VSS drops out at 77 mph (repeatably)

[9secz]

Firmware is 1.3.1
Sensor is hall effect shared between speedo and MS3x.
Rate is 8380 ppm.
Input is MS3x pin 29 (aka N2O in).
Logged speed appears to be correct up to about 77 mph.
Above that speed, logged mph is erratic and way too low.
Logged speed comes back online when vehicle speed drops below about 77 mph
Speedo shows correct speed above 77 (and everywhere else).

Question: Do I need to use another input pin to keep with with the sensor pulse rate above 77 mph?

Log file excerpt and current msq attached.

Jeff

[jsmcortina]

Question: Do I need to use another input pin to keep with with the sensor pulse rate above 77 mph?

Quite likely yes.
The "switch input" pins are designed for low frequency only. Picking up off wheel studs or similar for a low-frequency speed input should be fine. Using an OEM style speed input will likely present too fast a signal.
PT4 is a 0-5V input which can accept high frequencies. (Open-collector hall sensors would require a pullup resistor to TPSVREF 5V.)

James
EDIT: I updated the manual page with that information too.

[9secz]

I've switched my VSS1 input wire to MS3X pin 31 (from pin 29) and switched my VSS1 input pin to PT4 in Tunerstudio, and now I get no VSS indication on my TS dash or logs.

I'm sharing the hall effect speed sensor output between my speedometer gauge and MS3. My TS dash gauge and log files had seemingly accurate VSS data when I was using the Nitrous 1 input. Nothing changed but the wire move and input pin selection. Is there some jumper I need to change?

Latest msq attached.

Jeff

[jsmcortina]

Nothing changed but the wire move and input pin selection.

Did you notice my note about pullups?

James

[9secz]

I did, but I thought it only applied to open collector sensors. Did you notice my note about sharing the signal with the speedo and that the speedo is reading correctly? Last time I scoped the signal it was the expected square wave. I'll scope it again this morning to see if my new PT4 connection has degraded the signal.

Jeff

[9secz]

OK, I screwed up! I thought the scope showed my speed sensor output to be a 5 V square wave, but it's 12 V. I s'pose I've blown the CPU input, so I've ordered another MS3 board. That'll teach me to not remeasure signals before connecting to fragile inputs!

Jeff

[9secz]

Still no joy. I bought another MS3 board based on the assumption that feeding PT4 with a 12 V square wave probably nuked the CPU input. I built a 12 V to 5 V converter with an LM339 comparator and used the scope to prove that it was outputting a 5 V square wave.

But still no speed showing on my TS gauge (a gauge that worked when I was connected to nitrous in).

Has anybody accomplished this, or is VSS on PT4 theoretical at this point?

Jeff

[jsmcortina]

I'm using PT4 as my VSS input and it is working fine.

James

[9secz]

What a nasty weekend! I don't know if "Murphy's Law" is a common expression in the UK, but it sure applies to my recent troubleshooting. I finally traced the last puzzlement to the orange wire carrying the raw VSS sensor signal from the interior to the engine compartment. The wire to contact connection broke inside the connector body (a Deutsch).

Now the VSS signal is making the entire journey from sensor to my logic level converter. And the converter is getting 12 V from DB15 pin 9 (that was another thread). The converter is spitting out a 5 V copy of the 12 V sensor signal. My new MS3 board is finally working correctly (it took more than one burn cycle without changing anything to get it to wake up, but that's a thread I didn't have to post).

And my logged VSS on PT4 can exceed 77 mph!

Who would have thought that logging vehicle speed could cause so much grief!

Jeff