Detonation at StartUp

[Wildone]

I have the Caspers knock sensor, and I am wondering how sensitve they are. I have been noticing that I have detonation at startup and was wondering if this is normal. I have set the car
up to run about 16lbs of boost in street trim with a stock turbo and intercooler (have Dutweiller neck). I have to run at a minimum 10 gallons of 110 race gas per fill up to keep the guage from showing detonation. Would the fact I am running synthetic motor oil having anything to do with it. I have also notice a rocker arm that has been ticking, and was wondering if this could cause the knock sensor to go off. Thanks in advance.

John Wilde

 

[TURBOV6]

Probally something lose durring start-ups. Loose exaust or downpipe or maybe your convertor nuts are loose?

 

[Steve Wood]

it is reporting the sound made by the starter when it engages and operates..it's not detonation. They all do it...

 

[turboaddict2]

I thought knock at startup was normal. I always get it up to the yellow before the engine fires up.

 

[azgn]

normal....I sometimes get red on startup

 

[Quick6]

Originally posted by Wildone
I have the Caspers knock sensor, and I am wondering how sensitve they are. I have been noticing that I have detonation at startup and was wondering if this is normal. I have set the car
up to run about 16lbs of boost in street trim with a stock turbo and intercooler (have Dutweiller neck). I have to run at a minimum 10 gallons of 110 race gas per fill up to keep the guage from showing detonation. Would the fact I am running synthetic motor oil having anything to do with it. I have also notice a rocker arm that has been ticking, and was wondering if this could cause the knock sensor to go off. Thanks in advance.

John Wilde

Are you saying that you have to run 110 octane with this setup to eliminate knock at 16psi of boost???????? If so you have other problems like fueling or an engine management problem.

 

[arista5]

it is a normal thing, when i turn on mine, it's usually 2nd green, there isnt a problem

 

[azgn]

lots of noise generated when cranking....not really detonation, but you know if your gauge is working!

 

[gnjones231]

Just another one of those myths about the starter hitting the flywheel and causing knock. It's the knock gauge itself. The reason everyone has this problem is because everyone has the same knock gauge! Noone here has actually looked at the signals to verify that the knock sensor is actually sensing knock during cranking. But I have! I've got the data if anyone wants to see it. Just email me. It's a graph showing cranking rpm,knock sensor output, and battery voltage. So what's wrong with the gauge? Probably one of two choices...either it has poor power supply filtering, or the knock threshold is set too high. As always, please feel free to present your own data if you feel my data is in error.

Dave
gnjones231@mchsi.com

 

[arista5]

it picks it up before the cranking even starts!

 

[Steve Wood]

The starter banging into the fly wheel does not cause knock. It makes a sound that contains the frequency that the knock sensor is tuned to. I can set mine off by banging the shifter into Park.

BTW, everyone else may have the same knock detector but I have three and they are each a different brand. Not having opened them, I cannot say if they are the same circuit design exactly or not altho I suspect they are pretty similar.

 

[WFO]

my starter lights up the knock sensor every time.let's me know it's working.

 

[blackbuick87]

I think everyone but Quick6 missed the worst part of his problem. If you need 110 to run 16psi his car is jacked

He either has other false knock (probably not because it goes away with octane) or some other SERIOUS problem, or a VERY high timing chip. You shouldnt need 10 gallons of 110 unless running over 20psi

 

[boostcreep]

Well, after seeing the data provided by gnjones231, it's obvious that the starter *does not* cause the knock sensor on the engine to pick up anything. It sure looks like a design flaw in the knock gauge. Live with it.

Nick

 

[FlyinGN]

I have a Fast fredie knock light and it sometimes chirps on startup and sometimes on a gear shift.. I think that they are just really sensative..

 

[ThikStik]

Remember that ther knock gauge is an electronic device made to run at a certain minimum voltage, and when 250 or more amps are going to the starter all bets are off. Its probably getting only 8-10 volts when the starter is eating all those amperes and it loses its normal brain function . Notice how lights dim when starter is energized.