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OBD-II - Tripping the TFT Hight Temp in a 6.5L & 4L80E

J

JayTheCPA

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Question: What actually (mechanically) happens when the ECM commands the TCC to lock-up due to high transmission fluid temp?


Here is what I think I know based on what I have read:
> The ECM (16216588) monitor's trans fluid temp.

> When trans fluid is too cold, the ECM prevents OD engagement.

> When trans fluid is too hot, the ECM commands TCC lock-up to try and dump the fluid's heat. Or more specifically, stop generating heat from letting the TCC slip.

> IIRC, the high temp / TCC lock-up point is controllable via a table that the ECM reads.



Goal:
> Learn the mechanics of what happens when the 6.5's ECM triggers the high temp mode.



Discussion items:
> Does the 'brake apply' signal still force a TCC disengage even when the temp is high?

> Are the characteristics different from OBD-I (16183977 / 16199980 / 16212488 / 88961136) to OBD-II (16216588)?

> Aside from TCC lock-up, does the ECM command any other action while in high temp mode?

> Ignoring effects of heat on the trans fluid, are there any long term negative effects to the 4L80E by the ECM setting the high temp mode?

> Does the ECM (at least somewhat) gracefully allow shifting while in TFT high temp mode?


Author's request to Mods: Please keep this in the 6.5 section as the core components to the question are unique to the 6.5 platform; specifically, the ECM (and its data tables) do not port to other platforms (that I am aware of).
 
The transmission appears to shift w/o the TCC locked to prevent snapping the "fragile" input shaft. I can confirm that extended WOT in 3rd gear towing will lock the TCC due to temps. I confirm shifts are with the TCC unlocked in the hot mode. When I override the TC the shifts bang in. This is not as useful as assumed because the TC clutch is weak and really doesn't hold as well as it should at full power. Noted above tested on 1993 model year.

I imagine the pressures in the trans go up to help stop slipping with hot oil, but, I am guessing. I can slip the stock TCC badly at light throttle when commanded to lock at 35MPH. Yet it doesn't fry at 65 MPH in 3rd flat out. (The Yank triple disc solved the low speed slipping.)
 
Do have a vague memory recall where the line pressures go up during high temp mode. Presuming this is true, what are the long term effects of high line pressures?
 
Also keep in mind the ECM controls transmission fluid pressure via a pulse width modulated solenoid. There is no pressure sensor in the trans, so it controls the pressure by refernicing RPM's VS trans temps. As fluid heats up, it takes more from the pump to hold pressure, so if the temps it is receiving is different from what the fluid actually is, the pressures can go high or low. And a large portion of the fluid that lubricates the trans and flows through the cooler is bypassed fluid from the pump that it bleeds off to keep pressures down. So raising line pressures can actually reduce cooler flow at lower RPM's.
 
THEFERMANATOR said:
Also keep in mind the ECM controls transmission fluid pressure via a pulse width modulated solenoid. There is no pressure sensor in the trans, so it controls the pressure by refernicing RPM's VS trans temps. As fluid heats up, it takes more from the pump to hold pressure, so if the temps it is receiving is different from what the fluid actually is, the pressures can go high or low. And a large portion of the fluid that lubricates the trans and flows through the cooler is bypassed fluid from the pump that it bleeds off to keep pressures down. So raising line pressures can actually reduce cooler flow at lower RPM's.
Click to expand...
FERM, what about the manifold pressure switch/trans pan temp sensor does that just monitor that pressure is present w/o considering pressure?
 
JayTheCPA said:
Question: What actually (mechanically) happens when the ECM commands the TCC to lock-up due to high transmission fluid temp?


Here is what I think I know based on what I have read:
> The ECM (16216588) monitor's trans fluid temp.

> When trans fluid is too cold, the ECM prevents OD engagement.

> When trans fluid is too hot, the ECM commands TCC lock-up to try and dump the fluid's heat. Or more specifically, stop generating heat from letting the TCC slip.

> IIRC, the high temp / TCC lock-up point is controllable via a table that the ECM reads.



Goal:
> Learn the mechanics of what happens when the 6.5's ECM triggers the high temp mode.



Discussion items:
> Does the 'brake apply' signal still force a TCC disengage even when the temp is high?

> Are the characteristics different from OBD-I (16183977 / 16199980 / 16212488 / 88961136) to OBD-II (16216588)?

> Aside from TCC lock-up, does the ECM command any other action while in high temp mode?

> Ignoring effects of heat on the trans fluid, are there any long term negative effects to the 4L80E by the ECM setting the high temp mode?

> Does the ECM (at least somewhat) gracefully allow shifting while in TFT high temp mode?


Author's request to Mods: Please keep this in the 6.5 section as the core components to the question are unique to the 6.5 platform; specifically, the ECM (and its data tables) do not port to other platforms (that I am aware of).
Click to expand...
Low temp is around 28 deg. f for OD if my old memory bank is still working right.
 
WarWagon said:
The transmission appears to shift w/o the TCC locked to prevent snapping the "fragile" input shaft. I can confirm that extended WOT in 3rd gear towing will lock the TCC due to temps. I confirm shifts are with the TCC unlocked in the hot mode. When I override the TC the shifts bang in. This is not as useful as assumed because the TC clutch is weak and really doesn't hold as well as it should at full power. Noted above tested on 1993 model year.

I imagine the pressures in the trans go up to help stop slipping with hot oil, but, I am guessing. I can slip the stock TCC badly at light throttle when commanded to lock at 35MPH. Yet it doesn't fry at 65 MPH in 3rd flat out. (The Yank triple disc solved the low speed slipping.)
Click to expand...
It appears the 4L80e should have come from the factory w/triple disk TC but such an animal has not been available for long "a great mod."
 
FellowTraveler said:
FERM, what about the manifold pressure switch/trans pan temp sensor does that just monitor that pressure is present w/o considering pressure?
Click to expand...
The manifold switch is comprised of nothing but on off switches. It tells the ECM what position the manual shift lever is in. As the shift shaft moves through it's bore in the valve body, it directs fluid through ports that trigger the switches in the manifold switch to tell it what gear is selected, it then uses the input and output speed sensors to calculate the gear ratio. Newer trans use the manifold pressure switch to tell the TCM where fluid os being routed to know which clutch packs are being applied, but the 4L60E and 4L80E used a cruder earlier design for shifting. And the temp sensor in a 4L80E is in the internal trans harness, the 4L60E had it in the manifold pressure switch.
 
FellowTraveler said:
It appears the 4L80e should have come from the factory w/triple disk TC but such an animal has not been available for long "a great mod."
Click to expand...
Theres no need for a triple disk converter and a 4L80E in stock form. A single disk converter can be built to hold around 700-800 foot pounds of torque with the addition of a billet cover and apply piston. An ALLISON up to 2010 still only came with a single disk converter that was the same size as the 4L80E's all the way up to 2010, and in 2011 they went to a double sided friction is all.
 
FellowTraveler said:
Low temp is around 28 deg. f for OD if my old memory bank is still working right.
Click to expand...

Have not experienced that one yet :)

The OE temp I have in mind is around 70F and need a go-back to an earlier comment, the ECM will still engage OD while the TFT is cold, but observed it does not lock the TCC until above ~70F.



THEFERMANATOR said:
Also keep in mind the ECM controls transmission fluid pressure via a pulse width modulated solenoid. There is no pressure sensor in the trans, so it controls the pressure by refernicing RPM's VS trans temps. As fluid heats up, it takes more from the pump to hold pressure, so if the temps it is receiving is different from what the fluid actually is, the pressures can go high or low. And a large portion of the fluid that lubricates the trans and flows through the cooler is bypassed fluid from the pump that it bleeds off to keep pressures down. So raising line pressures can actually reduce cooler flow at lower RPM's.
Click to expand...

Excellent information! :D:D:D

It looks like the ECM actually wants to maintain a fairly constant pressure by adjusting the pump to account for calculated fluid density; correct? Related question, is the pump output fairly constant (by RPM) and the line pressure controlled by the bleed-off?


So, scenario: the fluid is actually significantly colder than what the ECM calculates.

From this information, it seems logical that the ECM will presume the fluid is less dense (due to the warmer temperature), send more fluid to the tranny, and less to the cooler; correct? Presuming this is correct:

> What is the long term effect on the pump? Is it rated for continual use this way, or will it shorten life?

> Will this create a self defeating situation where the tranny may actually get hotter due to less fluid going to the cooler?
 
That 28 deg. f was something I had picked up when researching transmissions fluids for extreme cold operation of the 4L80e and pure synthetic was deemed to be the best solution for extreme cold protection of transmission components. I suspect someone familiar w/trans controller programming would know for sure.

I had many individuals claim I was running my transmission too cold and condensation moisture would build up but the torque converters normally run a 300 deg. f or higher with high stall & torque multiplication so that dispels the water buildup claim I'm at almost 7 years w/high end rebuild transmission is like the bay it was rebuilt even the AMSOIL looks like the day installed.
 
Mine wouldn't go into OD until it got to a certain temp, and lockup was prevented until the engine and trans were above another temp. The no lockup is moreso to allow the engine to warm up, and not lug a cold engine. And no OD is also to keep RPM's up to allow the trans to warm up faster.
 
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