Knock Retard
Thread Starter
TECH Apprentice
Joined: Apr 2005
Posts: 319
Likes: 1
From: North Carolina
Knock Retard This may sound crazy, but can someone explain to me what knock retard is, and how does one know when it occurs? I ask this in reference to an issue with my Y pipe and the knock sensor.
TECH Enthusiast
Joined: Mar 2003
Posts: 618
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From: San Diego
Your knock sensor is like a stethoscope on the engine block. If it hears pinging, preignition, detonation, etc. it pulls timing depending on how much noise it hears. If your y-pipe isn't clearanced or mounted correctly and it bangs when you hammer the throttle that 'bang', if strong enough, can be sensed by the knock sensors and the pcm will think its detonation and pull timing. If you want to know for sure, run your tank down to near empty, put like 3-4 gallons of 101 octane in and see if it still pulls timing. If it does, then it is false knock and not something in the engine.
a banging Y Pipie will not cause false knock...
teh knock sensors are not just looking for loud noises...
they are loking fo ra very specific noise...
a noise that can only be caused by knock or ping
teh knock sensors are not just looking for loud noises...
they are loking fo ra very specific noise...
a noise that can only be caused by knock or ping
Originally Posted by mega squirt website
Spark knock is the sound of abnormal combustion in an engine. Once combustion in a spark-ignition internal combustion engine is initiated by a spark, the flame front is designed to spread from the spark plug and travel across the combustion chamber rapidly and smoothly. As the flame front propagates across the chamber, the remaining unburnt air-fuel mixture can ignite spontaneously (auto-ignites) before the flame front arrives, due to the increasing pressure and temperature in the combustion chamber. When this occurs, there is a sudden jump in the pressure in the cylinder. This causes in the characteristic knocking or pinging sound. Knocking results from ignition timing that is too advanced for the fuel octane rating and operating conditions at that moment.
The knock sensor is tuned to a specify frequency, like a tuning fork. When this frequency is applied to the sensor (through its connection to the engine), a peizoelectric crystal inside the sensor generates a small voltage (~1 volt), much like a microphone. As an example, some Corvette knock sensors (GM PN 1997562, 1997699, OR Standard Motor Products KS45, KS46, KS49, or KS117) had a design frequency of 5200 hertz, and they would produce a signal between 4800 rpm and 5600 rpm
The knock sensor is tuned to a specify frequency, like a tuning fork. When this frequency is applied to the sensor (through its connection to the engine), a peizoelectric crystal inside the sensor generates a small voltage (~1 volt), much like a microphone. As an example, some Corvette knock sensors (GM PN 1997562, 1997699, OR Standard Motor Products KS45, KS46, KS49, or KS117) had a design frequency of 5200 hertz, and they would produce a signal between 4800 rpm and 5600 rpm
i had a buddy of miine with a banging y-pipe and everytime he pulled off from the light the computer picked up 8* of KR. he welded a valve spring to the spot where it hit and the KR was gone. So yes it is possible for the PCM to pick up a banging y-pipe as spark knock.
Thread Starter
TECH Apprentice
Joined: Apr 2005
Posts: 319
Likes: 1
From: North Carolina
If the PCM pulls timing, Will you feel it lose power, or is it something that you would need a tuner in the car to notice. I ask because sometimes when I hammer down, I can feel a thumping in the floor board under my feet. Now in looking at the Y pipe, I looks like there is plenty of clearance. I dont hear a bang, but i can feel a thump. It also seems to do it more when its cold. If I drive it for a while, It almost totally goes away
