tach signal while cranking

[racincrj]

I have a abnormaly long crank time before i get rpm it does fire up and run. i feel like its something to do with my configuration settings?
what i am working with is a cb750 sohc with single vr sensor 12-1 tooth wheel, wasted spark configuration. any help would be awsome!

[24c]

Hi
Can you do a datalog? It might be a battery voltage issue, maybe you're getting a reset.
Long time before getting RPM, could also be a VR voltage & starter speed related issue?
Which MicroSquirt are you using.
Some guys can kick start their projects into life, so you obviously have an issue.

Mike

[racincrj]

Hi Mike

I am running a v3 microsquirt with 3.77 code. I would love to be able to kick start it but dosen't seem to pick up a trigger signal until around 300 rpm.
it does start and run quite well. but alas the starter clutch is staring to go. any input would be awsome!!!!

Curtis

[24c]

Hi Curtis,
I can get cranking from about 49rpm onwards with a v3 and a Hall. I suspect that the VR isn't generating enough voltage until 300 rpm. I am stuck in a car park working away from home, so as soon as I get a chance I look at the datalog.

Do you have any pics of the trigger wheel VR arrangement? Can you decrease the air gap, as this will boost low speed RPM detection. The VR circuitry in the v3 should take care of the over voltage at higher RPMS.

Mike

[racincrj]

i had scoped this setup on the bench and was happy with the pattern and wasnt really paying that close attention to the low speed voltage. i am gonna do some more testing, this is a wheel speed sensor from a chevrolet truck and the teeth match the sensor quite well. i was hoping to make this work because it was free!
and it fit good it the points cover.

[24c]

Did you get anywhere with a low speed test?

[racincrj]

Well what i have done is found a 24 tooth wheel and a matching vr sensor from what i think is a mitsubishi automotive distributor. the motorcycle does seem to start better. however still no signal at below 300 rpm. so i have tested the new sensor at kicking speed it puts out .5 volts ac. at 300 rpm it puts out 2.0 volts ac. not sure if thats good or bad? maybe a better way would be a hall sensor? like i said it does seem to start better now! about 1 second in and it has rpm signal and fires up shortly after. i can live with it this way for now and maybe upgrade to a different sensor at a later date.

[24c]

however still no signal at below 300 rpm. so i have tested the new sensor at kicking speed it puts out .5 volts ac. at 300 rpm it puts out 2.0 volts ac.

That is indeed the problem, you need a minimum p-p voltage to register with the MicroSquirt. The older MicroSquirt aka v2, had a 1.8V threshold on the VR2IN input, and this caused me no end of problems with a soft tooth pattern like a cam lobe. The only way to overcome this was to reduce the air gap to next to nothing, but when the engine was warm the cam lobe was hitting the sensor.

like i said it does seem to start better now! about 1 second in and it has rpm signal and fires up shortly after

Are you saying it has RPM as soon as you touch the starter and then fires up about 1 sec after seeing this, or it takes 1 sec to see RPM? If it's the first one, it sounds like you have to tweak your fuelling slightly.
Can you see any RPM when kicking the bike over?

Have you tried to reduce the gap further and see if this lowers the RPM detected? The newer MicroSquirt has much better VR conditioning circuitry and it works great out of the box. I've never had an issue with cranking RPM with this unit, and Tunerstudio starts at less than 50 rpm no problem using the B&G firmware.


Mike
BTW The other trick I did to boost voltage to aid cranking rpm detection with the older MicroSquirts was to add embedded magnets in an aluminium disc to create a simple trigger wheel. This was because I was playing with a Renault Clio VR sensor that I didn't know was faulty, when I changed the sensor I didn't need these. When I used a Hall sensor it was like night and day, however VR sensors are more robust in hotter environments. Hall sensor especially the later multi transistor discriminatory types can fail quicker due to vibration & heat. I've not had any problems with this yet, but I have been using these long enough in a running engine yet to test this out.

[racincrj]

No I see rpm after about one second of cranking with the starter. I do not see any rpm while kicking the bike at all. I will try to lower the air gap to see if it helps.unfortunately won't have a chance to get back to it for a week or so. I will let you know how it goes thank you for all your help!
.