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Murg31 Murg31 is offline
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Car: E91 335xi
Default Relation between Spark Plugs, Ignition Coils and Timing Drops - 10-05-2021, 04:17 AM

Hi all,

I recently found a discussion about the N54 ignition system in a German forum, where the consensus seemed to be as follows:
  • Old coils discharge later than fresh ones. Hence combustion happens later.
  • Switching to fresh coils can lead to pre-ignition, because the DME (or the tune) adapted to weak coils. The fresh ones ignite the air-fuel-mixture earlier and therefore the DME is more likely to pull timing.
  • Spark Plugs with an adjusted gap have a lower chance of having the spark blown out at higher boost, however the spark itself is smaller and therefore the air-fuel-mixture takes longer to fully ignite. This has the same effect as lower ignition advance

So the derived relations were like this:
  • New Coils: reduce misfires, but dont help with timing drops and possibly make them worse
  • New Plugs (gapped): help with misfires and timing drops, but reduce idle smoothness and max. power (due to the same effect as lower ignition advance)

Would you agree with these statements?
I am wondering because I am having more timing corrections with new coils and plugs (Eldor + NGK 95770 @ 0.022") than I had before with the same boundary conditions. Logs can be seen here: https://www.n54tech.com/forums/showthread.php?t=66571

I am unsure about the point with new coils and timing pulls due to pre-ignition. This would mean that the DME has adaptations for old coils, is this the case?

Best regards from Bavaria
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bekloptupus bekloptupus is offline
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Default 10-05-2021, 10:43 AM

I doubt it – I’m just guessing, but if new vs. old coils really did introduce a significant reduction in lag that could not be compensated for by the anti-knock dynamic timing, then there would have to be an ‚anlernen‘ feature to cope with exactly the scenario put forward.
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