Another Sync Loss Issue
 

Today was a huge moment for me. After months of time along with blood sweat and tears I have finally completed my forged VVT project (kinda). Maybe I'll make another post about that journey in the general chat forum.

My issue is that I lose sync when I try to change rev any faster than maybe 100 revolutions per second. I can idle and I can cruise but that's it. Another caveat is that I can't cruise past about 2,300 RPM. That made it very difficult for me driving my car home from my welder's shop. When I try to rev it's similar to hitting a rev limiter except at 2,300. I see the sync loss counter climb to 10, 20, 30, 40 all within seconds of trying to rev. It doesn't die though; It catches sync instantly when I let off the throttle. Strangely, I get 0 sync loss events when it's idling or cruising below 2,300 rpm. Another strange thing is that there is no difference in performance when I unplug the cam sensor from the ECU so I'm guessing that's the beginning of my issue.

I'm running the same MSQ that I was running when I had my 1.6 going except for the difference of required fuel and wheel decoder (Miata 36-2). I have a 36-2 trigger wheel in there from FM.

I checked my lines throughly. The same ground that went to the 1.6 CAS goes to both the new cam and crank sensor. The same 12V that went to the 1.6 CAS goes to both the new cam and crank sensor. White went to crank. Yellow/Blue went to cam.

Any idea on where I should start to diagnose this issue? Short of replacing that cam sensor I'm pretty stumped.

You need to post a log of the sync loss.

I had to run a VERY small gap between the crank sensor and the FM 32 wheel. I had to be as close as like.005. I sanded the paint off the ends of the nubs, that seemed to help also. That will have other effects later on though, like rust.

Gotcha. I attached the file to the first post.

I'll get to sanding and moving the sensor in closer right now. I'll post a log of that change afterwards.

I assume you're running batch injection. That would explain why the cam sensor makes no difference. Miata 36-2 can run batch on crank sensor alone.

Sync Loss reason is 2. Missing tooth at wrong time.

Post your tune. If your settings are correct I think you just need to tune your pots.

Here's the tune.

I was able to rev the engine to 3,200 rpm this time before encountering the sync loss after sanding down the paint on the teeth and moving the sensor in to .005

Which ecu, exactly?

DIY MS3X

I wired my MS3X following along with the guide on Trubokitty.com and I don’t remember a difference in how the pots are configured between the original 1.6 setup and the VVT setup.
How would you recommend I tune the pots?

I'm assuming the sensitivity pots need to be adjusted.

NB setups tend to need more of a clockwise rotation of NA setups. if anything R11 tends to need 4-5 turns.

really need to see a composite log in order to accurately diagnose. As lost sync 2 is typically not a pot related issue.

which make sme think you have the wrong trigger settings -- id switch it to falling and inverted. again the composite log would help here.

At 4-5 turns what should the resistance across the R11 potentiometer read?

Also, attached in the composite logger with Falling Edge and Inverted settings. It didn't fix the issue.

https://cimg3.ibsrv.net/gimg/www.mia...7aff8f9614.png
https://cimg9.ibsrv.net/gimg/www.mia...53dc3a95ea.png

Looks like my ECU is finding a missing tooth where it shouldn't be when I get up to about 3k rpm. Any ideas on how to remedy this?

I'd adjust the mainboard pot a half turn CW at a time till it goes away through redline.

nice work, and I learned something today.

Worked like a charm! Actually, turning the pot on the mainboard clockwise made it worse so I turned it the other way a few times and to redline she goes.

Thanks Brain for all the help you do for the Miata community! I'm certain that you've helped thousands of Miata owners with zero obligation to any of them. I just want to let you know that your wisdom is very much appreciated. Arigato Brain-senpai!