VSS reading as Input shaft speed?

[sporqster]

This is probably a dumb question, but can someone please point out what I'm doing wrong here? I cannot get my vehicle speed gauge in tuner studio to read anything, with the wheels clearly spinning. Scoping the VSS pin in the GPIO, I'm seeing a 5V square wave with varying frequency consistent with the speed of the spinning wheels. I am seeing readings in Tuner Studio for 'input shaft speed'... so it would seem that I somehow have the VSS mapped to the wrong channel in Tuner Studio?

Also, what's the point of an input shaft speed? My transmission (Ford AX4N from a Continental) has a VSS, but no input shaft speed sensor I know of. Assuming that no gears are broken, since the MSgpio knows the gear you're in and the VSS, shouldn't ISS be a calculated value?

Thanks!

[Bernard Fife]

sporqster,

You might have the VSS wired to the ISS input. But you might have other issues with the hardware or settings too. Some of those will be covered here: http://www.msgpio.com/manuals/mshift/vss.html

ISS can be used to calculate the converter slippage and the slippage in the friction elements as well. However, if it is not measured, it is calculated by the code (assuming no slippage in the gears) and used to estimate the converter slippage. There is more on that here: http://www.msgpio.com/manuals/mshift/V22tune.html#gn

Lance.

[blaylock]

Thanks for the reply.
I'm working on this for Sporqster,
I believe this is a code or settings issue.
We are using Tuner Studio Megashift version 2.03

Relevent test performed:
I've bypassed the input circuitry (Removed Jumpers) and have applied a 3.3V square wave Tach Signal from my Jim Stim directly to pins PT0 (VSS) and PT5 (ISS) of the GPIO board.

Result under Tuner Studio
Case1:
With the ISS alternate input disabled, my signal applied to PT0 is displayed on the Input Shaft Speed Gauge.
All VSS gauges display zero.
Signal applied to PT5 has no effect.

Case2:
With the ISS alternate input enabled, my signal applied to PT5 is displayed on the Input Shaft Speed Gauge.
All VSS gauges display zero.
Signal applied to PT0 has no effect.

Any comments or suggestions would be greatly appreciated.
Thanks again.

[Bernard Fife]

What code version are you using? What board version? What frequency input signal are you using? With the default settings, about 1600 Hz should be about 60 MPH. Have you tried adjusting the VSS filtering settings? You can read about them in the link I posted previously.

You should post your MSQ and a datalog too, it will help us see what is going on.

Lance.

[blaylock]

I found an Ini file version mismatch that fixed my VSS ISS pin mapping errors, but I still have no joy when installed on the car.

On my bench a 3.3V square wave from my Jim Stim drives a matching 5V square wave into PT0, and is now reported as speed. : )
On the car the shaft output sensor is also megashift conditioned and I scoped a 5V pulse on PT0, but only with a 10% high time.
With the wheels in the air, two separate tests (scope shots) show clean 5V signals of .1ms every 1.2ms, and .3ms every 3.6ms. Neither returned a VSS reading.

(With the same rising edge frequency as the bench test) No speed is reported : (

Is there a filter that I should turn off?
Any ideas where I should look.
Thanks,
+Paul

[Bernard Fife]

Paul,

Did you see this: http://www.msgpio.com/manuals/mshift/V22tune.html#gv

There is also more VSS info here: http://www.msgpio.com/manuals/mshift/vss.html

Lance.

[blaylock]

Thank Lance,
I never found the smoking gun, but the bugs are dead just the same.
After purging everything, I downloaded new ini files, and set up a new Tuner Studio Project.
We now have Two Megasquirts, a Megashift, and our own Torque Bias computer working together!
Woot Woot!
+Paul