Need some Microsquirt experts! 2 stroke content!

Hey everyone, this isn't four wheel related, but I'm hoping that the hive can help in some guidance before I pull the trigger on the MS system. It's been a long time since I've had my hands in one, I had MSnS in a 20v Toyota ages ago, but a lot has changed. 

Victim: 

2012 Ossa Explorer trials/trail bike

Problem:

My ECU fried itself via one of the pins, unsure why. 

Real problem:

ECUs are NLA, Ossa is out of business (for now), and production numbers were low. i.e. Replacements are nowhere to be found so far

Plus side:

The Ossa is already fuel injected, and through some folks in the community, there is a wealth of information on how the sensors behave. For sensors, it has:

Barometric pressure sensor in the airbox

TPS

5 tooth signal wheel

Coolant temp

Intake air temp

The factory system runs Alpha N, and performs admirably for what it is. The injector is in the top of the crankcase, and the reed valve is only handling airflow. Keep in mind this is not a motorcross screamer, but a low end tractor type of powerplant. 

The bike has an onboard 12v "start up" battery that will aid in keeping the ECU awake before/during startup (kickstart only), afterwhich the onboard stator can take over and recharge the system. It is how the factory ECU handles it, should be fine. 

Main questions for the group: 

1. Is the sensor suite as presented able to run Microsquirt? 

2. Does the hive suggest an O2 sensor, EGT sensor, or plug chops for tuning? 

3. If I have no base maps, is this even doable? Am I out of my mind? 

I'm curious what y'all think. At this point, the bike is a paperweight without an ECU. And due to low user base, finding a buyer for the parts (if I went that route) is difficult. So I figure, put some money to towards trying to sort it out, and if no go, then I have a MS system to use for something else in the future. 

Cheers!

The sensors mostly sound fine; I'd like to see a picture of the trigger wheel to see if it's a compatible pattern. You'll want a wideband O2 sensor for fuel tuning, but that could be a temporary dyno install. And the manual walks you through putting together a startup map.

Agreed with the trigger wheel questions Matt had, as well as trying to see what kind of sensor it uses. Usually a vr will be 2 wire or 2+1 shield with two pins measuring 500-1k ohms. Hall will not show continuity on any pins, but can usually be figured out from wiring diagrams or brute force methods. 

In reply to MadScientistMatt :

Matt, here is the page that Konrad (Ossa community member) put together on the trigger wheel, what do you think? 

https://www.ossa-efi.com/home/electrics/rotor-flywheel

My hope is to use the actual Ossa sensor to drive the MS, as space is tight, and fabricating something for that space is outside of my scope currently. 

I am curious about tuning a 2 stroke with an o2 sensor, some say it's a no go, others say that it's just going to run rich and you'll get a season out of the sensor before it fouls. 

I figure, if I can get a good base map, in most all riding conditions and temps, I can remove the o2 sensor and only use it if something changes or goes haywire. Fuel consumption is not as important to me as opposed to not fouling plugs. The Ossa does pretty good already with a very lean 100:1 oil ratio, but it's still something that I need to keep in mind. 

Unfortunately that would need a different tooth pattern.

O2 sensors will still work here, just will have a limited lifespan. It's no big deal to remove the sensor after tuning.

In reply to MadScientistMatt :

Thanks Matt, I was afraid of that. 

Do you have a better online resource for what the MS is looking for in a trigger wheel? My setup 20 years ago used the standard 36 tooth setup with EDIS, and it seems like a lot of knowledge is assumed these days. Or buried far in the manual where I can't seem to find it. 

Mainly, my question would be if I could modify that wheel to work with the system. It's very unlikely the bike will ever run with the factory system again, so if I need to make a permanent modification to that wheel, I'm happy to. 

Thanks for your help with this! 

A 36-1 pattern would be great, but the most important rules are an integer number of degrees between teeth and a gap one or two teeth long. Alternatively, you could use equally spaced teeth with a second sensor reading a single tooth trigger.

MadScientistMatt said:

O2 sensors will still work here, just will have a limited lifespan. It's no big deal to remove the sensor after tuning.

But the people on msextra will throw fits that you're not running closed loop! 

Apples and peanuts, but between cyclical misfires and a degree of fresh air getting blown out the exhaust unperturbed by being in the chamber for the combustion event, a wideband may also be useless.  It would help you get in the ballpark but in the end you may just have to tune by feel.

In reply to MadScientistMatt :

Man that is unfortunate. 

Do you know if there is a sort of collection of possible trigger wheel combinations and the needed sensors anyhwere? 

Can one of the pros check this for me and see if my gut feeling is right? 

https://www.ossa-efi.com/home/reverse-engineering

This is the waveform off of the factory rotor. Am I correct in my understanding that it could be possible to eliminate the 'long tooth" (the one making the unique signal at the beginning of the scope) and possibly use the factory signal to drive the MS? 

In reply to Steve :

I'm wondering if it might be possible to alter that signal so that the Microsquirt could run off of the negative voltage spikes, that looks like a 5-1 trigger wheel signal as-is. The biggest issue with that might be the low resolution.

This a twin or a single? If its a twin you need at least a 4-1 and an even number of main teeth. Single with a 5-1 may be possible but never tried. 

This is a single, 280cc. 

I forgot to mention, from the fella that pulled that waveform, here is what he said: 

"Note that the waveform needs to be turned upside down (the runt pulses should be low-going).   Did not realize that when I arbitrarily connected the 'scope to a running bike"

From my very limited understanding of the system, I believe it to be using the negative double spike as the ignition trigger. 

Think this may be possible? 

Yes. The trigger wheel looks non-trivial to replicate with an alternate arrangement of teeth, but 5-1 or 5+1 should work IF the 5 are evenly spaced...looks like modifying the teeth on the factory wheel is much more toward trivial machine work, so maybe selectively trimming the ends (resulting in a narrower pulse) can get you there. Getting MS/uS to electrically accept the sensor output is easy, whether by adjusting trigger settings or adjusting trigger circuitry. 

It may be possible but it may run horribly...would modifying the encoder ring on the flywheel be an option? If you could double the cutouts on the flywheel that would get you into the lower range of trigger wheel resolutions that have been tried before.

Lowest missing tooth wheel count I'm aware of having run successfully is a 4-1, so it's not an impossibly low resolution.