E38 VSS and speedometer issue on swap vehicle, stalls on decel

[Jpat83]

Hi all-

I have an LS7 swapped into an FD rx7 using a t56 from an 04 GTO. My ecm is from a 2013 Corvette Z06. I am currently struggling with the vss settings to get accurate speed reading in the ECM. My issue does not involve the vehicle speedometer because i am using an aftermarket speedhut speedometer that is tied into the raw VSS HIGH signal (teed off the wire near the ECM) from the sensor and calibrated properly for that. So my changes in the tune are just to give the ecm an accurate speed reading.

The existing tune had 41 VSS pulses per rev and a final drive ratio of 1.00. My understanding is this is because the corvette VSS is actually on the diff and uses the 41 teeth of the gears as the reluctor.

I changed my tire circumference and VSS tire revs per mile to match my tire size, then changed VSS pulses per Rev to match the 17 that my gto t56 has. I also changed the final drive ratio to 3.90 which is what my RX7 rear diff is. The speed was still reading much higher than i actually was traveling.

I searched and read about people leaving the VSS pulses per rev and compensating for the reluctor difference with the final drive ratio. I did 17/41 x 3.90 for a adjusted final drive of 1.62. So i tried 41 VSS pulses per Rev and ratio of 1.62 and it didn't seem to make any difference. I did not change "Driven Pulse/Rev" or "non-driven Pulse/Rev" as i could not find what this does in all my searching.

Any other ideas? I am chasing a stalling issue on deceleration and want to eliminate the incorrect speed as a factor in the stalling. The engine is stock with the exception of long tube header so I did not expect to have any driveability issues running it on the stock tune. I disabled DFCO to see if that helped and it did not.

[Jpat83]

Just to update for anyone searching, i put 66 in the vss pulses per rev and 1.00 in the final drive and it appears to be pretty accurate. I got it by taking the 17 pulses per trans output multiplied by the 3.90 to give me 66 pulses per axle rev

[Alvin]

Just to update for anyone searching, i put 66 in the vss pulses per rev and 1.00 in the final drive and it appears to be pretty accurate. I got it by taking the 17 pulses per trans output multiplied by the 3.90 to give me 66 pulses per axle rev

That's good. You could also look at a traditional E38 speedo setup.. like a camaro or something. The Vette's had a speed sensor on the rear end instead of the transmission output..

But otherwise.. no if you got a speedo working that that should be good enough. It doesn't need to be accurate for stalling issues etc.

I've left some hotrods that don't need a accurate ECU speedo reading off and never had a issue. It's when you don't have a signal at all that you can have a issue. Obviously need a accurate speedo with auto.

[Jpat83]

That's good. You could also look at a traditional E38 speedo setup.. like a camaro or something. The Vette's had a speed sensor on the rear end instead of the transmission output..

But otherwise.. no if you got a speedo working that that should be good enough. It doesn't need to be accurate for stalling issues etc.

I've left some hotrods that don't need a accurate ECU speedo reading off and never had a issue. It's when you don't have a signal at all that you can have a issue. Obviously need a accurate speedo with auto.

I actually tried looking at a camaro tune. I tried a couple different combinations but it seemed like the final drive ratio never changed the speed reading, that's what made me try leaving it at 1 and doing the math. I know it doesnt need to be dead accurate, but i was wondering if DFCO was part of my issue and that has enable and disable speeds.

It wasnt my issue but i at least eliminated it as a contributing factor

[Alvin]

I don't like using DFCO or CFCO with any reasonable sized cam and I'd likely have it off just for being in a hot rod anyway. DFCO can very much cause stalling or return to idle issues. I've never had it help driveablity.

[Jpat83]

I don't like using DFCO or CFCO with any reasonable sized cam and I'd likely have it off just for being in a hot rod anyway. DFCO can very much cause stalling or return to idle issues. I've never had it help driveablity.

My ls7 is 100% stock. I tried turning DFCO off and CFCO off and it made no difference. Im trying to get everything functioning as it should in the vette