No RPM signal in Megatune

[CSM]

Hi everyone,

So I've got all my Yamaha sensors calibrated and hooked up to my Microsquirt, and made a base tune. The first time I powered it all up and connected to Megatune, all sensors looked good except TPS, which didn't appear to take my ADC values, and the crank position sensor. I did some searching, and found I needed to update my code in the Microsquirt and the megatune ini. I did all this and the TPS works perfectly now, and I'm getting no warnings when I burn an .MSQ to the microsquirt. But the RPM gauge still showed nothing. It is stuck at zero, not even giving incorrect data. I checked my wiring, the CPS is a VR sensor (a little Nippon Denso unit?) VR+ to 32, VR- to 33. I put a scope on the VR connections at the 35pin amp connector and the waveform looks fine, exactly like the one on the VR sensor page of the manual. I'm not sure why Megatune is not displaying a tach signal. Is there something in the configuration that could cause this? It seems like it should be something simple, having absolutely no signal show up. Here are my crank trigger specs.

12-1 trigger wheel on Yamaha 50cc 4 stroke.
24 skip teeth
no dual spark
using uS coil driver

I've attached a copy of the msq. This is the one I'm copying over for the later code version(Im sure there's a better way to do this) so I haven't added warmup or accel enrichment yet, but the core's there.

[Matt Cramer]

The number of skip teeth cannot be more than the number of base teeth. Try telling it you have 12 skip teeth and a 2 cylinder engine.

[CSM]

So I tried this, and nothing. I tried 4 cylinder with 6 skip teeth as well. It almost seems like an issue with the data transfer throught the usb/serial adapter to megatune, but in the same note, I'm not getting any injector pulses either. I tried injector test mode to make sure it was wired up fine and worked, and everything seemed normal there. As far as data transfer, all the other sensors display just fine, but from my experience, engine speed is the largest piece of sensor data transferred, so maybe that's a problem. My next step might be pulling apart microsquirt and do some signal probing.

[CSM]

After awhile, I decided I would plug the opto wires back into microsquirt to see if I could get an RPM reading with a function generator. I set up the function generator with 0-5v square wave, changed the 12-1 trigger wheel spec in megatune to a 12-0, 2 cylinder, 12 skip teeth, and after a few reboots, an RPM showed up. I could adjust it with frequency, and the injector pulsewidth seemed to be working properly. Cranking speeds showed cranking pulsewidth, accel enrichment came on at specified Tdot, etc. However, is would get stuck at zero fairly often too, like whenver I left the RPM sit at 100 RPM or so, it sometimes drops to zero and won't come back online until I reburn the ignition settings or reboot microsquirt or both. Also, I put a scope on the injector, and most of the time no pulses showed up, which i assumed was normal since there was no missing tooth and therefore no way to trigger when to inject, as far as i know. One time, though, the injector pulses did show up, the correct width and everything, but I'm not sure why.

Anyway, as far as the VR Sensor goes, I would sure like to get it to work, and if the opto sensor works, I don't know why the VR wouldn't. It just goes through some pretty robust circuitry. I guess now that I know the processor reads things right, I'll experiment with some more values. Do you think It could be related to the speed I'm testing at? I've only tried cranking speeds with the VR so far.

[24c]

Have you tried reducing the VR sensor air gap, my Nippon Denso sensors were very sensitive to air gap with the MicroSquirt, yet the Yamaha ECU had no problems picking up the AC signal. I couldn't always get rpms at first.

[CSM]

I checked out the air gap on the vr sensor, it is about 1mm. the bracket has spacers so that you cannot move it from its original mounting location, but that could be easily changed...Before I thought about doing that though, I found out about tooth analyzer, just what I need I though. First, I hooked up the hall input, my function generator square wave, and it showed up just fire. Then I hooked back up the VR sensor, and nothing showed up when cranking. Then, I ran a sine wave into the VR input, from what I can tell, this should work to at least bring some sort of square wave to the processor, since it runs through a schmitt trigger and comparator (I think). I set it at 15vpp, and once again, nothing showed up. I think my VR circuitry may be dead...If all else fails, I think i will make an optical trigger wheel.

Also, about the injector not firing with RPM signal, does it make sense to anyone that It wouldn't fire using only a 12-0 toothed wheel input, because of lack of a way to index? I thought that made sense to me, but then I thought about the stimulator - I'm not sure about this waveform, but I think its just a square wave, yet it pulses the injector LED's.

[CSM]

After I realized the stimulator uses default mode, I tried the default mode, which is distributor pickup. This worked great. RPM responded quickly and never got stuck at zero. I had the injector and spark plug going, shocked myself in the process. I'm pretty sure the injector wasn't firing earlier, because the Accel and warmup LED grounds were shorted together, apparently that does it. In short, I think I need to implement an optical crank sensor, either with an M-N wheel or distributor-type pickup, which is probably easiest. The only thing i noticed when this worked was that megatune freezed up more often, but thats probably not a big deal. I'm not too worried about dirt contamination.

[24c]

I checked out the air gap on the vr sensor, it is about 1mm...snip

I was running down to 0.3mm on a cam lobe (VR2), and 0.7mm on the crank (VR1), so it might be worth trying the spacers. I observed the smaller the air gap the lower the rpms were detected in MegaTune/TunerStudio. It was the cam lobe sensor that was the most problematic in my case, as I couldn't get a sync signal until 950 rpm, but I still think you'd see benefits on your cranking rpm if you reduced the air gap.