Swap from AWD to 4X4 two speed TC

[mikez71]

Ah yes, I searched Chevy and not GMC.
However that file of yours does not have a low speed Pattern B, so I am assuming not a 2 speed 4WD.

 

[SpareParts]

Maybe not. In the repository there is no way to tell.

 

[SpareParts]

I'll look some more. see what i can find

 

[SpareParts]

Posted looking for it on HPT Forum. See what happens.

 

[mikez71]

I doubt there will be much difference from '07 to '12 on the 4LOW map with same engine/trans combo. The normal 3.08 vs 3.42 is essentially identical but scaled. 6.2 normal maps changed a little, with later ones a little more aggressive in spots.

And really you should just test it, just in case I'm wrong about pattern B being 4low I'm a little surprised pattern B WOT shift rpm is only 3000. 4LOW schedule (if used for anything) has 4500 for the gears past 1st.

If I'm wrong, it sounds like the offroad conversion guys tune it, so they should know forsure.

 

[j91z28d1]

I kow nothing at all about auto tranny tuning. but I am curious why 4 low has special shift maps?

 

[mikez71]

Same as having different shift maps for different rear end ratios. Except the ratio difference is more extreme.

Running normal maps while in low gear, you'd be spinning the motor almost twice as fast to go the same speed. So you would really be winding it out.

If you reverse that, and run 4low shift maps with normal gearing, you would be short shifting. (at medium to high throttle positions anyway, light throttle the 4low is fairly aggressive)

 

[mikeyss]

I'm not sure if this helps any, but my 09 Tahoe came from the factory with a 6.2 and has a 2 speed transfer case. Maybe the programming it has may be different than the trucks files you've been looking at.

 

[SpareParts]

I think that is what i need.

 

[j91z28d1]

Same as having different shift maps for different rear end ratios. Except the ratio difference is more extreme.

Running normal maps while in low gear, you'd be spinning the motor almost twice as fast to go the same speed. So you would really be winding it out.

If you reverse that, and run 4low shift maps with normal gearing, you would be short shifting.

are the shift points mph based and not rpm based?

 

[SpareParts]

It shifts by speed and load.

 

[j91z28d1]

It shifts by speed and load.

I see how that could be a problem.

huh. segments swap is what you guys are considering? never done one. but seems like what you'd need.

 

[SpareParts]

No. More swapping the numbers from all the little boxes of a Pattern B 4X4 over to my Pattern A essentially turning tow/haul into 4X4 mode.

 

[mikez71]

are the shift points mph based and not rpm based?

speed and throttle position

huh. segments swap is what you guys are considering? never done one. but seems like what you'd need.

Looks like segment swap is for older PCM's. It will only swap segments with the same OS id. He would have to try a different OS. I have heard someone getting '13 OS to work in older setups, but only verified on '08, and even then it's a little process and does throw a code, though it can be turned off apparently.

I'm not sure if this helps any, but my 09 Tahoe came from the factory with a 6.2 and has a 2 speed transfer case. Maybe the programming it has may be different than the trucks files you've been looking at.

Forgot about that setup! While programming maybe different, the shift schedule should be what GM would have put in his truck, had he a 2speed xfer case.. (Truck schedules of those years are the same as SUV from what I remember. I suspect the '09 4low is likely identical to 2012 4low)

 

[SpareParts]

Mikez71.
How did you make that graph in post #31?

 

[mikez71]

You click the icon that shows two windows side by side, or in that case top and bottom.

2nd row of icons, 2nd icon. Circled in red..

 

[j91z28d1]

speed and throttle position


Looks like segment swap is for older PCM's. It will only swap segments with the same OS id. He would have to try a different OS. I have heard someone getting '13 OS to work in older setups, but only verified on '08, and even then it's a little process and does throw a code, though it can be turned off apparently.


Forgot about that setup! While programming maybe different, the shift schedule should be what GM would have put in his truck, had he a 2speed xfer case.. (Truck schedules of those years are the same as SUV from what I remember. I suspect the '09 4low is likely identical to 2012 4low)

ahh. I didn't realize segment swapping was only for older pcm's. sounds like you guys are on the right track with using tow button then.

can you do the math you want your max mph 4th gear shift point to be in 4lo. final gear ratio and tire size. go to the last column, 3-4 at 50% and plug that in there. then graph, grab the graph with the mouse at the other data points and make it looks like a smooth curve. test drive and adjust?

I'm guessing 50% column is held out to 100%? should kinda be labeled 50% and above?

for the 4-3 paste new and subtract 11mph?

 

[SpareParts]

That's cool!
Check out the difference between normal, pattern A, pattern B

 

[SpareParts]

Seems like you could use BlueCat to make a pattern A that simulates a 4lo mode then copy that over to pattern A?

 

[West 1]

I appreeciate you guys doing the hard work on this conversion. My 08 Denali has full time 4x4 and that is one issue I would like to fix if I keep it long term. So far it seems like a swap is possible but the factory computer controls or monitors are just not lining up. I hope you get this map figured out so you are more happy with the swap.

Last year my Denali really let me down while trying to pull a stump out. It started pulling hard but just before the stump pulled my front wheel started spinning so I lost all pulling power. The full time transfer case sent more power to the front axle than the rear axle where I have a limited slip and much more traction to fall back on. To me this really killed any love I had for the full time system. 4 low would have also helped a lot pulling that stump.

Your swap when successful will be a very nice addition.