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So a while ago i cleaned my egr passages and did a bunch of maintenance on my insight. While putting everything together i noticed something. My knock sensor was broken. The sensor housing had a split in the plastic and could be divided in two pieces. The plug still attached. I put the two pieces back together and had no codes. The best mileage i could get on my drives was in the 52 mpg range all sub 45mph. It didnt throw a code for the knock sensor mind you. So i just got around to ordering a new one. Installed it and am already noticing a couple of interesting changes. After the idle learn procedure just before the fan came on the engine suddenly got a lot quieter. I'm pretty sure it was because the ecu was adjusting the timing based on knock readings and had finally gotten it right. Now even at idle the car is quieter. It has more power across the power band. The most interesting thing is that now my car seems to use less assist in situations where it used to use more and now i regularly see my mpg gauge go into the 125mpg range and have no trouble maintaining speed while in that range. I find it particularly interesting because there was no real warning that the sensor was bad. If i had not noticed the physical failure of this part i would have had no idea it was actually bad. Just a heads up. I cant make any guarantees that this is a fix for low mpg but it helped me a lot.
 

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A knock sensor is basically a microphone bolted to the cylinder head that "listens" for predetonation. Damage to the plastic part of the sensor has no impact on its performance, so long as the electrical connection is intact.

Predetonation damages an engine, so if any is detected, the timing is retarded. It shouldn't have any effect on your fuel economy. I'm pretty sure you're looking at noise in your fuel logs, unrelated to your knock sensor.
 

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Who know's, maybe his knock sensors plastic being broken was causing it to pick up noise that was retarding his timing and wrecking FE. I just fixed a knock sensor CEL the other day on my buddies 04 civic, I thought the sensor was bad but while I was about to replace it I noticed the old one was loose, causing it to vibrate and pick up all sorts of noise. Tightened it back up and the CEL hasn't come back.
 

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I know I’m digging up bones here but I think the difference you spoke of was not the sensor but rather the clean plate. I cleaned mine up. Was totally plugged up and after was much more responsive and quiet. MPG really went up noticeably as well. The knock sensor I installed is garbage too. I’ve been noticing it’s constantly throwing codes.
 

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What codes is it throwing?
 

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Are you monitoring the timing from a gauge such as peters OBDIIC&C or something else?
 

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Is there one besides the actual Honda sensor that works well? Considering the ima pack is going I think I’d rather invest in a k20 swap that gets the same mileage or better than I’m getting now.
 

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When I get back from Insight Fest, if someone wants to experiment PM me and I will mail you for free a S2000 knock sensor, it has a different part number but looks exactly the same. You can like try it and see if it works. It would be good for us to know if it magically did work because it costs way less. I'm afraid it might not though -- it may be calibrated differently somehow.

I'll mail it for free you just gotta promise to try it out on an Insight and, crucially, report back to the forum with your results.
 
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