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Discussion Starter #1
Alright, i finally started up the truck yesterday. After checking for leaks, i wanted to mover her around in the driveway. Once i got it in the road though, I had to take it for a spin. The truck is still naked and i dont have tags, insurance so i only took it down the block. I was expecting to not even shift out of first because i have not gotten the controller for the 4L80E yet. in the half mile i went, i was able to get through third and up to 40mph. I didnt have enough room to get it fast enought to see if the TC would lockup but i was suprised to say the least. I do have a good tach signal that is registering in the cab but no TPS. The trans shifts really clean and with my foot in it, it shifted at 2200 rpm. Is this suppose to happen? What is the purpose of the controller? Would it hurt the transmission to keep running it like this. I am not a transmission expert so any help is appreciated.
thanks
 

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Do you still have it (the transmission) connected to the factory engine ECU? The engine ECU may just be confused and telling the tranny to shift..... In which case, you may be able to save a pile of money... This is very interesting.. Because I've had several tranny shops tell me the 4L80e can only shift into 2nd gear hydrauliclly.... Everything else takes and electronic signal.....
 

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Discussion Starter #5
once i get the truck road worthy, i will be able to tell for sure if it shifting into third and locking up but here is what i am thinking. The ECU is connected and i co have an accurate tach signal going to the ECU. To my knowledge, the only other signal that the computer needs is a throttle position. I would think that the only reason a throttle position is needed is to for kickdown purposes. 96 was the first year that the 6.5's switch over to electronic injection pumps and a "fly by wire" throttle set up. this fly by wire setup is what i am thinking tells the computer what position the "throttle" is in. Right now, i have removed this special gas petal and put a conventional gas petal in so i could attach the throttle linkage. I am thinking that by using the old gas petal and connecting the fly by wire system back up, and then adding a bracket to the gas petal for my throttle cable needs, that i can trick the computer into thinking everything is alright. This is all based off the only 2 inputs needed is RPM and TPS which i think i can provide through the factory harness. Thoughts?
 

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Shifting

Don't wait for us to tell you what to do!
Try it and you tell us!
You can always change it back.
At least you'll know.

EZ
 

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In reality you need a VSS signal, TPS, Coolant Sensor, and input speed sensor. If you pull codes you will probably see that there are some error codes, and most likely the trans has gone to full line pressure as well to compensate. I wouldn't recommend driving it like this for long, you can do pump damage by running high pressures.
 

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You have everything hooked up minus a TPS by the sound of it. I don't know why you're confused that it's working, it just isn't going to work correctly. Without a TPS the tranny should be at minimal line pressure and using part throttle shift points.
 

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Discussion Starter #10 (Edited)
In reality you need a VSS signal, TPS, Coolant Sensor, and input speed sensor. If you pull codes you will probably see that there are some error codes, and most likely the trans has gone to full line pressure as well to compensate. I wouldn't recommend driving it like this for long, you can do pump damage by running high pressures.
the VSS is pulled from the tailshaft of the transmission?? the TPS i have talked about. What coolent sensor are you talking about? Is the input speed sensor taken off of the Torque convertor, if so i havent messed with that either. I am not very knowledgable on transmissions, why would a trans go into full line pressure mode?

F250, I think i am so suprised because i keep reading about all these people that have to buy controllers (even when the trans came factory in the truck) and i was expecting to have to do the same. Does minimal line pressure hurt the transmission? untill i get the TPS deal sorted out, from what i understand the truck will not down shift and will go through the gears fast right?

Hopefully this weekend i will focus on getting the truck ready for the road and not be working 14 hour days. As always, thanks guys
 

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Thinking about the parts when I rebuild my tranny...

Yes if low line pressure your clutch packs will slip causing accelerated wear. Eventually there will be no fiction material left on the clutch disks and that material will be in the fluid clogging your filter potentially reducing flow, eventually metal shavings from further wear (if you could get the tranny to move the vehicle anymore) will flow through the tranny and cause other damage to bushings and seals.

High line pressure can blow seals and then you'll get low line pressure because the seals can't hold pressure anymore and you'll get back to slipping. Or depending on what seals, will screw up shifting. Seems to me that high line pressure would suck more power from the motor to generate.

The nice thing about an aftermarket controller is that you'll be able to program the tranny to work with the way the cummins engine builds power. The diesel will need more line pressure at a lower rpm to be able to hold the torque. There's more to it than just what rpm to shift; line pressure, how much and when is also important (something I didn't know at first).

Side note:
I echo turbos10 about the stock GM diesel torque converter not being a perfect match for the 4bt or 6bt. It works fine, accelerates the truck reasonable well, but feels a little loose. I drove a big block suburban (still a gasser but lots of torque down low) that was hooked up to a 4L80e to see how/when it shifted and it felt tighter than mine (of course I'm running 38s and 4.11 so that probably has something to due with it), but not by much. Because I'm picky perhaps a custom made Tconverter should be in my future budget.
 

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Do the aftermarket diesel guys sell a converter for these that is low enough stall (realising that it is likely variable stall, so just biasing the variable range lower)?

I know places like Huges make all sorts of 'high strength' converters for these (triple disc lockup clutch, Billet cover, furnace braze, tig, blah, blah, blah). All the stuff I see them, and others, list for diesels are for the higher rpm engines (I haven't seen one for a 4L80 behind a 6BT for example, I don't expect them to list a 4BT, or especially a 4BD:rasta:).
 

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On an electronic GM trans, most transmission codes will cause the trans to go to full line pressure as a precaution to prevent clutch slippage. Since it doesn't know exactly what is going on, it errs on the side of caution. Shift points are still made by the ECM as best as it can. The ecm is in essence working blindfolded. With no power to the EPC, it goes to full line pressure, it takes 1.0 amp to bring it to low pressure. When looking at a scanner you will see amp readings from 0.0 to 1.0 depending on TPS voltage and road speed.

The 4l80e has two speed sensors in the case, an input and output. Early systems used both, later 4wds still had the rear sensor in the case, but it was not used as it relied on the the VSS in the tcase. So, even without a TPS, the ECM is determing throttle percentages from changes in input rpm. It is not the most accurate, but the ECM is doing its best to keep working with missing sensor signals.

The temp sender I was talking about is the one in the trans pan attached to the wiring harness on later styles, early ones had a sensor actually screwed into the valve body. I erred when I said said Coolant sensor, I meant Temp Sensor.
 

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Discussion Starter #15
alright, i dont want to skrew up the transmission so let me try to work this out. I would obviously like to not buy a 1000 dollar controller if i dont have to. I know that they are super sweet and you can control shift points and what not but i am not in need of that capability at the moment. If i get a good TPS signal going to the transmission, would this fix all of my possible line pressure problems? are there any other sensors that i am leaving out? The transmission was never unhooked so whatever sensors on the transmission is still on the transmission. Id imagine the best thing to do would first be to scan for codes and see what is turning up. Thanks guys.
 

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I'd think that you'd definitely want a TPS from a diesel application so that it gets the line pressure right, or at least better for the diesel torque curve. It would be interesting to see the different torque curves between the 4bt/6bt and the 6.2/6.5 GM diesels. That could help to determine when more line pressure should be applied.

I think the internals from a diesel 4L80e is the same as a gasser (didn't see a diesel vs gas rebuild kit), just the torque converter and external electronics are different but I could be wrong.
 

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I think you're on to something. Get a TPS hooked up, then run it some and see if it codes you. If it doesn't throw codes, your golden and you've saved all of us who've got a 6.5 and want to go to a 4bt/6bt a LOT of time, effort, and money......
 
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