What gives knock sensors

[Bartly]

So
I am hoping this is sorta a thing others see with going WOT. I’ve been adding a cup of race gas concentrate (similar to Torco) and it does a good job turning my 91 octane gas into what I’m thinking is 93-94 octane. I have max timing at WOT at around 17 if that matters.
So if I start easing into WOT around 3500-4000 rpm I get -1-2 (negative) KR values and I am happy. But if I stomp on the gas pedal and go WOT at the same rpms the KR values get up to positive 3-4. This is with the same tank of gas (and various tanks for quite a while now). Curious what the consensus is on this, is this just the way the sensors react to hitting WOT hard, or is it something that should/can be adjusted out with the tune? Car runs great, just something I’ve been meaning to ask to see if others notice the same thing.

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[Jay-rod427]

I've heard of it before if you just stomp it like you are describing. Does it quickly fall off back into negative, or stay positive until you let out? Lund had to desensitize mine slighty as there was about a 80% chance it would show positive knock horribly( basically impossible on E85) and stay at like 8 degrees timing until I let out of it. Runs great now and still adds timing as it should when they are happy.

 

[Bartly]

I've heard of it before if you just stomp it like you are describing. Does it quickly fall off back into negative, or stay positive until you let out? Lund had to desensitize mine slighty as there was about a 80% chance it would show positive knock horribly( basically impossible on E85) and stay at like 8 degrees timing until I let out of it. Runs great now and still adds timing as it should when they are happy.

It stays that way throughout the pull. If I enter softly and go WOT KR will stay negative through the pull. If I hit the gas hard it will go positive and stay there until I let off.
It’s weird because it doesn’t always act this way, most the time it’s negative but on some pulls it goes positive and the only thing I’ve narrowed it down to is how fast and hard I get into WOT.

 

[Jay-rod427]

Exactly what mine would do. Once they're pissed they would stay that way. Lund Jr said it was quite common to desensitize centri cars slightly.

 

[Tommy V]

Also turn your advance trac and do a log,sometimes if you pic up wheel spin it will pull timing and not.come back.in or come back real slow.

 

[Bartly]

Also turn your advance trac and do a log,sometimes if you pic up wheel spin it will pull timing and not.come back.in or come back real slow.

Not sure what you were going with? Turn it on or turn it off?

Are the knock sensors affected by wheel spin? I would have only thought they pick up noises in the engine.

I could see wheel spin somehow dictating to the cars computer to reduce timing, but I wouldn’t have though they would have made it so the knock sensors change values when wheel spin is detected?

 

[t14mhall]

So
I am hoping this is sorta a thing others see with going WOT. I’ve been adding a cup of race gas concentrate (similar to Torco) and it does a good job turning my 91 octane gas into what I’m thinking is 93-94 octane. I have max timing at WOT at around 17 if that matters.
So if I start easing into WOT around 3500-4000 rpm I get -1-2 (negative) KR values and I am happy. But if I stomp on the gas pedal and go WOT at the same rpms the KR values get up to positive 3-4. This is with the same tank of gas (and various tanks for quite a while now). Curious what the consensus is on this, is this just the way the sensors react to hitting WOT hard, or is it something that should/can be adjusted out with the tune? Car runs great, just something I’ve been meaning to ask to see if others notice the same thing.

I just noticed this myself earlier today and was going to post about it LOL. I've done plenty of WOT logs and there is no knock, so I guess this is just what happens when you mash the throttle at a lower RPM.

 

[ahl395]

Probably false knock. Check around the car for the many (many) causes of false knock or you can ask your tuner to desensitize.

 

[JPSTANG]

Your most diffidently are not alone, mine is even weirder... only does it in 4th gear, mash it knock up to 6 to 8, hard shift from 3rd same thing, but just ease into it and nothing. any other gear hard from 2nd to 3rd neg knock all the way up. figure that one out and ill give ya a cookie... lol

 

[Tommy V]

Not sure what you were going with? Turn it on or turn it off?

Are the knock sensors affected by wheel spin? I would have only thought they pick up noises in the engine.

I could see wheel spin somehow dictating to the cars computer to reduce timing, but I wouldn’t have though they would have made it so the knock sensors change values when wheel spin is detected?

Turn it off,i have seen hundreds of logs and wheel spin depending on how much will cause the knock sensors to pull timing.Do a log with advance trac off.Also if you are saying you ars dojng a 3rd or 4th gear pull and have in sport mode where the car dont downshift,depending on how low of a rpm that you start the pull at you will get burst knock.All these car do it and most tuners dont know why but say its normal.Evertime i have done a log and let the car downshift on its own and had advance trac off i get no knock.

 

[Jay-rod427]

Just like everyone responded so far it's centri cars, and Lund jr said the same thing. My personal theory is it's blower gearbox noise, and the belt buzzing. Since they're hard bolted to the motor it gets picked up because the knock sensors are so damn sensitive.

 

[Tommy V]

Just like everyone responded so far it's centri cars, and Lund jr said the same thing. My personal theory is it's blower gearbox noise, and the belt buzzing. Since they're hard bolted to the motor it gets picked up because the knock sensors are so damn sensitive.

I have not seen a tune yet but the whipple cal that has not had the knock.sensors desenstized on blower cars.And i have see alot of tunes!!

 

[Bartly]

Turn it off,i have seen hundreds of logs and wheel spin depending on how much will cause the knock sensors to pull timing.Do a log with advance trac off.Also if you are saying you ars dojng a 3rd or 4th gear pull and have in sport mode where the car dont downshift,depending on how low of a rpm that you start the pull at you will get burst knock.All these car do it and most tuners dont know why but say its normal.Evertime i have done a log and let the car downshift on its own and had advance trac off i get no knock.

Thanks for the info. My car is a manual and I mostly only pay attention to 3rd gear as that the gear I get to play with (no race track around for me). I try to wait until 4K for WOT, but sometimes lower. And yep I’ve noticed it just top of at a +KR value and ride it till redline, thinking that’s the burst knock you are describing. Yeah I’ll have to try with turning it off and see what the KR looks like. Hate to admit it, but I never turn it off and I’m sure it’s saved my car more than once, lol. But will be interesting.

I am happy that it’s a phenomenon that seems fairly common, I half figured it was, but had to ask. It seems like most mention (or omit to mention) they don’t get any +KR readings when talking about their setups, and I wanted to see if this situation was happening to others. Makes me feel better.

 

[Bartly]

Probably false knock. Check around the car for the many (many) causes of false knock or you can ask your tuner to desensitize.

Yeah, I’ve lost count who’s many times I’ve crawled around my car/engine looking for anything rubbing on the engine or any hard parts mounted to the block. Seems if something was rubbing or vibrating it would occur just as much whether I stabbed the gas peddle or eased into WOT. But, I can see an impulse triggering it so maybe stabbing the gas peddle would make it show up?

 

[Bartly]

Your most diffidently are not alone, mine is even weirder... only does it in 4th gear, mash it knock up to 6 to 8, hard shift from 3rd same thing, but just ease into it and nothing. any other gear hard from 2nd to 3rd neg knock all the way up. figure that one out and ill give ya a cookie... lol

That does sound very similar to what I have going on, but I see it in 3rd gear. Go ahead and eat that cookie, I don’t think I’ll earn it, lol.

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