1999 Miata Flyin Miata turbo with MS2. Track only car, 1st session beat the crap out of it and ran great. Second session a few Laps in and starts to miss. Then pull into hot pits idles great, revs fine. Take it back out and under heavy acceleration shortly thereafter starts to miss. Third session set up data log and a few laps in starts to do it again. Loaded data log to Chat and results were Findings Relevant to Coil/ignition Dropout Lost Sync Events The ECU recorded 61 crank/cam sync losses. Lost sync means the Megasquirt momentarily lost its crank trigger signal. That can present exactly like an ignition misfire: sudden RPM jitter or complete cut. RPM Jitter Maximum single-step change: ~6,559 rpm (!). Those are sharp, non-driver-induced spikes—classic sign of trigger noise or dropout. Dwell Irregularities Most dwell values sit near 4.0 ms, but a few samples jump to 8 ms+ when sync is lost. That isn’t normal coil control and can produce weak or missing spark. AFR Spikes AFR occasionally swings lean (up to 18.0) at the same times RPM and dwell glitch, which fits a cylinder or whole-engine misfire. Battery Voltage Solid 13.4-14.3 V, so it’s not a supply-voltage issue. 3. Interpretation These patterns point less to a single failing coil pack and more to crank/cam signal or wiring/grounding problems that get worse when the engine is heat-soaked: Your log instead shows system-wide ignition cutouts. I cannot replicate the issue at home as it is not street legal or registered, Crank sensor is obvious choice but I installed a new OEM sensor and it still misfires. Coil pack is 18 mos old. Prior to this issue, had recent clutch replacement, coolant reroute, valve cover gasket and cam seal work done at a local shop. From Chat - because the misfire only started after major front-end work and you already have visible pulley movement, the crank damper/pulley is now the most probable root cause of the heat-soak sync loss.
Verifying runout is cheap and conclusive—do that before buying anything else. Does this make sense? I measured crank and seems to deviate .3mm .

Thanks for any help much appreciated.

 

Hey there! I checked out that thread, and the heat-soak issue under hard acceleration really sounds like a classic case of intake temps rising past the ECU’s comfort zone. Once the engine is fully heat-soaked, timing gets pulled and the car starts to stumble. Upgraded intercooling or better airflow management might be the key fix.

 

Got it, 0.3mm runout could definitely cause those sync losses. Checking the crank pulley/damper alignment sounds like the right next step.

 

Cam and crank proximity sensors both hate high heat I know the cam sensor is a common issue when temps are very high. I have my crank trigger very very close like you should only be able to slide a credit card in between the crank sensor and the trigger wheel nubs.

 

gpt bot