Hey guys, really struggling with this and looking for some insight into this misfire/sync loss I'm getting at high RPM (often right around 5k but sometimes anywhere 5-7k). Apologies in advance for lengthy post and lots of logs. Car is 92 chassis on MS3ProPnP with stock NA VVT engine swap last fall per megathread running VVT coils, injector harness still stock (batch) fueling. Had no issues all spring/summer and everything felt very good until my 2nd autox (set up on a 1.2 mile track) where I started having this issue a few times and now has gotten worse, happening probably one in every 3 pulls. Can replicate revving stationary in neutral as well but is much less frequent. My tune is a combination of DIYautotune 90-93 basemap with 01-05 changes once VVT engine was swapped in. Only changes have really been to the idle and VE table. My subharness I made includes vvt/cam/crank and goes straight to OEM CAS wiring connector, VVT shares this 12V feed as well, with the VVT control wire running in that harness then to MS3.

Please see attached tune and logs and/or screenshots, it's very clear where the sync loss is occurring I just can't figure out why after a few weeks of testing and really don't want to miss my track day next weekend. I am seeing extra pulses/noise from one or both cam and crank which makes me suspicious of wiring, especially happening first at the track, but can't find why or get them to stop. I don't see any noise in other sensors in my data log (besides VVT but is that just since it's losing sync?) but I'm new to this so definitely could be missing something.






Things I have tried (in order) with no improvement

• checking all wires/connectors, added ziptie to cam sensor connector
• new NGK/NTK cam sensor from Rockauto
• adjusting crank sensor gap from spec, further gap may have helped frequency a bit but not positive
• New NGK/NTK cam sensor from Rockauto
• unplugging VVT solenoid
• checked base timing and that pulley markings were at Cyl #1 TDC
• checked grounds
• cutting/isolating "extra" black and green ECU sensor ground at intake manifold that I read helps noisy signals on NA6 chassis. (no change that I saw)
• pulling cam/crank/vvt sub harness (was routed along fuel rail under intake mani) to further inspect, no findings
• re routed sub harness above intake, secured extra well with rubber insulated clamps
  • this seemed to help for some pulls that night but the next day was just as frequent again
• tried enabling noise filtering stuff in TunerStudio, (previously had none, just the global "4" from basemap)
  • I don't really know what values to put in the boxes or what I should have so they could be way off

I tried to figure this out myself but I've exhausted all my ideas at this point and nothing I found in other posts fixes my problem. I feel like I ruled out the sensors themselves since I'm seeing it on both cam AND crank, and there was no change with new sensors to either. Do I need to drop the money on new OEM sensors? Original CAM sensor was OEM and put that back in once new one didn't help. Ballenger Spec Miata OEM CAM sensor w/ the potted pigtail? Fluidampr and 32 trigger wheel?

 

Triggers are normally shielded, are yours? Although I’ve seen plenty of installs without perfect shielding have no issues. Am I reading that correctly that you tried a larger gap? I’ve needed smaller gaps, but usually with a 36-2 wheel.

 

They are not shielded, I was under the impression from everything I could find online that NA/NB doesn't have shielded triggers for cam or crank from the factory, am I wrong on that? Haven't seen it as a necessity on here so I figured it would be fine, especially not running near the ignition wires. I know it was working fine for a while but I am kicking myself now for not shielding them to rule that out, I didn't want to run new ones all the way back to the MS since I utilized as much of the factory wiring like discussed in the VVT swap megathread.

Correct, for crank gap was/is right around the middle at 1mm gap but I tried closer to .5mm and further to 1.5mm. Further seemed better for a few pulls but then still got noise so again could have been a coincidence. I was figuring since I was getting "extra" pulses rather than "missing" pulses further could be better but when I tried a bit more past spec it was too far to read anything. Also I was going to wait to put a fluidampr and 36-2 on the built engine going in ~soon~ but this has delayed me.

 

For the ~$40 for the stock trigger wheel, I’d go that route and see if it helps. You can always sell later and only lose $20.

i may be thinking of the shielded o2 sensors rather than triggers

 

I do seem to remember the o2 signal wire being shielded, I thought that was the only one. Also to clarify I have the OEM trigger wheel right now, bone stock VVT engine from 01. I will probably go ahead and order a 36-2 now since I was getting one for the built engine anyways, just a pain to swap it onto this one just to test. I was thinking it couldn't just be crank related since I'm seeing noise on the cam signal as well.

 

I'd also only ever get OEM crank sensors. Or so I've been told. Just not worth the hassle with OE sensors.

 

I probably should have dropped the money on them just also wasn't able to get them as quickly and have had good luck with NGK/NTN in the past

 

Okay, completely new theory (hopefully not too stupid)- is it possible my electrical noise in cam/crank is a symptom CAUSED BY a misfire, rather than the noise CAUSING the misfire? The first time this happened at the track it was very subtle hiccup at WOT, barely affecting my autox runs. At this point it's often a pretty violent misfire, tach bounces down like hitting limiter and car hesitates a good bit. Aggressive enough that I feel bad doing it to the car and won't drive it besides testing. Is there any definite way to differentiate which is the cause vs effect?

I originally thought (before logging or anything) it was ignition related misfire so pulled plugs but they looked fine. Iridium long life DENSO SK16PRL11 gap right at .044 spec. Should I try new (or different) plugs or maybe even just tightening up the gap a tiny bit? I could try to find someone nearby with VVT coils to test those?

 

I am having similar issue but only when engine is good and heat soaked, then it starts missing badly. I did install an OEM crank sensor and regapped. Also have an MS2 with my turbo. Loaded MS data log to Chatgpt and response is as follows: since you’ve already put in a fresh OEM crank sensor and set the gap, I’d pivot to signal integrity and input conditioning rather than the sensor itself. Your log’s pattern (lost-sync count climbing, huge single-step RPM spikes, and brief dwell surges) still screams “trigger signal getting noisy when hot.” Here’s a focused plan that separates trigger noise from actual coil failure and tells you exactly what to check next. Not sure if yours was a heat soal issue or just intermittent.

 

I originally believed heat related since it happened at the track for the first time, would do once or twice per run. Only happened once on the drive home on the highway, then once more that evening, now pretty much constant regardless of temp (although I'm letting it get up to operating temp before a pull so it's not stone cold of course)

 

mine is definitely heat related. I can hammer on it for one full 20 min session and all good. 1/2 way thru second run it starts missing under hard acceleration

 

I had sync issues when hot on my 01 track car... chased fuel. Chased spark... Finally swapped sensors.

MS3, fluidamper/36-2 wheel. Crank sensor I put on when I rebuilt was a Beck-Arnley(not cheap, but not $150 OEM either). Cam sensor was also a Beck Arnley(I think), but it was a Mitsubishi sensor(same sensor the Ballenger setup uses).

Swapped to a Ballenger potted cam sensor with the deutsch plug. I guess they have figured out that constant high heat actually degrades the OEM wiring plug. Also swapped in a brand new OEM crank sensor...

Had to change MS3 from falling edge(with the Beck Arnley) to rising edge for the crank sensor and reset base timing. My tuner thinks the aftermarket sensor was either wired backwards or is just a poor copy of the OEM sensor. Havent had a single issue in 2 years since I did the Ballenger sensor and a brand new OEM crank sensor.

I feel for these cars that run a lot of high RPM, that the 36-2 wheel is imperative to keep a good, steady crank signal. I think a 36-2 will also tolerate a bit more gap variation because you have so many more pickup points.

 

Linking a couple videos from last night's testing to show how aggressive it is usually.

• Tried a ghetto "shielding" by wrapping the whole cam/crank/vvt sub harness tightly in aluminum foil. No change whether shield grounded or ungrounded.
• Tried unplugging VVT solenoid again, both at solenoid and signal end to ECU
• Tried running Trubokitty ignition basemap for 90-93 (less aggressive than DIYs 01-05), no change

In the chance that it's a misfire casuing noise not other way around I'm grabbing some new NGK BKR6E-11 on the way home from work to rule out my plugs, as well as try a tighter gap. Then will try and find someone nearby to try their OEM VVT coils. Maybe CAM sensor as well.

https://youtube.com/shorts/jsstYvTZRxU?si=Lh_Iz8uCWZnZ5k__

https://youtube.com/shorts/T9loVVsA5sc?si=mZDjC4u5kci6s0vC

 

Interesting, did it look like the videos I just posted? I should probably fork up the money for Ballenger and OEM crank to rule that out. I am running falling edge though since that's what I had seen to run, are you saying you're running rising edge now?

 

I have no logs. First time it happened was about 12-13 minutes through a session on a very hot day here in Texas. Limped off track. Let everything cool for 2 hours and the car fired right back up so I went out again and made it 10 minutes... Wasn't suspecting sensors as they were new, so I put new coils and plugs on the car. Next event car ran great all weekend until the cool down on session 4 of day 2... Sync loss and barely got the car around and it died on the hot pit... Car was dead as a door nail. Guy there says put new oem crank sensor and a Ballenger cam sensor setup... Cam sensor came in first... Car still dead. New oem crank sensor showed up... Car fired up but wasn't happy. Called my tuner and he says "I had to change that other sensor to falling edge to get the car to run initially, change it back to rising edge"... Car was immediately happy. He said reset base timing offset... 7 degrees off which made sense due to tooth width... Zero issues since.

I believe rising edge is the preferred from what I remember reading. On the stock wheel might not matter as much as the **** are so small... But on a 36-2 you have wide teeth so the edge is much further apart... 5-7ish degrees I think(I did the math a few years ago) and can really jack with the timing.

Everybody that I know that has gone to a 36-2 has reported much smoother power delivery. You can do a 36-2 on the stock pulley I believe. That plus a new oe crank sensor and the Ballenger potted cam sensor setup is where I would start... Especially when you are saying you suspect it's heat related.

 

Got it okay thanks. Mine drives around perfectly fine besides hard accelerations 5-7k where it consistently momentarily sees an extra cam and/or crank pulse which is why I'm nowa bit suspect of an ignition related misfire causing noise.

I do have a 36-2 trigger wheel on the way, but I'll try rising edge with the OEM trigger wheel tonight just in case that helps. Trying not to fire the parts cannon too much but ballenger cam/oem crank would be next on the list.

 

This.

 

Alright bumping this again with some more info from the past few weeks. New plugs did not help at all, and tightening up the gap from .044 to .03 or .035 actually made the car idle terribly, i had to rev it to keep it from dying. This made me highly suspicious of something ignition related since i thought they should run .025 to .03 gap that alot of turbo guys run on stock coils. Couldn't find any local guys running the NB2/VVT coils so I just ordered a couple used oem ones from Ebay, figured for 20 bucks worst case I end up with some spares.

Threw the 2 new (used) OEM VVT coil packs in, and car ran beautifully. Did probably 20+ pulls that night, not a single misfire, hesitation, sync loss, anything, even seemed to be idling better. Drove it to work the next day since I was glad I ~fixed~ it finally, and then suddenly that morning another misfire, then another. Another couple on the way home, and its right back to how it has been the past month. Thought I must have gotten crazy unlucky and killed a coil pack already, so got a couple more but same issue with the new set-and just about any combination of 6 coil packs I could keep track of.

What gives?? I went from not being able to do 3 clean pulls to getting 20+ in a row flawlessly, only change being the coils so logic tells me this HAS to be ignition related but not sure what else to do. Open to any suggestions. I'm about to give in and order R8 COPS and wire it up sequential but hesitant to introduce more variables.

Note: I have supermiata 36-2 trigger wheel in hand now, have not installed yet since every time it misfires I'm seeing one singular noise pulse in both cam and crank signal (at same time) immediately before each sync loss. I don't think it's possible for this to be a sensor or resolution issue but educate me if that assumption is incorrect.

 

So from reading this, when you installed the VVT engine you swapped out the cam position sensor which is normally on the rear of the exhaust cam(92 chassis) and wired in 99+ sensors.

This is a bit of work, but if you still have the old cam position sensor you could install it to see if that solves the problem.

I looked on you tube trying to find what the tach normally does with a high rpm misfire and ran into this video, where the guy had a misfire and basically
replaced everything, only to find a connector that was not properly plugged in.

I think the only things you have not double checked on the cam sensor inputs would be the input wires themselves and the MS3 computer/connections?

I have a 91 and had one of the wires fail from the cam sensor to the CPU. The car would occasionally just die and then restart 10 minutes later
-no misfire though, but you never know the exact nature of the failure.

 

did you mention what you're running for dwell times?