MicroSquirt.com read only forum (Jan.15,2018)

I started to tune and found my cranking RPM's were about 800?

Interesting. This makes me realise that there might be something fundamentally wrong about the diagram I gave you for the 'diode and resistor' circuit.

A little history is appropriate at this point:
The circuit is actually the work of Matt_gsxr who was pretty active here on the Megasquirt websites for a while, although I haven't seen him post lately. I took the diagram of his circuit (the drawing of it is his work also) and I modified it slightly for my project which is an inline 2 cylinder motorcycle engine with wasted-spark and a 180 degree crankshaft (a Kawasaki EX-250). I knew from looking at Matt's drawing of the circuit that I didn't need both of my bike's coils connected to the OPTOIN+ because of the wasted-spark nature of its ignition system. So when I installed it on my motorcycle I only hooked up one coil (just used one diode and one resistor). I knew this would work on my 2-cylinder because its wasted-spark ignition system fires the plug every time the piston approaches top-dead-center, which means that only one coil needs to be hooked up via the 'diode and resistor' circuit to provide the correct RPM.

I've never worked with an inline 4 cylinder motorcyle engine like your CB engine, but now that I've read your latest post I've realized that for a fuel-only Microsquirt application you need to do the same thing that I did. Reduce the circuit to only one coil and it'll work perfectly. Because a wasted-spark inline 4 fires its plugs exactly the same way as a wasted-spark inline 2.

I think that Matt_gsxr was working on a motorcycle engine that was coil-on-plug and therefore wasn't wasted-spark so he had to pick the correct two of the bike's four coils to hook up with his 'diode and resistor' circuit to get an ignition event indication to the OPTOIN+ every 360 degrees of engine rotation.

Sorry about the confusion caused by the diagram.

There's no doubt that going back to a single coil hookup only version of the 'diode and resistor' circuit for your OPTOIN+ ignition event signal is the right thing to do because as I was saying in one of my previous posts the perfect, gentle square wave it generates is far superior to trying to tame all of the coil's ugly electrical spike-and-ring with zener diodes and resistors, etc. You might be able to get it to idle well on that type of setup but getting a reliable, full rev-range is very problematic.

HaHa! I think that everyone on the forum has a different story to share on how they got their input triggering sorted out! Modifying circuits, adding components, make a wish, say a prayer... anything that will make it work. But that is the purpose of this Megasquirt stuff afterall, isn't it?

So here is my story: As EW allready knows -we have discussed a bit in another thread- I have applied the Matt_GSXR circuit following EW's advice, in my SUZUKI BANDIT 400 fuel only conversion. In the beginning I used to trigger off both coils (the B4 has an I4 engine) exactly as shown in the schematic above. The thing is that -for a reason I never actually understood- I was getting a correct RPM signal while I would expect get double RPM (since there would be an ignition event every 180deg, correct?).
Anyway bike was running like this for quite a while but I did come accros some issues that were resolved one way or another. For example there was a strange "hickup" around 5500RPM which was eliminated by changing from 2squirt/alternating to 2squirt/simultaneous. The engine would rev all the way up to redline (approx 14.000) and some issues on the high RPM area, could be attributed to poor tuning of the VE table at that area and AE stuff.

The thing with triggering off both coils was bugging me, so I disconnected one coil (the one which fires 1&4) and used only diode+resistor on the other coil (BTW this the coil from which bike's tacho receive its signal too). Started up the engine only to find out that TS reads half RPM than actual (bike idles at 1300RPM, TS shows ~650RPM). Divided the RPM bin values at half, set to 2squirt/simultaneous but also had to double upper req_fuel so that the bottom req_fuel would still be same as 2squirt/alternating (6ms) and the engine worked much much smoother than before.

Then I reverted to original tach pickup connection from both coils to see if it was a matter of req_fuel and injection staging issue rather than tach input signal. Doubled up the RPM bin values and kept other injection settings the same. Started up the engine and it was running pig rich. Tried different req_fuel values, messed with the VE table and other settings but it just would not run as smooth as with one coil triggering setup. So I reverted to that one. So currently microsquirt thinks that the B4 redlines at 7000, while the engine actually revs at 14000!

Whatever works best, but I still don't understand why it reads half RPM (unless the engine does not fire 180deg apart).

Ha!..yes it sure seems like there are so many different ways to get the elusive trigger signal and many, many ways to not get one? Each engine is like a snowflake..........

When I did my first fuel injected bike (the blue one) to get the trigger signal I initially used a diode on each coil signal side and no resistor. I had a nice tach signal right off, but it was reading twice as high as it should be...easy fix back then was just to tell the controller that this is a two cylinder four stroke engine....and it worked and I had the engine running nicely and showing the correct RPM's. I later just took the signal off of one coil (still no resistor) and changed the programming to a four cylinder engine. This engine has been running nicely for three years now....no resistor...no diodes.....just two wires going to the microsquirt controller...one to the coil and one to ground.

With this newer version of microsquirt it made no difference in changing the amount of cylinders to change the RPM readings relative to the trigger signals?