Adding VSS

[curly]

I've got a G4x MX5 unit, and I'm wondering what the best method is for adding a VSS sensor. I have access and experience using BMW sensors, and OE ABS tone rings on my axles, but reading this thread makes it sound like it's a lot of trial and error, plus I don't think my unit has 8v available, and I may need it?

Other option is the OE cruise control output, which uses a magnetic reed switch once a cable rotation, however that reading is erratic, no matter the filter setting. I've praised the benefits of Link over MS to anyone and everyone that will listen, however I will say that megasquirt seems to work with this reed switch without issue. Not sure if that's a hardware of software benefit.

 

Long post short, is it worth doing the trial and error for the BMW sensor? Is there a way to make the factory VSS fuction? Is there a 3rd (GPS/VSS) sensor I should be considering?

[Vaughan]

I fitted NB2 hubs with abs sensors to mine (among other things) and hooked the factory abs sensors directly to the ECU. If you didn't mind your factory cable speedometer not working you could fit an NB2 speed sensor to the gearbox.

You can use a math block for further filtering on the read switch signal if so desired.

[Adamw]

The reed switch should work fine if it is working as it should be.  If the signal from the reed switch is not usable, then there is likely either something wrong with it or possibly the cable that is driving it.   I have fixed a GTR that had an erratic speed signal from the reed switch in the past by just replacing the reed switch, I assume they just wear with age, when you consider the common speed signal of "4000 pulses per mile", that little reed switch bends backwards and forwards a lot in 30years...

The post you linked about the BWM sensors is specific to modern "Active" or magnetoresistive sensors which are designed to be interfaced with a dedicated conditioning chipset, they output a current signal rather than voltage so that is why they are difficult to make work with conventional after-market ecu voltage based inputs.   Common hall or VR sensors speed sensors from older cars can just be connected directly and will work with nothing special required.

[koracing]

Depending on the cable type and connection types - an in-line hall sensor might work out well, also.

19 hours ago, Vaughan said:

I fitted NB2 hubs with abs sensors to mine (among other things) and hooked the factory abs sensors directly to the ECU. If you didn't mind your factory cable speedometer not working you could fit an NB2 speed sensor to the gearbox.

You can use a math block for further filtering on the read switch signal if so desired.

If possible, can you show an example of using a math block to do something like a standard deviation to remove outliers/spikes from the reported speed?

[curly]

On 10/8/2023 at 3:37 PM, Adamw said:

The reed switch should work fine if it is working as it should be.  If the signal from the reed switch is not usable, then there is likely either something wrong with it or possibly the cable that is driving it.   I have fixed a GTR that had an erratic speed signal from the reed switch in the past by just replacing the reed switch, I assume they just wear with age, when you consider the common speed signal of "4000 pulses per mile", that little reed switch bends backwards and forwards a lot in 30years...

The post you linked about the BWM sensors is specific to modern "Active" or magnetoresistive sensors which are designed to be interfaced with a dedicated conditioning chipset, they output a current signal rather than voltage so that is why they are difficult to make work with conventional after-market ecu voltage based inputs.   Common hall or VR sensors speed sensors from older cars can just be connected directly and will work with nothing special required.

That's very true. At my mileage, that reed switch has switched on and off over 560 million times. Which is why I had 30 of them delivered for $9. I figure they're the easiest thing to try, since NB ABS sensors like @Vaughan suggested would require removing, drilling, and tapping the knuckle on top of wiring it. Also, I did consider the NB VSS at the trans, however I still appreciate the (working) street dash I've got now. The Link CAN gauge I've got is about as much as I wanted to add, I'll leave the Aim screens for my work projects. I'll give the reed switch replacement a go and report back. Thanks all!

[curly]

Just a follow up, I tentatively fixed this.

I tore the speedo out of a 227,XXX cluster for testing. I was very hesitant to replace the reed switch with my amazon replacements, since bench testing with a magnet showed the reed switch working perfectly in both mine and the test unit. Spinning each with a drill resulted in an issue I've been having where there'd be random spikes to 1000-3000mph. From what I can tell, this spike was due to the original switch bouncing occasionally after it switched, causing the Link to calculate the ludicrous speeds. I cut the original out, soldered a new one on, and at least on the bench, it seems to be working properly now. 

Pic attached: you can see the little circuit board with two tabs that you can remove with two screws on the side and cut out and replace the reed switch. The OE one is soldered to the top, but the leads wrap around so it sits on the bottom of the board. All I had with me was a little propane torch, so after cutting the OE one out, all I could do was melt the solder pads and stick the new switch in. It sits about 1/8" further away from the mag disc, this may have something to do with the better signal too. Who cares if it works!