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Misfire at high rpm

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Old 10-10-2018, 08:09 AM
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Misfire at high rpm

I'm getting some misfire at around 8-9k and then a lot past 9k. you can see a little dip on power at around 8700, some misfire there, then after 9k, a lot of misfire. i let off before before hitting rev limit at 9300 because of so much misfire. the check engine light is not blinking from misfire (which it has before at lower rpm during cruising, but went away when i replaced MAF sensor).

New ported engine
AC Delco D585
Bennett Built LS coil harness and MSD 8.5mm plug wire.
Versatuner

Last edited by trackjunkie; 10-10-2018 at 08:13 AM.
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Old 10-10-2018, 08:17 AM
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Just thoughts that you may have already addressed but didn't mention...

Have you tested the coils with an HEI tester? The D585s are supposed to be more robust but that doesn't eliminate the possibility of one or more going bad.
Also, have you altered the coil dwell settings? All else being equal, D585 coils need a longer dwell than OEM.
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Old 10-10-2018, 08:38 AM
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all components are new. did not test coils with HEI tester. did not change dwell settings. wasn't sure what these numbers represent in the dwell table.


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Old 10-10-2018, 11:04 AM
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This thread has good info. It also has tons of the usual petty bickering and stuff.
https://www.rx8club.com/series-i-eng...ssport-178635/

This post specifically relates how to convert from the dwell table to human-usable numbers:
https://www.rx8club.com/series-i-eng...5/#post4260808

Here's TeamRX8's big contribution with his usual flair...
https://www.rx8club.com/series-i-eng...5/#post4311570

I'm not saying this will definitely solve your problem but it's a potential issue.
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Old 10-10-2018, 11:15 AM
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thanks for the info, i'll dig through them.
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Old 10-10-2018, 11:25 AM
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Originally Posted by trackjunkie View Post
thanks for the info, i'll dig through them.
No prob. I'm using the values from TeamRX8's post with D585 coils and haven't had any problems at high RPM during track/AX use.

That said, if you think that's a good reason to copy my work copying his work, I have some elephant repellant to sell you.
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Old 11-02-2018, 09:33 AM
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Did you fix? i still get occasional, intermittent power loss, stumbles, surges... i am thinking ESS, MAP/Baro sensor, or the ignition condenser. my coils, wires, plugs, MAF all new, injectors flow tested, new fuel pump, pulls great... most of the time! dang intermittent issues...
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Old 11-02-2018, 10:18 AM
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i dont get misfire/CEL anymore while driving on street after replacing the MAF sensor, but did get a big stumble, feels like a complete engine shut down for like a split second. that used to happen more often before replacing the MAF, even when on track. After replacing the MAF, it only happened once on street.

on track, i was still getting CEL blink during light throttle at the last track event.

since switching to e85, i didnt get misfire near redline like i did before on 93 pump gas while on the dyno. so i'm hoping there wont be misfire on track at the next event. when it misfire on the dyno before, i can hear it but no CEL blinking.

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