Knock Control Explained

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Haltech Staff
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Joined: Mon Jul 07, 2008 12:24 pm

Knock Control Explained

Postby HaltechAdam » Tue Jan 12, 2010 3:18 pm

rcdash wrote:Can one of the Haltech engineers please define "Knock Level Display" vs "Knock Level Logged"?

Knock Level Display is the channel that you should use when displaying on ECU Manager gauges. You also use this with the laptop logging.

Knock Level Logged is the channel that you use when you are logging knock with the on-board datalogging.

The reason we need these separately is because knock is a fleeting event that lasts only briefly, so to ensure that the ECU Manager or the datalogging sees these events, there are separate channels that hold the highest value until the value it conveyed to the ECU Manager or data logger.

rcdash wrote:Also how do the Knock threshold values (expressed as a percentage) relate to the raw knock value in mV vs. the above two parameters (expressed as raw values)? There is a brief description of tuning for knock detection, but it seems to be very difficult to practically achieve accurate knock threshold values for each cell because of:

1. the difference in units of measure between the various parameters and a lack of understanding of how they relate (the knock detection algorithm is a mystery)


2. the inability to localize a knock event to a specific cell in the knock threshold table in real time street tuning (or is this indeed possible?)

The Knock Level Raw is intended only to use as a diagnostic channel to indicate if your knock input on the ECU is receiving a signal.

The relationship between knock signal in mV and the knock threshold table is quite complicated and not practical to use for tuning.

The best way is to calibrate the knock threshold table is to calibrate it against the processed signal, which would be the Knock Level Display channel. You do not need to localize the knock since the calibration is done when the engine is not knocking. The idea is to set the thresholds against normal engine noise. Typically this is done with ignition timing reduced to ensure that no knock is present.

Using a dyno is highly recommended as you can gently apply varying amounts of throttle and listen carefully for knock. Using knock listening equipment is also highly recommended since you will often pickup the trace knock sounds prior to the audible knock that you can hear without such equipment.

This is an advanced feature and used for engine protection, so its recommended that the best tuning method and equipment be used. You can street tune this table, but the tune may not be as precise, and may take a lot of hours before you arrive at a tune that you're satisfied with. Consider how much effort GM, Ford, Honda, Toyota etc. would invest in this area :!:

However, when knock is present, the Knock Level Display value is typically dramatically higher than the background engine noise, so setting thresholds slightly higher to prevent false positives will often not mask out the knock. Always use a lot of caution when testing with real knock and any real knock testing is optional and done at your own risk. Knock at high cylinder pressures (when the engine is making a lot of torque) are to be avoided.

The summary is that with the signal processing, we've masked much of the background noise to make tuning as easy as possible, but you still need to be careful when calibrating the Knock Threshold table to ensure you get reliable knock detection.

We're in the process of improving the knock section in our help. I hope the above explanations provides the necessary information in the meantime.

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