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Knock Detection

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Hi everyone,

Question for the group regarding knock. Currently tuning an RB26 with dual knock sensors on the Elite 2500 with ESP. Sensor 1 shows a consistent 10-20 dB higher than Sensor 2. I understand that both sensors are picking up the frequency of the harmonics independent from each other. My questions is, should these sensor mirror each other? What is an acceptable tolerance window between the two? Most important which input should be used to set the knock threshold. My concer is setting treashold off the higher knock 1 signal and not picking up real knock on the knock 2 sensor behing that treashold will be set too high. Is 10dB diference too much deviation between them?

I'm unsure that ESP provides the capability to set dual bank knock threshold limits and individual knock trim corrections. I know an audible knock control strategy needs to be utilized in order to correctly set threshold. Just unsure if the ESP software allows to set limits or additional generic tables will have to be created. I would like to set an RPM/Map/Throttle table of when to correct Long Term Knock trim and when to ignore it, just in case, in the event that a bad tank of fuel is the culprit.

Any advice from experinced with this issue will be greatly appreciated. Thank you.

Jose G.

hello are you seeing the difference all rpm and load of just one area ?

Hi Jose, that's a little unusual and normally I'd expect the levels to be relatively closely matched. There's no way to trim the gains individually between the two sensors so there's no easy solution here. If you're running the original sensors then it may be a problem with one of the sensors that's causing it. The RB26 just uses a standard bosch donut style knock sensor which are cheap and easy to source. As a test you could swap the front and rear sensors location and see if the level imbalance moves from one sensor to the other.

In terms of dealing with this=, you really have no option but to use the threshold from the higher sensor output, otherwise you'll be falsely triggering the knock retard. You normally find however that the difference between normal background noise and knock is quite significant so it may not actually be as critical as you think. Also, while two sensors on an inline 6 is ideal, you can still get away with a single sensor on these engines so this isn't necessarily the end of the world.

I thought it was a bit unusual myself. Im seeing the difference in all RMP and load. We already swapped 1 and 2 knock sensor positions and the signal diviation did Not follow. We also swapped out the sensors with spare RB26 sensors (not new) and we saw no change in signal.

I did set the knock treashold to the higher knock 1 output, however im waiting for the Plex knock monitor system to arrive in order to properly add timing.

Thanks for the feedback.