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Discussion Starter · #1 · (Edited)
I'm not sure how long this issue has been present on my RB25DET, but I've only recently become aware of it.

For relevance, I'm running a Power FC with a custom map at 300bhp running 99 RON fuel. I have the Hand Commander displaying a bunch of info, including knock level.

I'll try to explain as best I can:

My usual knock readings seem to be fluctuations around 0-10 at idle, occasionally spiking a bit higher. Some fluctuation between 5-20 under hard acceleration, occasionally spiking a little higher up to 30. Regular acceleration usually makes it stay below 15. Often I can go from idle to redline under heavy acceleration and it peaks at 10-20 all the way through the gears, sometimes a little higher. Sometimes I can go out for an hour drive and it never goes above 15, other times it goes slightly above 15 several times in a single short trip.

However, I've recently noticed that cruising along with light throttle maintaining speed in 4th or 5th gear with the revs around 2000rpm results in knock readings constantly between 15-30. If I push the throttle down to accelerate or let off completely, the knock readings disappear. This also only happens under constant load, it doesn't read anything when holding at the same place in neutral or accelerating through 2000rpm. If I change gear to keep the same speed but changing the constant revs lower or higher than ~2000rpm, the knock level stays below 10-15 for the most part.

I've been checking and changing the oil frequently, using only recommended oil and recently did a full oil and filter change 400 miles ago. The car seems to run and drive fine otherwise, and even with the knock sensor bouncing between 20-30, there's no audible or visible indication of any problems unlike the last time I experienced knocking.

I've read the usual stuff about how knock level is different for each car and doesn't always indicate a problem, but this instance seems rather specific to me. I'm hoping it's something like harmonic interference due to an alignment of conditions or something I can change on the map, but I really don't know enough about the situation to say.

Is this something I should be concerned about?
 

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You have kind of answered your own question, the knock sensor which is a piezoelectric device does wear over time which can cause spurious reading and engine wear characteristics can play a part in the harmonics/vibrations from the engine, you could try replacing the sensor and there are also dedicated knock sensors which were known as wideband, like lambdas that were designed to pick up frequencies that were more an indication of actual detonation but not seen any for some years.
 

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Discussion Starter · #3 ·
You have kind of answered your own question, the knock sensor which is a piezoelectric device does wear over time which can cause spurious reading and engine wear characteristics can play a part in the harmonics/vibrations from the engine, you could try replacing the sensor and there are also dedicated knock sensors which were known as wideband, like lambdas that were designed to pick up frequencies that were more an indication of actual detonation but not seen any for some years.
That's good to know, I'll have a look at replacing the sensors when I get a chance.

Out of curiosity, is there any way to reliably differentiate between ambient knock readings and readings being caused by actual problems, or is it just a matter of keeping an eye on things and seeing if anything else indicates issues?
 

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That's good to know, I'll have a look at replacing the sensors when I get a chance.

Out of curiosity, is there any way to reliably differentiate between ambient knock readings and readings being caused by actual problems, or is it just a matter of keeping an eye on things and seeing if anything else indicates issues?
Unfortunately not with the std sensor and the PFC I used to run a dedicated setup for knock on my Supra but don't remember the maker.
 
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