Bengt Sweden

I would like to have a warning light connected to my knock control system. The codes that you get from the diagnose outlet is not very useful.
Does anyone have an idea?

Bengt

rcldesign

make a full wave rectifier with an infinite impedence input, low pass filtered to smooth the output voltage, and hook it up to an LM3914. You will need 2 OpAmps, the LM3914, some LEDs (4-10), a few discretes, a few diodes, and you're set. You can use the input buffer to adjust the gain on the signal with a pot. This is a pretty sucky way to do it, but it works, and this is how most knock meters work. The reason this isn't too cool is that as RPM increase, so does ambient engine noise, and these detectors will register that noise as some amount of knock. Then you get to play with the amout of gain in the system to get a useful measurement, and so on and so forth.

An alternative is to make the infinate impedence imput not go to a filter, but to an a/d converter which samples it for a DSP which runs an FFT (slow) or DFT (faster) on the samples, looks for particular frequency (which is motor dependant) spike, and its harmonics, then calculates the power spectral density of the knock signal, compares it to the other 'noise', and then essentially calculates a signal to noise ratio that can be interprited as the amount of knock. This works better because it takes in to account the other engine noise, and makes its "how much knock" answer based on its relation to noise. As such, once you know what frequencies to look for, it never has to be calibrated or adjusted, and it will give accurate measurements over all rpm. In fact, I have an algorithm to find the knock frequencies, but I never got around to putting it on a DSP and making a car knock to test it <img border="0" title="" alt="[Wink]" src="wink.gif" />

Or for the novice, you can pick up a knock meter for pretty cheap (though you'll probably only find one like the first one described).

Bengt Sweden

Ok, thanks. I guess this is a way to improve the sensitivity while being able to filter out noise better than the stock system. I have heard of people feeling knock control activate on curbs or by stone spray in the fenders.
I have also been told about systems with double sensors to be able to sort out noise coming from elsewhere than the engine.
At the moment I am more looking for to get an indication if the stock system activates or not. I don,t want to build a signal decoder if there is a simpler way.

Bengt

rcldesign

Oh, if you want to know the stock system is working, start the car, then tap on the engine block... the motor should stumble if I recall.

m42racer

Start the car, tap on the engine block .....

Ok, now let see if I get this.

Open hood, start the car, select first gear, close the door, open the window. Now let out clutch slowly, climb thro open window while steering car with foot. Lean over fendor, thro open hood and reach into engine bay and tap on block. Once I have mastered this operation, I then use other foot to change gear and accelerate into boost RPM's. Keep tapping right?

Is this what you mean?

fortysixandtwo

Sounds like a two person job. Have someone cling to the front of the car, tapping near the sensor at various rpm's. While you drive along looking through the gap between the raised hood and the rest of the car. Sound simple to me!

Or you could just leave the car out of gear and check for the knock sensors functionality in the driveway, with the car idling. But what fun would that be.

Danno

No no no... the knock-control in the KLR only works when you're under load. I actually suspect only when you're under FULL load at WOT when the WOT/full-throttle maps are used. Those of you with APE chips may have noticed that if you gently roll on the throttle, you'll get a second or two of knocking and pinging on the way to full-throttle? But if you smash the pedal quickly, you can bypass that knocking & pinging completely?

SO you gotta test the knock-sensor while driving the car. Since you're under full-throttle, you gotta pay attention and drive the car straight. Have an assistant, hopefully someone light and small like a sorority chic draped over the engine, facing forward. And the actual ignition retard can't be felt that easily under full-throttle because there's so much acceleration and commotion going on, so you have to measure the actual ignition-timing itself.

Have your assitant aim a dial-back-to-zero timing tight at the hole in the distributor and zero the indicator. Then floor the car and the assitant wil have to continually dial back the timing-light to keep pace with the ignition-advance map. When knock occurs, she'll see the timing-mark on the cam-gear leap backwards suddenly by 5-6 degrees.

Porsche and Bosch did a decent job with the knock-sensing system in these cars, so you might as well use it. The knock-sensor itself is sensitive in the frequency ranges of the particular engine. And the filtering circuitry in the KLR is specifically tuned to knock noises from this engine.

m42racer

Ok, I got it. Get chic to lean over fender will holding timing light with my foot flat to the floor. When she yells back that the timing jumps backwards 5-6 degrees, I slam on the brakes to suddenly slow down the engine to advance the timing again.

Does this new huntley knock control metering device come with the required tie down straps?
Has this device been put thro the typical huntley exhaustive R&D/testing program? (hijack someone elses part, afix huntely decal, make sure its straight, heat cycle the part to make sure decal will not lift off part). I need to know this ASAP.

rcldesign

Huntley knock control metering device? Where did that come from?

johne

Man you guys are too funny.
I think rcl was actually trying to give some valid advice, but still that was serously funny.

rcldesign

Seriously...

Need I remind the court that I am not a Huntley employee? My bad for reading some white papers that a couple of PhDs wrote. Perhaps in the future I should just point people towards products that are already available with no insight to how they work, their theory of operation, what alternatives there are, etc.?

As for the tapping on the engine with the motor running, I could have sworn that I read someone saying that a while ago, but I could be wrong.

rcldesign

To clarify my own understanding of the stock system, I refer some questions to Danno...

Danno,

are the stock knock sensors 'tuned' to particular frequencies, or is this done in the KLR? (there are pretty much two ways to go here, tune the sensor to the engine's knock harmonics, or band pass filter at the KLR side to these harmonics, then perform a power measurement.) I *thought* that the stock sensors were not tuned (i.e. wideband) and that the KLR did the filtering. Do you have information as to believe otherwise?

Danno

Knock sensors are mechanical transducers, microphones that translate mechnical noise into an electrical signal. They are tuned to specific frequencies just like audio microphones. This is done through the clamping materials and its physical dimensions. You'll notice that the steel sleeve of the knock-sensor is a certain material with a certain thickness. This is the first part of the filtering process. The early 951 knock-sensors didn't have the same sleeve and it was changed later for improved sensitivity. Other knock sensors use a brass sleeve of a different thickness to transmit a different range of frequencies. There are "wideband" type of knock-sensors, but they end up with a low signal-to-noise ratio across the board.

toddk911

I just want to tie in an LED to the stock knock sensor so I know when any knock is there, as stated above on WOT it is hard to hear and to notice and timing being pulled back.

Has anyone done this???

AlexE

I would like to do this as well...............