DFCO not working, E38 shows now VSS (LS3/E38)

[eboch]

Hi All;

Struggling with this. This LS3 is a swap into a C2 Corvette. Tranny is a Tremec TKO 600. I'm taking VSS off the trans from the pass side VSS sender (12 pulses per rev). I dont need this signal for anything else.

The E38 has no TCM. The LS3/E38 are out of an 08 corvette ... auto trans. I've read that the auto trans E38 ECM cant be used in a manual car ... needs a new/different OS. Is that the case?

I have minor backfiring/burbling on decel or when I lift off the throttle pedal. Id like to get rid of that .... which is apparently related to DCFO.

HPtuners shows my DCFO as inactive ... and it also says my VSS is 0 all the time. I've checked the VSS sender (produces variable voltage when viewed on an A/C-meter ...seems to be functioning), wiring is good the ECM pins 71 & 72.

I've converted the tune to manual trans and the car runs, idles and starts fine. The ECM is configured to ignore the clutch lockout.

I've tried all kinds of combos of settings on the speedo page .... nothing seems to enable DFCO, or enable a VSS to be available on HPtuners.

Any thoughts of things to try?

Thanks
eboch

[eboch]

Here is my tune

[blindsquirrel]

The auto trans ECM is expecting to get the VSS coming in over the CANBUS from a TCM. Auto trans ECM cannot read the pins a manual trans ECM uses for the VSS connection. It does not even know those pins are there, it does not use them and there's nothing you can change to tell it to look there instead of the CAN data stream. Well, you can - by flashing it with a manual trans OS.

It's a swap with none of the other factory modules to worry about, just put the right OS in it. Must be done with GM SPS, not a HPT write-entire.

[foxls2]

The TKO for GM is a 17 tooth wheel Ford and the Magnum use 12 tooth so I'd change your PPM to 17.0000 in your tune.

[blindsquirrel]

An auto trans OS is incapable of reading any VSS of any tooth count/PPM wired to the manual trans VSS pins.

[eboch]

Thanks everyone ...

Sounds like I need to reflash with the right OS. I started another thread to discuss how to go about doing this.

Cheers
eboch

[eboch]

Update;

Got a "new" E38 out of the same year LS3 Corvette ... but this VIN was for a car that came with a manual trans (confirmed VIN with GM). The new E38 has the exact GM PN as my original E38 and also uses the same OS. I loaded the new E38 with the tune from my original E38 (which was out of an auto-trans car). Put the new E38 into the car and ...surprise ... the new E38 now reads VSS. The VSS isnt reading right yet ... I have some config issues to address .... but the DFCO now seems to be working. when I lift off the throttle between gears, I don't have any backfiring. I still have a very slight burbling if I engine-brake ... but nothing like I had before.

So ... there is something different between the two E38 ECUs ... both are from the same year LS3 Corvettes ... one auto-trans and the other manual-trans. The auto-trans E38 ECU would not register a VSS when fed on pins 71&72 by the Tremec VSS sender ... and the manual-Trans E38 ECU does.

Now I need to figure why my VSS readings are ~ 5X higher than they should be. Next challenge.

[77c10]

Did you ever get this all worked out. I'm having the same issue as you were having originally but with a t-56 Mag. I change my ECM to a manual one but I'm still getting 0 VSS so I was wondering what settings you ended on that worked for you.