Ah! I've been quite interested in this for years - never made it to the top of my "list of stuff I'll actually do".

I have no ABS, and I DO have the OEM VSS, but I've been wanting to make the MS apply my correction factor directly - as tire shape changes with speed (both larger from spinning and smaller from wrinkling), correlating GPS speed with pulses seems the way to go - then apply a correction algorithm to the input (be it ABS or VSS). I already take the VSS into the MS3Pro, but using the output to drive it makes sense.

Can you be more specific about this dwell time thing (or was that only for the tach)? As both have the same issue (https://abefm.smugmug.com/Miata/Modi...Tach-Response/) it would be nice to let the ECU just do ALL the corrections.

 

We literally just connected an injector out with a 1k pullup to 5v, to the orange speedo wire. Set it up in MS3 and bam, it worked. Left the other yellow speedo wire floating

This has not been road tested, only tested up to about 45mph by spinning the front wheel.

 

I should just try it. What really killed my motivation was the lack of scaling options in MS.

 

I'll borrow a function generator from work and see what speeds I can get out of my spare cluster.

 

Oh, yeah, that would be good. I wonder if I have one? No. Spares of everything but what I need. :-)

 

I have a spare cluster. And a MDO4k. It might even have a function generator output...

 

I think when I was doing it I used the Jim Stim. Drove the MS and compared screen to physical tach gauge.

""I fed the tach known spaced tach pulses, and found that the tach is accurate at low RPM (1000), and from ~1500-~4000 is picks up linearly about 175 rpm of offset (it reads high). Then it stays there until ~7200 (reading ~7375) and by 7500 it's reading correct again, which it retains through 8000 rpm, which is as high as I tested.""

There's my super-scientific data. Enough to know something's wrong, not sure enough of it. :-) But both tach and speedo should have ~7 point tables or a simple formula to tweak the output. The MS should be able to drive all of it - and it already knows the engine/road speed, etc, so why not do it there?

 

Here are my manual tach corrections. Big pain in the *** since it's obviously non-linear. I'm using scaled piecemeal functions for the moment (imagine point to point lines). Need to check against my 2nd cluster to see if the results are valid and not some inherent manufacturing differences (and create a few additional data points). Don't worry too much about how this data is actionable, this is primarily to see if wolfram alpha could create a best fit line that looked halfway implementable (hint: it didn't).

Did I mention I have this on my bench reading data from megasquirt thru canbus right now? Too cold to work in the shop so I'm working on my bench. I need to get the LFX running to pull OBDII data, but I can compensate for transaction times and other gotchas via MS. Been playing with the timer0 prescaler to try and knock out some jitter. Needles aren't flapping but it could always look better through the scope.