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VTEC phantom knock, how to best config knock floor?

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Car: S2000

ECU: AEM Infinity

Knock Sensor: OEM resonant style

VTEC switchover (sometimes) triggers a loud click/knock event (weird that not every time) that I can see and hear with audio detection. Seems to be intermittent, but because of how I configured knock protection it triggers my CEL and adds fuel, it's annoying.

How did you tune your standalone ECU's knock protection around that pesky VTEC high-lobe engagement (false) knock event? Wait... could it be real since it's intermittent... as it only seems to occur 50% of the time. The knock occurrence shifts/moves with VTEC engagement, so there's a correlation and it is cam-switchover related.

Image attached. Thanks!

Attached Files

It's very unlikely that it's real knock and you can absolutely expect a strong mechanical noise at the VTEC changeover point since the rockers are locking at that point. It is a little unusual that you're reporting it as intermittent though. You could always trim 3-4 deg out of that area and see if that permanently resolves the issue, in which case it would suggest it is knock. You will be able to hear the VTEC changeover with audio knock detection and it will be quite distinct from actual knock since it's one single sharp noise event. This can trigger knock protection in some instances, however if you have the frequency of knock correctly dialled in then this shouldn't be an issue. But otherwise you can fudge things by raising the noise threshold at the VTEC point.

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