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Does anyone know how a knock sensor works, what it monitors, is it sound or vibration ??
 

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Knock Sensors
Implementing a knock detection/control strategy requires sensors to monitor the combustion process and
provide feedback to the engine controller. Knock sensors can be classified in two broad categories: direct
and remote measurements.
Direct Measurements
Pressure sensors measure the pressure inside the combustion chamber of a running engine. This direct
measurement of the combustion process provides the best signal to analyze to detect engine knock.
However, each cylinder requires its own sensor, and individual sensor costs are still relatively high. As a
result, pressure sensors are used primarily in research settings. Currently, Toyota is the only manufacturer
that installs pressure sensors in production engines. Pressure sensor usage will increase in the future as
sensor costs are reduced and automotive companies develop more sophisticated engine control strategies
that monitor the combustion process.
Remote Measurements
Remote measurement sensors use vibrations transmitted through the structure of the engine to detect knock
in the combustion chamber. The signal received by remote sensors can be contaminated by sources otherthan engine knock, which increases the difficulty of signal detection. This is especially true at higher engine
speeds in which background mechanical vibrations are much higher, effectively reducing the
signal-to-noise ratio. One advantage of using remote sensors is that, with careful placement, only one or
two sensors are required to monitor all cylinders. In addition, the sensors are less expensive, primarily due
to a less harsh operating environment.

Hope this helps answer your question.
 

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Stanggt00,

Do you know of anyway to bypass the knock sensor on my 05GT?

Thanks,

Retr05
 

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But why would you want to?
 

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If i get anywhere near redline on 1-2 or 2-3 shift, motor falls on it's face. Feels like some kind of governer is applied cutting power in half!!! Frustrating when the stupid fart mobile passes like u r standing still! I think the knock sensor system is backing cams or ign timing off.
 

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It should only be backing timing off if it senses detonation. If that's the case, maybe more timing isn't the way to go.
3V's are prone to pre-ignition (and the valvetrains aren't stable up high). There isn't a whole lot you can do about it save some aggressive head work.
 

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But why would you want to?
Some superchargers will have vibrations that can trigger the knock sensor when there is no knock.

If i get anywhere near redline on 1-2 or 2-3 shift, motor falls on it's face. Feels like some kind of governer is applied cutting power in half!!! Frustrating when the stupid fart mobile passes like u r standing still! I think the knock sensor system is backing cams or ign timing off.
What is the fuel pressure doing during that?
 

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Ah yes, those things are very sensitive to NVH inputs. Good call!
 

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It's to bad that the Ford Knock sensors can't be re-programmed like the ones on a GM. The GM one's work really well.
 

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I just want to test my theory that I have a "super sensitive" knock sensor. I believe this to be the case because the car has been doing this "fall on its face" thing that I mentioned since brand new with factory tune. I need to isolate this problem to solve it, and want to start with free$ and easy. If I pull the lead off of the knock sensor will the car start? Heck, do you know where the knock sensor is located?
 

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You'll throw a code for sure. There are two sensors...one for each bank (even though only one is needed). They are located under the intake, in the valley of the block.
 

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The output from a knock sensor is an audio signal.

Two resistors per sensor can be used to "adjust" the sensitivity.

Cut the signal wire, and install a series resistor. On the ECU side of the resistor, connect another resistor to ground, to bleed off some of the signal. The bleed resistor is also known as the load resistor.

If the resistors are equal value, the signal to the ECU will be cut in half.

Someone was making something like this for GM sensors a few years ago, called the Knockout Box, but it looks like it's gone.

Here's one I just googled ("knock sensor"desensitize):
http://www.charm.net/~mchaney/knock.gif

The above circuit is for GM one wire sensors. which have an internal resistor (3.9k or 100k). I doubt if the Ford two wire sensors have an internal resistance measurement.

Donut style sensors require high value resistors, since they can't drive much of a load. For these type sensors, try 510k ohms minimum for the load resistor.

Donut style sensors have two wires plus a shield. One of the wires is usually grounded internally at the ECU, the other is the signal wire.
 

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Thanks 01steed, Thanks John...
To test my theory I have asked Brent White (Brenspeed.com) to write a custom SCT tune to remove the knock sensor from the equation. John, if this isolates the problem, I'm going to Radio Shack with your plans in hand. BTW...Brent was able to write an SCT tune that accomodates my new 4.88 gearset (I have a T-56 trans). The SCT only goes up to 4.56. The tune worked out well.
 
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