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Discussion Starter #1 (Edited)
knock/temp/ preshure sensor question

hello guys, i was wondering, how a knock sensor works, is it possible to use a knock sensor to activate a solenoid to inject water at a high boost or load (as an emergency system)? i don't have a knock in my engine, just pondering for a future engine... also what type of switches are available that will "flip" at certain induction vacuums or pressures?
 

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Knock Sensors

Your detonation sensor "Knock" is designed to retard the timing when you run into detonation "spark knock" conditions. Remember the old "Pinging" noise on acceleration? If it's working it should stop that. You can take your timing light and while watching your timing mark have someone to tap around the sensor and watch it retard the timing.
So you do not want to tap into the wiring of this sensor and create any resistance problems because you will probably end up with timing problems.----------
 

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Discussion Starter #3
no no, i dont have one in anything i own, infact i never even seen one! newest car i own is a 1970... i dont plan on using a knock sensor for its intended purpose, rather to create a signal somehow to energize a solinoid operated valve..... BTW where do they mount knock sensors?
 

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The sensors are screwed into the block where the pit****s or plugs are, just above the pan rail.
 

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I've recently discovered that noisy timing gears will also set of the knock sensor. Its a handy and safe thing to have however I am not running mine. I wasn't going to risk snapping off the coolant drain plug in the block to install it.
 

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they work by the piezeo-electric effect(pardon my spelling?) a "ping", or spark knock causes vibration in the coolant which vibrates a chrystal in the sensor causing an induced voltage. the EST circut in the computer anylizes this voltage signal and retards the timing accordingly with a table of set parameters.
 

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Discussion Starter #7
humm, so i supose it would be almost impossible to rig it up to energize a solinoid... humm
 

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Old School Nut said:
humm, so i supose it would be almost impossible to rig it up to energize a solinoid... humm
The knock sensor will not directly operate as a switch. If you're sharp with electronics it could be made to supply a signal to a circuit board which at a desired output from the knock sensor would use a transistor to send power to a water injection pump. Or it could pick a relay that would power the pump if the transistor and circuit board couldn't handle the load.
 

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sbchevfreak said:
they work by the piezeo-electric effect(pardon my spelling?) a "ping", or spark knock causes vibration in the coolant which vibrates a chrystal in the sensor causing an induced voltage. the EST circut in the computer anylizes this voltage signal and retards the timing accordingly with a table of set parameters.
Some may work this way, and I am no electronics genious, but not all do. The sensors that I am familiar with are basically just a microphone. For the ECU to work properly with the knock sensor the fequency of generated by the knock has to be known. The gear drive setting it off is an example of a poorly tuned ECU or one that was not designed to work with the gear drive in the engine. I hate to sound like a salesman, but the vems Genboard V3.1 has the ability to "listen" for knock and I am sure that the developers would add the simple hack to enable one of the spare outputs that are now activated by RPM, MAP and a few other modifiers.

Here is a link to instructions on how to make a knock listener that you can use yourself or could add a mic plug and plug into a laptop to record the sounds if you so desired.

http://www.vems-group.org/index.php?page=KnockListener

Chris
 

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There are two main parts to the knock detection. First is your sensor, second is your ECU module that interprates (sp) what the sensor is picking up. In my '95 Firehawk I have an LT-1 sensor, but I swapped out the knock module for an LT-4 module in the ECU because it's more accurate than the LT-1 module. As for wiring up some sort of injection system off the module itself, yea, it's possible but I can't tell you how to do it. I might not reccommend it either as false knock would activate your injection system and could cause damage.
 

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Discussion Starter #11
humm, thanks for the info guys.
 

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Here's a simpler way to do what you want. Use an adjustable vacuum switch that closes when vacuum drops. Plumb it to full manifold vacuum and wire through an oil pressure safety switch. This way the water injection would only run when the engine was under a heavy load. The oil pressure safety switch would ensure that it would only pump water when the engine was running.
 

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Discussion Starter #13
Tresi, well i went to the parts store today for such a switch. the parts guy didnt know where to start looking! do you know a spicific vehicle that might have one that would work? i would think their are many out their.
 

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Alot of guys use what is called a hobbs switch to activate thinks like water on turbo engines. They can be set to close the contacts at a certain boost range. You may be able to get a switch like this that is designed for vacuum instead of boost.

My local Carquest carries Hobbs switches, but I have never looked close at them to see the range. They are on the shelf with the guages.

Chris
 

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Discussion Starter #15
cool thanks Chris! i will have to go to the parts store and check it out.
 
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