easily check the solenoids.

 

[tanbuddy]

I think its pin 54 on the computer that activates the tcc lock. Cut it and see what happens. If it runs normally its probablly a computer problem. Eather get a new computer or just add a swich for lockup.

 

[wood1]

Yes that isn't a bad idea. It did run fine unplugged.

I really don't think that the TCC locking will make the engine lug that badly. It only drops the RPM slightly. I would cut the OD solenoid wire.

Email sent.

 

[tanbuddy]

Does the a4ld allow overdrive with the torque converter unlocked? If it ran in that mode, it would acclerate very slowly, but the rpms should be around 2000-2500 or whatever the stall speed of the converter is. If it only runs locked then it would drop the rpm a lot