Updated: SOLVED as of 5/6/2018 unless otherwise noted

The Problem:
- Sync Losses occur when car has been running for a while and engine is hot resulting in, wacky Tach, major loss of power, and AFR swinging lean
- Cycling the ignition seemed to resolve the problem temporarily until it would occur again, but once it's misfiring, it stays misfiring
- Logs show Sync Loss Count index from 1 to 2 when the problem occurs
- Logs show Sync Loss Reason 2 - missing tooth at wrong time

Action items, but problems persisted:
- Crank sensor was still snug, gap from trigger wheel verified
- Replaced spark plugs using a gap of 0.030" and 0.025"
- Replaced plug wires
- Replaced cam position sensor
- Replaced o2 sensor


Action items, fixing problem:
- Cleaning grounds
-Identifying the plug to the crank sensor was missing a grommet (subsequently bypassed the plug and soldering wires direct)
- Re-tightening the VVT valve cover which houses the CPS over the cam as it had come loose from track day

After performing the above, I drove around for two hours and pulled some WOT logs, and everything seems fine. Logs show zero sync loss counts.

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5/5/2018

Hey all, I'm having an issue that I haven't encountered before. It seems that my car is either misfiring, or dropping spark, or doing something that makes it bog and go lean. It stays in this state until the car is powered down, and the key is cycled. Below is an account of each time it's happened:

-Driving home from a weekend at Summit Point(8 sessions over two days) last month my car stumbles and feels like it's loosing power. AFR goes lean, I don't lay into it and pull over. I cycle the key and restart, and everything seemed fine. I drove home, all is well.

-Fast forward to last weekend, and I am out and about with the GF for a cruise. Just driving around and when headed home after a couple hours, it did it again. Each time I'd re-cycle the key and everything would be fine for a little while.

-This week I replaced the spark plugs, with some fresh BKR7E's (0.030" gap) and had then changed to a fresh set of SADFab wires that I had on standby. I also replaced the o2 sensor and the cam position sensor. I drove it around and it seemed fine for an afternoon. TODAY, I drive around and things seem fine. I pull a couple logs for 18psi and on the drive home it happens again. Tach jolts, engine sounds like it drops a coil, and the car feels under powered and AFR leans out and I pull over. As soon as I restart the car, it idles fine, and I carry on my way. It happened with more frequency in the 20 minutes it took for me to drive home, but this time I had my laptop on me.

Attached are some logs. The markers indicate the moments after it begins. I'm not exactly sure what to look for in MegaLogViewer, but I did notice a Lost Sync Count go up one at the event. Concealer had recommended that I check the electrical connections at the ECU and grounds. I plan to do this in the coming days if it doesn't rain, but what I still don't get is why cycling the key would temporarily solve the problem. Before I spend more money on replacing LS coils, I just want to make sure the logic makes sense; If it where a ground issue, wouldn't it be less intermittent and more consistent?

Any insights would be appreciated.

 

right now digging through these threads:

https://www.miataturbo.net/megasquir...nc-loss-91089/

https://www.miataturbo.net/megasquir...-insane-85036/

 

Something weird is going on with your pulse widths - drops from 2.2 ms to 1.5 ms even though the rpms/map sensor are similar. Print screen.

 

It seems to just happen right after the loss sync count indexes up to 2

 

Aidan pointed out Lost Sync Reason 2 being related to missing tooth at wrong time. It popped up in logs as of two weeks ago. I'm still waiting on a new sensor with shielded harness from Ballenger, but the trigger wheel and the current sensor is snug. I'll check the wiring and revisit grounds.

 

Attached is a Composite Log of startup.

Also just for clarification, not using a CAN module for WB o2. I did see that pop up in some threads.
Ignition input capture is set to Falling Edge.

Later in the plot, it is uneventful and smooth. Only phenomena is at the beginning which is pretty normal until the engine catches if I read correctly. It's so damn intermittent and temp related. My car may have cooled too much to capture anything meaningful. I don't want to take it on the streets again though; breakdown lanes turn into traffic lanes so I won't have much place to pull over.

 

I was about to point out the same thing: PW and DC drop and stay low as soon as it happens. When it drops rpm signal, it seems to maintain the other signals like map, tps, etc. And yes, lost sync count goes from 1 to 2

 

Just to track what changes I've made so far.

I found that the rubber grommet in crank sensor plug was completely missing. Just as a trial I soldered the wires together, bypassing the plug completely since it'll be replaced all the way to the ecu anyway when the Ballenger Ultimate Miata shielded stuff comes in.

I also cleaned up some grounds and took care of the ls coils that where rattling loose. I noticed that half of my valve cover bolts where loose which was corrected as soon as I tightened the SADFab bracket back down.

Initial start up now shows the lost sync counter at 0. Whereas in all previous logs it initiated at 1, indexing to 2 when it begins to run rough.

Ill go for a drive today, heat the motor up and see if it returns.

 

 

Yea that's what I was thinking, but didn't know how much static clearance it loses. It also seem to only get worse when it was hot. Think thermal expansion and that little bit of Gap would be the culprit?

it corroborates the story as it happened after the track day, on the way home, but not during so things might have loosened up to the point where it would systematically get worse over time as it continued to loosen.

 

 

I set a gauge in Tuner Studio to display lost sync counts and after two hours of driving, and two hard WOT pulls for logs, I parked the car with no problems. I am reluctant to call this solved until it gets hotter out....but between cleaning grounds, dumping the janky crank connectors, and tightening down the valve cover (as a byproduct of re-fastening the LS Coils) everything is operating smoothly.


I'll update the thread if anything negative happens, but the first post will be amended to reflect our hypothesis.

 

I’ll send next map tomorrow