I posted this question yesterday, but it disappeared. I see that it is a seemingly solid donut-shaped piece of metal with a bolt going through it's center holding it solidly against the engine block. How can this transmit a signal to retard ignition timing, and also, how not mistake other noises or vibes for pinging or knock? -Jeffy. p.s. I posted this here because only people interested in mods are going to know or care about this question.

 

http://www.autoshop101.com/forms/h38.pdf
http://www.siemensvdo.fr/NR/rdonlyre...atasheeten.pdf

 

Piezoelectric crystals translate motion in to electricity, or visa versa. Inside your earbud headphones is a small crystal that has the electricity from your iPod going to it-the electricity causes the crystal to vibrate, making sound from the motion.

You can reverse it, and tune the crystal to vibrate at a certain frequency. So you get an electrical signal out of the crystal when it vibrates due to the knock. A knock is kinda like rapping the block with a hammer-it's a big bang. The frequency of the knock is a known frequency, so the crystal gets tuned to it. That's the reason it doesn't go off due to other noises or vibrations.

 

Thanks for that info- I really wasn't expecting an exacting answer right away, but I sure appreciate your time! People like yourself make this forum worth-while. Some people know the answer to your question and take the time to school you. That was good stuff- Thanks! -Jeffy.

 

No problem. I know a little more now too!

 

So how can I monitor knock using the stock sensor?

 

To monitor knock you need to tap into the voltage signal either through the computer or with a direct link... other's can probably tell you which is most feasible.

 

It should also be noted that the sensor is tuned to the knock frequency of a specific engine design as engine block designs will have different resonating characteristics, so while they may look the same they are not necessarily interchangable. Always check part numbers. Note how the relation between frenquencies is shown in the diagrams, but not the actual Hz data.

A very good book about EFI principles (including knock-sensor operation):

http://www.bentleypublishers.com/pro...FIB&subject=25

While the specific systems covered are a bit outdated (and sadly, Charles Probst has passed on...), the principles have not changes and are described in basic terms very well. This book should be mandatory reading for any budding modern-car DIY'er.

 

Mmh, I see. Thanks for the reply, so if I wanted to make an analog connection to a device with a 0-5v analog imput how should I do it?

 

Honestly, I'm not sure... and personally, I wouldn't tap into the wiring as it could change the data the ECU sees. I believe some of the better OBD II monitoring programs can output knock sensor data. Besides, I'm not really sure what you're going to see in real time. The ECU is constantly adjusting the timing to keep the engine on the ragged edge of knocking... and as such knock is sensed and compensated for in fractions of a second.

 

Well, if there is a condition the ECU can't adjust to and it causes knock, you should be able to see it in real time...

 

Well, maybe... but if that happens, the ECU will likely throw a code, although I'll admit not always. However, this usually happens with modified S cars, not on NA Coopers. I'm not sure what you could be doing that would cause this in a Cooper, other than wanting to run really cheap gas which in general is often robbing Peter (engine efficiency & MPG) to pay Paul (cheaper fill up costs)...

By design, the transducer doesn't produce much current. I wouldn't do anything that could possibly steal some of that current. Like I said before, I would look for a program/device that pulls data from the OBD port.

But that's just my admittedly conservative opinion and I'll leave it at that.

 

Ah, well, it's a valuable opinion. To tell the truth I was thinking about going with a big valve head and cams, and while this shouldn't cause the engine to knock with a proper tune afterwards, if I found a way to monitor it, it wouldn't be too bad I think

 

i believe that many of the devices on the mini, related to the ECU, use the CAN BUS, and all are sensitive

from Bentley 600-2 -- use digital multimeter only, an analog (swing needle) type may draw enough current to damage components

from Bentley ELE-66 (component B6240) -- plugs directly into the A6000 (DME) computer at PIN locations 7, 8

no info that I can parse on voltage, or signal type (but I rot at schematics)

 

Wow, my SES came today and I pulled a code P0326. What do you know, a Knock Sensor thread.
Make: MINI Model: Cooper Year: 2005
VIN: Not Reported MIL: Off
Diagnostic Trouble Codes P0326 Knock Sensor 1 Circuit Range/Performance (Bank 1 or Single Sensor)

]Freeze Frame (Frame 0) for DTC P0326
Absolute Throttle Position: 21 %
Calculated Load: 48 %
Coolant Temperature: 190 F
Engine RPM: 2426 r/min
Fuel System Status Bank One: Closed Loop
]Fuel System Status Bank Two: Not Reported
Ignition Timing Advance for #1: 20.0 deg
Intake Air Temperature: 99 F
Intake Manifold Absolute Pressure: 15.9 in.hg
Long Term Fuel Trim Bank One: -0.78 %
Short Term Fuel Trim Bank One: -6.24 %
Vehicle Speed: 48 MPH

Any ideas about my problem - bad sensor or bad gas?
TD