Extra teeth only at specific RPM

[nismoryco]

Hi,

I am running a Microsquirt V2 with the latest firmware. My engine is a 4 cylinder wasted spark with a 36-1 wheel and a Ford VR sensor. The problem that I am having is that the uS is receiving extra teeth (fairly rapidly) only at ~3200 RPM. Either above or below that speed the trigger signal is fine. I am also not getting any timing resets. I have played with sensor gap, but it hasn't really changed anything. The sensor is currently at 0.019" and I have tried various gaps to about 0.060". At large gaps, it takes longer to sync during cranking and sometimes there are timing resets (especially when the engine is cold). I am unsure of what to try next. Thanks.

[24c]

Hi
Based on my experiences to date, there must be noise on your ground/negative somewhere creating the "extra teeth". You should post a datalog, there might be something that others can interpret.

[nismoryco]

Here is a snippet of the problem. It counts up pretty quickly, but I do not get any resets and I can't notice it in the car.

[grippo]

I think what is going on is that the 2.890 code has a patch for when an extra tooth comes in. This can be caused by the signal from the area near the missing tooth, which has a small hump in it that is just over threshold, usually starting at a certain rpm. Your case is unusual in that it only occurs near an rpm rather than above an rpm. If the threshold is raised, this may help, but it could also cause hard starting as you experienced when you increased the gap. The code is sensing the extra tooth and is throwing it out. Bruce was bale to rev his 4 cylinder test engine to 13000 rpm by using this fix rather than messing with the VR circuit. So as long as you are not losing synch and not feeling anything in the car, everything should be fine.

The only other things you can do are play around with diodes, resistors in the VR circuit - a lot of people have done this and documented what they did; get an LM1815 add-on board; try a different sensor, especially if the wheel/ sensor combo is custom and not OEM; try a Hall sensor. We have spent a lot of time on this and have a long range plan to solve the problem, but it isn't an easy one and will take time.

[nismoryco]

Thanks for the replies. I have tried a different sensor. The first one that I used was the VR sensor from a Subaru. With that sensor, I only had a problem during deceleration from the engine redline. All other speeds were fine. What would the difference be in the two sensors that would cause the difference? I will have a look at my trigger wheel to make sure there are absolutely no bumps that might be interpreted as a tooth. I will also do some research on some of the mods that others have tried.

[nismoryco]

I have done some testing on my sensor/setup over the weekend. I hooked my scope to the vr input of the Microsquirt and measured my signal. The wave looks clean above and below 3000 rpm. Right at 3000 rpm, I get a small hump in the missing tooth that is causing the false trigger. Changing the sensor gap only moves the RPM range around. I also tried a different trigger wheel (36-2), but got the same results. Also, I made absolutely sure that there are no burrs or anything in the missing tooth region that may be causing this problem.