PL, SM and Knock Gauge Question

[Scoobum]

Where does PL, SM and the knock gauge pick up their knock from? Reason I'm asking cuz I use the knock gauge on the pillar to get my foot out of the loud pedal if I see it 'light up'. Last week during one of my two runs I saw the knock gauge come on with 2 green lites. I was gonna get my foot out of it...but they went out. If I had half a brain I woulda hit recall on the SM to check for KR...but didn't. PL log showed no KR...why? Should all 3 of these instruments not show KR? Does the knock sensor not 'hear' the knock...send it to the ECM...and the ECM fires it off to the 3 devices?

[earlbrown]

I'm going by memory here as I did some reasearch a while back to make a freestanding knock detection device' out of GM parts like ours to fit on engines that have no knock data.   (I was inspired after a buddy grenaded his SVT Lighting on the dyno and later when I got a prochager for my BBC jetbaot engine).


The knock sensor talks to the ESC module, and the ESC module is the middleman that talkes to the ECM.

it seems like knock gauges go directly to the knock sensor, so if that's true, it's kinda acting like an ESC module with it's own internal filter circuitry.


And interesting thing I did learn was that most all the GM knock sensors are the same. They're just a piezo microphone that listens to a certain frequency range.

The GM ESC modules on the other hand were different and were based on the engines bore size.


...then I lost interest and went back to looking at pictures of women with no clothes on.

[Steve Wood]

Far as I know, Earl is correct.    What we see on scantools is the fiiltered result after the ecm decides if it is knock, or not.  The knock alarms see the unfiltered input data instead so they often show knock that does not show up on the scantool and it is probably not knock-just a noise the sensor heard.

I did not know about GM sensors in general but I think the GN sensors are filtered to pass to the ecm frequencies around 6000 hz based on bore size.

[Scoobum]

If the ECM decides it's knock...does it cut timing?

[Steve Wood]

I think the factory chip could kill the wastegate solenoid to minimize boost and pull some timing as well.  Far as I know, these functions were deactivated in aftermarket chips because false knock could knock it on its face.   question best asked of Eric

[Scoobum]

As I said in Earls thread, when I overboosted the engine last month the KR went to 14.8...and the timing remained level. I'll do a search tomorrow on the other board...maybe the same question has been put to Eric before. Curious to know what he does in his chip in that regard.

[daveismissing]

http://www.turbobuick.com/threads/unexplained-knock-files-and-pics-attached.442829/#post-3685925

[Steve Wood]

I must be getting old to forget that...lol

Before I went to the slightly shorter belt, one of my cars would allow the pulley to hit

[earlbrown]

Eric explained that one.  Much like when you unplug the MAF the scan tool doesn't' report actual data.   Sometimes you have to learn when not to trust your tools. This looks like another one of those times.



That shorter belt really make a difference.  I came across about 5 Goodyear Gatorbacks a while back and swapped mine out on general principal...
  I need to move those things too. Summit lists them as discontinued and wanted $26 each when they were available!

[aminga]

I think the factory chip could kill the wastegate solenoid to minimize boost and pull some timing as well.  Far as I know, these functions were deactivated in aftermarket chips because false knock could knock it on its face.   question best asked of Eric

I thought on the stock chip the Wastegate was just on a timer. It just commands a duty cycle on the solenoid and then pulls it after an ammount of time that roughly corresponds to second gear.

At any rate the knock gauges are hooked in to b7 on the ECM input this is the raw signal.  There was a good article at one time that I can't find now that discussed how the ECM and ESC module reacts to knock. It was a kind of predictor corrector control system

[Steve Wood]

As I think I said, I am not 100% sure.  We know it would pull timing and I think I read it would pull boost, but, when my car was new, it would pull 14 psi for a couple of seconds or so and then drop back to 12.  I went aftermarket early in the game and that feature was wiped out in lieu of constant boost.

[Forzfed]

Eric explained that one.  Much like when you unplug the MAF the scan tool doesn't' report actual data.   Sometimes you have to learn when not to trust your tools. This looks like another one of those times.

That shorter belt really make a difference.  I came across about 5 Goodyear Gatorbacks a while back and swapped mine out on general principal...
  I need to move those things too. Summit lists them as discontinued and wanted $26 each when they were available!

Looks like your a red hair away from the bracket.

[Scoobum]

I read a post from Patrick Rubio years ago about possibly running into boost issues using the solenoid past the stock boost level. I've run mine tuner style ever since.

[earlbrown]

That shorter belt really make a difference.  I came across about 5 Goodyear Gatorbacks a while back and swapped mine out on general principal...
  I need to move those things too. Summit lists them as discontinued and wanted $26 each when they were available!

Looks like your a red hair away from the bracket.

It looks a little closer in the picture than in real life. Once I ran the car for about a minute and the belt found it's happy place, it moved away a little.

[Forzfed]

So we are talking a black curly hair?