2004 MSM with RPM-based P0300 (no misfire felt) - Miata Turbo Forum - Boost cars, acquire cats.

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Old 09-11-2016, 07:14 PM   #1
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Default 2004 MSM with RPM-based P0300 (no misfire felt)

I wanted to pick the beautiful minds here for a moment, regarding a strange issue I'm having in my 2004 MSM.

About 2 months ago, I started getting a P0300 (multiple/random misfire) code seemingly randomly, and without a palpable misfire actually occurring. I started watching when it would occur, and found that it most reliably throws the code the moment I hit 5,000 RPM. Even more curious, it's most likely to occur when I'm not in boost, but still does when boosting occasionally. Any ideas? The car has no other issues besides this one weird code, and runs perfectly fine from idle to redline. Has basic "Little Enchilada" type modifications. Thanks.

-What could cause what seems to be an RPM-dependent random/multiple misfire code?
-What could cause this to happen more commonly while not boosting?

-Plugs are good and gapped fine. (BKR7E @ 0.30")
-Wires are new-ish, and test fine.
-Coilpacks are new-ish and test fine.
-Crank Position Sensor is new and gapped to 0.020".
-Cam Angle Sensor is new.
-MAF has been cleaned.

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Old 09-12-2016, 01:02 AM   #2
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Will be following this. Had the same thing happen to me last time I put my stock ecu back in for smog. Had to keep the revs low so I wouldn't trigger an mil. MS2e all the rest of the time and car runs great.
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Old 09-12-2016, 08:13 AM   #3
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For whatever reason, I'm still thinking it's an issue with the Crank Sensor or Trigger Wheel. Everything looks fine though, including timing marks, condition of teeth on the trigger, and no crank pulley wobble. The fact that reliably, between 4800-5000 RPM a blinking CEL w/ P0300 pops-up, leads me to believe it's something related a sensor that monitors rotation of an engine component. Crank and Cam sensors are new though...

Compression or leak-down hasn't been tested, but I assume I'd notice if I had any valve / valve spring issues that would cause a high RPM misfire (supposedly).
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Old 09-13-2016, 12:28 PM   #4
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Do you have an aftermarket damper? I have an ATI and this happened the first time I put the stock ECU back in for SMOG after I installed the damper. Thought it might have had to do with the aftermarket damper/trigger wheel combo.
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Old 09-13-2016, 01:14 PM   #5
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Nope. All stock. Thanks for your thoughts.
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