what is a knock sensor for

 

It's like a microphone that's tuned to listen for knocking sounds in your motor. If it hears something it will let your ecu know so it can adjust the timing accordingly to save your engine. If your Knock sensor goes bad or you unplug it, your computer will automaticly pull timing from the engine which cuts back the power quite a bit.

 

detects knock/detonation in the engine... http://auto.howstuffworks.com/ignition-system1.htm

 

the stock knock sensor is worthless, if anything get an aftermarket one that has a readout/screen so you can see the severity of the knock and at what rpm it occurs.

 

i have a jdm d15b swaped from a usdm d16y8, the y8 harness has a knock sensor but the d15b block dose not have a place for one anawhere on the block. so its just hanging there. is that why my car runs like it weights a few 1,000LBS more.

 

Yes

 

do you know if the p28 will solve my problem?

 

any help. what should I do to solve this problem

 

I was going to see get the correct ECU for your setup, but I am not good with that area yet. You have to get one that doesnt look for the Knock Sensor, and for me the option was to change over to older OBD system. PM user "Luserkid" on here, he is very good at this.

 

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a knock sensor can go anywhere on your block or even on a bracket, say the alternator bracket, get creative, hint alternator bracket =P