Speeduino is now on Github Sponsors (Rather than Patreon): https://github.com/sponsors/noisymime
Any general discussion around the firmware, what is does, how it does it etc.
By Dave3891
I have a LS engine with a 24 tooth stock crank wheel and a 2 tooth cam wheel.
For some strange reason the GM 24x pattern runs really rough and backfires, but if I use dual wheel 24 tooth and both on falling edge it runs great, but it shouldn't.


I have it set at 24 tooth and both are falling trigger, so based on the diagram it should fail sync should it not?
Looking at the diagram 48 teeth would pass between the 2 cam falling edges?
So it acts like the cam trigger is using BOTH for a setting, but I can't find anything in the code that would allow this.
But the GM 24x trigger setting uses BOTH for the cam and it doesn't run good at all so I am a little confused here.

I would think the dual wheel setting with 24 teeth and falling edge would give a constant stream of failed sync counts, but it doesn't for some reason.

Attached is a log and image of my trigger

Just looking for some insight on why this is working as it is.
(74.96 KiB) Downloaded 42 times
trigger.JPG (119.65 KiB) Viewed 691 times
By noisymime
I've actually been meaning to pull out the 24X pattern for essentially the exact reason you've discovered: It's not needed.

If you look at the RISING edges of the cam signal they vary significantly, however the FALLING edges are actually perfectly evenly spaced. It doesn't look it, but those FALLING edges are all exactly 15 degrees apart.

I've had a few of these running and they all run fine with dual wheel and falling edge, just like you've discovered.
User avatar
Correct. If you look at the two graphics posted above, you see one cam "tooth", with one rising and one falling edge in 720° crank degrees. The 24 is per 360° crank rotation, and the 1 per 720° cam rotation or cycle. Bingo, a straightforward 24/1 teeth per-wheel dual wheel setup.

For others reading that may have different sensors or signal conditioners in their setup, the falling edge of the physical teeth is what we are reading in this example, in order to read the tooth spacing and angles properly. This edge may read from different sensors as rising or falling voltage, and various conditioners may pass it straight through or invert the signal. Keep track of what the signal is doing on what edge by the time it gets to the processor. ;)

By Dave3891
Ahhh, Ok I think I understand it now. I wasn't thinking of the cam falling edges in terms of 720 degrees (Full engine cycle).
And looking at the dual wheel code more it makes sense on how it works.
The primary tooth interrupt resets back to one every time it gets to 24 no matter what and the secondary tooth interrupt checks to see if the tooth count is 24 when it is triggered (Even though 48 crank pulses have passed).
I was thinking that the primary tooth count would only be set back to 1 when the cam edge was triggered (making it 48 at this point)

Thank you all for your input I have the simulator[…]

ECU for my Three Wheeler Project

Hi Maverick As you said, you should be ok with […]

Sharing of tunes is NOT recommended. Different fi[…]

Trigger wheel setup help please

Wire it for semi-sequential. That way if you add […]

Still can't find what you're looking for?