Knock sensor processing

[tvrgeek]

Just about to order a MicroSquirt and do an ignition system on one of my MGBs. I am testing a Bosch knock sensor and I should be able to do the bandpass filtering. My goal is to see what I can wring out of it with the Weber DGV still there. ( EFI is stage two) This is a street car.
Assuming I can get a reliable signal, which may be a stretch on this old lump, I have lots of questions on the software as it pertains to knock sensors.
*Does it do the time windowing? I only want to look for knock a few ms after ignition.
*If I run it into one of the ADC lines, is the software already set up for the threshold detection?
*Is there any DSP capability on the ADC inputs to implement bandpass. ( I want to see 7K above a threshold for 5 cycles kind of processing)
*If I did the threshold detection in the external filter, is there a digital input or should I just use the ADC input.
*When you detect knock, you want to back off the timing a couple degrees across some mid-RPM high load area of the maps. Any ideas on this?
*When do you let it back in? Next power cycle, when the MAP goes back up? Do I just take it out and put it back one degree at a time a sew seconds later?
* Do I make the map as close as I can and just let the sensor trim under unusual situations, or do I set the map very aggressive and rely in the sense to pull it back constantly? The age old servo question, stable and trim or unstable and control.

Is there a great big FAQ somewhere that answers these and the issues I have not thought of yet? I have not found one but there are a lot of forums dedicated to the MS. I could have missed one or two.

[Matt Cramer]

First, note that the MS3 and MS2/Extra have separate support at MSExtra.com. This forum is specifically for the B&G code.

Does it do the time windowing? I only want to look for knock a few ms after ignition.

MS2, no.

MS3, yes.

If I run it into one of the ADC lines, is the software already set up for the threshold detection?

MS2/Extra and MS3 have a threshold voltage setting; I am not sure if the B&G code does not.

Is there any DSP capability on the ADC inputs to implement bandpass.

MS3 supports an add on DSP based module; MS2 does not.

When do you let it back in? Next power cycle, when the MAP goes back up? Do I just take it out and put it back one degree at a time a sew seconds later?

You can do either one - pull timing as long as you're in that cell, or let it back in based on time.

Do I make the map as close as I can and just let the sensor trim under unusual situations, or do I set the map very aggressive and rely in the sense to pull it back constantly? The age old servo question, stable and trim or unstable and control.

The timing that makes best power is often well before the knock threshold, unless your engine has odd hot spot issues or the compression is too high for pump gas. If the engine is knock limited, running an aggressive timing map and having it pull knock all the time is only a good idea if the engine is fairly detonation resistant. Some Subarus run this strategy - apparently the turbo setup on a boxer layout produces heat issues that make these engines very knock prone.

[tvrgeek]

Much thanks. Looking at either the MS-II or micro. Not "extra" or 3. There are so many derivatives of the forums, I'm not sure where to go.
This helps quite a bit with my planning.

So, I don't really want to run only a couple degrees behind knock? More bad advice previously. While I still have a carb, my AFR will not be as well controlled as optimum, so trying to put the sensor in closed loop still makes sense even if the advance is not as aggressive. Looks like I need to do most of the work in my external analog piece. At least I am pretty good with analog.