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Driveline, Engine & DME Tuning
Talk about driveline improvements, NA tuning and DME tuning your E46 BMW here. This includes diffs, intakes, exhausts, chips, software and OBD tuning.

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Old 07-09-2019, 05:37 AM   #1
Blu302
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My Ride: '98 E46 323i
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MS43/42 DME hardware

Has anyone had the time to disect the DME hardware on MS42/43 DME's?

I am specifically asking in regards to the knock sensor conditioning circuit.
I can't find my old DME's I have opened up and was hoping that someone else had some insight into "inner workings" of these things.

I know that they run piezo knock sensors which makes it near impossible to just measure the sensor to get it's parameters.

I am doing this so I can re-purpose my spare sensors for other projects and use my current fitted(disconnected) sensors on my modified engine.

Any ideas/help appreciated.
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Old 08-05-2019, 07:36 PM   #2
Blu302
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For anyone interested,

It uses a differential signal into a knock IC.
It has a series of 2KΩ resistors mirrored on each "leg" of the sensor with a basic filter. The sensor has a bias voltage applied to the signal output end of the string.
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Old 08-06-2019, 04:11 AM   #3
SiBriers
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Interesting - are you thinking that the filter components could be changed / tuned to allow a bit more knock then?
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Old 08-06-2019, 07:36 AM   #4
Blu302
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My Ride: '98 E46 323i
Year: 98
Model: E46
Transmission: Manual
I am running the sensors into a custom knock IC as the factory DME is long gone. The readings I have measured are noisy and random. I am going to put it through an FFT and pull the frequencies related to knock.

The factory system is broad band and integrates the total signal to get the overall level of knock. The factory system is not "tuned" enough to allow for easily running at the knock limit and not having timing pulled randomly.
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