Random rpm dip
 

I'm stumped in trying to figure out my problem. I've spent hours and hours searching to not find an answer. I built a ms1 v3.0 as per the instructions on the miata turbo wiki site, actually a buddy of mine did the same thing. we built our's exactly the same as per the site and have the exact same rpm dip randomly. I tried running a set of dedicated grounds from megasquirt to the engine block and I still have the Issue. I have up a datalog with the problem showing up at record 4667. I hope someone can give me an idea on what to try for both myself and my friend with the same problem. we are running .029 firmware and have the .1uf capacitor on js8 and ground. Thanks for any help. I know my tune needs work but I have been focusing more on this problem for the time being. Next will be cold starts as the morning are getting colder here in nepa.

I assume that this is associated with an actual stumble of the engine?

yes, sir

I looked through your recording. It doesn't look like the engine stumbled, just the RPM signal went out of whack. Saw discontinuous excursions both high and low at 4357, 4658 and 4667. If the MS had reset, you should see similar discontinuities in other signals. When I've had this, I would see it in PW and CLT in addition to RPM.

Of course, you would know if you stumbled because you can feel it.

Anyway, I would remove the coil, make sure the coil bracket is good and clean, and then remount and torque. It's important for the coil bracket to have a good ground to the engine.

I also saw some parts of the log where you were near 10psi with a 14:1 AFR. You want to avoid that. Maybe be gentle until you get fuel sorted.

Let us know.

Thanks! I'll try cleaning up the coil bracket and see if that helps. As for my fueling that has since been taken care of. This is an older datalog that I posted because it clearly shows what is going on. The problem doesnt always seem to happen. some days I can drive around for hours without a single hiccup so to speak and other days it will do it almost exactly every time I cross over the 3k-3.5k rpm range. It seems to happen most often right at about 3100 rpm.

If it's repeatable and you're sure about your grounds, then it's time to use those logs to find exactly what's happening. There's a wealth of information there. What you're looking for is electronic noise, such as when the electromagnetic field breaks down in a solenoid or relay.

I am surprised no one has jumped in and said this, but this problem is pretty common if it is what I think it is. The CAS signal craps out intermittently and causes spikes. Does your log show random 10,000 or so RPM spikes even tho your engine obviously isnt doing that? (i dont have any MS software on this computer). I added the cap and it helped a bit, I added separate 10 ga grounds from the battery to the MS to the back of the engine to the front. This also helped.

I still randomly get a stutter. Mainly on highway cruise. I am not sure what I can do to get rid of this problem 100% either.

My setup is in my sig.

I do get random RPM spikes in the datalog, not to to the level of 10k more so around 6-7k. I also have rpm dips showing in the datalog where it will abruptly read 2-3k rpm lower. So what I really should do to get rid of this is make a 36-1 wheel and trigger and ditch the CAS?

is the cas the problem??