Gen3/4L60e swap - poor shifting in 4WD Low Range

[ergeorge]

Hi Folks,
I have a Gen3 5.3L FlexFuel & 4L60e from an 07 Silverado Classic 1500 4WD swapped into a 1993 Land Cruiser.

The swap is running great in high range. But when I put the transfer case in low range, the shifting isn't right. It seems to immediately shift to 3rd or 4th gear regardless of speed, throttle, load etc. I can get by with this on moderate terrain/load by manually shifting. But even with this it won't stay in 1st gear even with the shifter all the way down - though if I stomp on it, it will downshift to 1st briefly. But that's not a great solution on a steep shelf road with a big cliff next to you!

A little more about the swap...
The original Silverado configuration had the VSS on the transfer case output shaft. The Silverado transfer case had a 2.72:1 ratio.

The swap uses the Toyota transfer case, and to make the adapter work, I swapped the original 4WD transmission output shaft for the 2WD shaft (with tone ring) & housing. So the VSS is now on the transmission output shaft. The Toyota transfer case has a 2.49:1 ratio, which I changed in the tune.

There is a pin 16 on the PCM C2 (Green) connector labeled "4WD Low Signal" which I understand needs to be connected to ground when in 4low. However, when I do this the engine runs like crap - very rough, nearly stalling when pulling out, etc. It soon it sets code P2771 "4WD Low Switch Circuit", at which point I think it ignores pin 16 because the engine goes back to running normally and the shifting remains unchanged.

My guess is that somewhere in there, it's trying to multiply the VSS signal by the transfer case gear ratio to get the transmission output shaft speed - and getting a nonsensical result because the VSS signal is already the transmission output shaft speed. So it throws up its digital hands and posts P2771.

So, in summary...

Is there anything I can do in HPTuners to handle the change in the VSS position from transfer case output to transmission output? I suspect this is the root of the problem.

Other questions...

I haven't found anything to log that would indicate that the PCM thinks it's in 4LO vs high range? I'd like to confirm that pin 16 is doing what I think it should.

I've tried logging the transmission gear, but I don't get anything. Is this because the swap doesn't use the original external sensor mechanism & harness that sits on the shift lever shaft on the 4L60?

This post from 2015 indicates that HPTuners support can give you access to the 4LO shift tables, so I'll ask. Will that help?

Is "Performance" mode the same as "Tow/Haul" mode? Again, that other thread talks about setting up performance mode to get the shifting correct. I was hoping to have Tow/Haul mode AND proper 4low shifting, but if that's what it takes I'll do that.

Thanks!
LandCruiser_ERG_20210912_v1.hpt

[ergeorge]

bump ... any ideas?

[PRS]

Have you updated your HPT to the most recent version? In my Gen3 4L80 241 swapped rig I see the 4low tables in the software. I basically let it shift from 1 to 2 and that's it. Blocked out 3 and 4th gears cuz I shouldn't be going that fast imo.

I can't see your tune because I'm on mobile but check out your trans shift tables for the 4low section.

Edit: And yes, "Performance" mode is the Tow/Haul mode for us truck and offroad folks.

[ergeorge]

Have you updated your HPT to the most recent version? In my Gen3 4L80 241 swapped rig I see the 4low tables in the software. I basically let it shift from 1 to 2 and that's it. Blocked out 3 and 4th gears cuz I shouldn't be going that fast imo.

I can't see your tune because I'm on mobile but check out your trans shift tables for the 4low section.

Edit: And yes, "Performance" mode is the Tow/Haul mode for us truck and offroad folks.

Yea, just updated last week - running 4.12.4

I see a <Hot> and <Cruise> modes under Trans -> Shift Scheduling that I don't recall seeing before. But no 4Low

[ergeorge]

Have you updated your HPT to the most recent version? In my Gen3 4L80 241 swapped rig I see the 4low tables in the software. I basically let it shift from 1 to 2 and that's it. Blocked out 3 and 4th gears cuz I shouldn't be going that fast imo.

I can't see your tune because I'm on mobile but check out your trans shift tables for the 4low section.

Edit: And yes, "Performance" mode is the Tow/Haul mode for us truck and offroad folks.

Just took a look at the downloads page again - they don't list versions, but my install indicates that there aren't any updates available. And a quick grep of the install finds the 4.12.4 version string in the current stable download.

But I did see that they offer downloads of a Beta version - is that what you're running?

If not, I'm *really* curious how you got the 4Low tables to show up! Have you looked at the scanner to see if there's a low range status you can log, similar to the perf mode status?

[blindsquirrel]

Different *operating systems* can have different tables defined, it can be different for different OS IDs even on the same vehicle - new stuff only appears in the next VCM release if it's been added for that exact OS. HPT has to add every parameter that you see in the editor, so all the stuff you see in there is either stuff they thought/knew would be useful, or somebody asked specifically to be added. You can open a support ticket and ask if they can add the tables.

[ergeorge]

Different *operating systems* can have different tables defined, it can be different for different OS IDs even on the same vehicle - new stuff only appears in the next VCM release if it's been added for that exact OS. HPT has to add every parameter that you see in the editor, so all the stuff you see in there is either stuff they thought/knew would be useful, or somebody asked specifically to be added. You can open a support ticket and ask if they can add the tables.

Interesting - thanks.
I have an email conversation started with HPT support. They asked for some data but I haven't had a chance to do it yet.

[PRS]

4wdlow.JPG

This is what you're after.