LB7 with standalone 4L80

Hi everyone...

Quick question. Im making a standalone LB7 harness for a customer who is mating it to a 4L80. Unfortunately I cant use a factory T42 from a Duramax Express van because the T42 speaks 500k GMLAN, and the LB7/LLY Duramax ECM's only speak 250k J1939 CAN.

So obviously he is going to need a standalone controller for the 4L80. After a lot of research, the US Shift controller looks like a really nice affordable option that has good support/warranty, and is spoken highly of on the forums from what I can see.

What I am trying to figure out is how to wire the VSS. Obviously the US Shift will have to read output speed directly from the 4L80 Variable Reluctance sensor.

Now…what to do with the ECM speed sensor input?

The US Shift controller has an "output" that you can hook up to an electronic speedometer. You can configure the US Shift to do the equivalent of what the Allison TCM does in a factory application; TCM reads the signal directly from the AC variable reluctance sensor, then converts it to a DC square wave signal, and outputs the replicated-TOSS signal to the ECM input.

So I have two options:

Run an automatic/Allison-trans OS in the ECM, and then tie that replicated TOSS square wave DC output from the US Shift to the "replicated TOSS input" (normally comes from the allison TCM) on the Duramax ECM.

Run a manual-trans OS in the ECM…and tie the VSS output from the US Shift to the "VSS sensor input" on the Duramax ECM (like, the input where the AC variable reluctance sensor on a ZF6 ties into the ECM).

The interesting thing, is that the input pin on the ECM is the same regardless of manual or automatic. On automatic trucks, the replicated DC digital TOSS signal from the Allison goes to X pin (I forget the exact pin) on the ECM…and on manual trucks, that same pin is used for the "VSS high" input directly from the AC variable reluctance sensor on the ZF6. Then the "low" of that sensor is tied to a spare unused ground on the ECM that obviously isnt used on Allison trucks.

So it would seem that that specific pin on the Duramax ECM is capable of reading AC variable reluctance sensors directly, OR a digital replicated TOSS DC signal from the Allison TCM.

I assume its in the calibration that tells the ECM how to interpret that pin? And what kind of signal it should expect on that VSS input pin??

I think the "safer" route is to run an automatic OS in the ECM, because then I know the input from the US Shift will work properly. But as far as the ECM not seeing the Allison TCM there…even with all the DTC's disabled, doesnt it still cause some weird defueling issues?? I dont know, because all of my previous non-Allison standalone setups, I just run a manual-trans OS, and provide the customer with a plug that hooks directly into the speed sensor of their manual, or non-electronic automatic transmission…so its not a problem.

But with this setup, Im not quite sure how to set it up….

I suppose I could also run a manual trans OS in the ECM, and add a capacitor to the output from the USShift…that would effectively turn the square wave DC output of the USShift into an AC signal that a variable reluctance speed sensor would output. And then hook that up to the Dmax ECM's VSS input that would normally be hooked up to the AC variable reluctance sensor on a ZF6.

As I said above…Im leaning towards running the Allison auto OS in the ECM, disabling codes, disabling defueling, and then copy-past torque tables from a ZF6 tune.

But then the problem is cruise control. If the Duramax ECM doesnt see communication from the Allison TCM, doesnt it disable cruise control altogether??

Thoughts?

Ben

I'm lost...........but you will probably figure it out.

Good luck !!

Is it by chance going in a 4X4 truck? If so you could use the transfer case sensor for the ECM.

I had a few guys want a stand alone there was a couple tcm used in the 6.5 diesels to control the 4l80e part # 16196390 and 16128420 ive seen them used on the P30 bread vans and so forth all they take is a vss tps and map signals to work. Tunercat does have the definition file to edit the file but like the old obd1 stuff you will need a chip burner.