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Strange misfire issue

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Strange misfire issue

Postby ali2992 » Fri Jun 19, 2015 8:43 pm

Long story short, I have an mx5 mk1 1998 engine in a kit car, its using a megasquirts ECU which is configured to a default map for the engine running itbs. When I first ran it it sounded a little bit lumpy, and after 3 minutes or so my new stainless exhaust manifold had been stained a purpley brown from the heat, all except the runner for cylinder #2. I borrowed a timing light and the light would occasionally miss a flash every so often when testing that cylinder, all others worked fine. I've replaced ht leads and plugs, no change. If it was a coilpack issue, wouldn't two cylinders be misfiring as doesn't one coilpack do 2 cylinders? A friend wondered if cylinder #2 was actually running normally (the gun is a bit temperamental) and all the other cylinders are out of time and igniting late, resulting in much higher temperatures than expected? (They get really got, really quick, while cylinder 2 runner is cooler than the others, its still hot to the touch)

I suppose my question is, could this be a coilpack issue? Or does it sound more like a timing issue?

Simultaneously, my idle is reading rather high, cold start climbs to approx 1900rpm, and I can't get it down, the itbs are on their lowest idle adjustment and theres no vacuum leaks. Again, my friend wondered if this was the ECU reading engine speed wrong, as it doesn't sound like its turning over that quick. Is it possible that the ECU is counting the wasted sparks too and reading twice as high?

Any help appreciated, sorry for the wall of text!!
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Re: Strange misfire issue

Postby Li5 » Fri Jun 19, 2015 8:56 pm

Sorry I 'm unable to answer your question :sad:

Many of the Mazdamenders are at Blyton helping keep fellow owners on track, They are buried in the dark cave away from their phones. Unfortunately this means answers maybe a bit slow this weekend. I apologise for this, please stick with us, normal service will resume asap :handgestures-thumbup:

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Re: Strange misfire issue

Postby Lazza » Fri Jun 19, 2015 10:44 pm

Still sounds like a coil pack issue to me. Timing is set for all cylinders together so its impossible for it to be different for individual cylinders. If #2 isn't getting as hot as quick that suggests problem with that cylinder. They should all get very hot very quick. While the coil pack is 2 coils each firing 2 plugs, there might be a problem in the pack where it directs the charge to one of the plugs.

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Re: Strange misfire issue

Postby Mazda Mender » Mon Jun 22, 2015 10:54 am

Have you checked for any furring up in the coil pack sockets?
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Re: Strange misfire issue

Postby nedski » Mon Jun 22, 2015 2:22 pm

:text-imwithstupid: Wayne had one only this weekend all green and furry in the coil pack socket.
After that try a basic compression test.
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