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Crank sensor - look down
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Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Wed, 30 Jun 2004 06:11:33 Share Post by Email
In Reply to: Good article & diagnostic questions, JohnCC, Wed, 30 Jun 2004 04:09:37
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Anders posted a nice scope picture of a crank sensor output just a few posts ago-

http://www.saabnet.com/tsn/bb/9000/index.html?bID=181708

As the enclosed article notes, the knock signal is on pin 7. It states that it outputs 50-100 mv (AC) at idle, and that 300 indicates large amounts of knock.

I imagine that putting a good high-impedance scope probe on pin 7 would shed some light. What was clear from the article was that 300mv was a large amount of knock. What wasn't clear is if 50-100mv means knock or not. Since knock at idle is pretty rare, I'd guess 100 mv is no knock; but that's just a guess.

The ionization of the combustion charge varies with the onset of knock, and with true knock. I think that with ionization detection (which is what the Trionic DI does), it can actually determine conditions for the onset of knock.

Since the DI/APC's job is to prevent knock, I would imagine that in a properly functioning engine, you won't see a knock signal - the system will be adjusting timing/fuel/boost to prevent knock. So if you're interested in seeing how close to knocking you are, you'd need to see the changes in timing. If you really see knock, then the DI/APC system isn't controlling knock, probably due to a fault somewhere. And determining the location of a fault in a closed loop system is tricky. And when there are multiple control loops, it gets event trickier.

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