Battery Questions

Sal_P_510

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So, last summer I installed my first ever anything on any vehicle, which was a K&N intake on my 2017 Si Sedan. In the installation instructions, it always says to first disconnect the battery. I did so, and then proceeded with the installation. For my fist time really working on any engine regardless of what kind of job, it went well and I have a beautiful intake to look at every time I pop the hood.

Now, my real question is about the battery. After installation, I reconnected the battery, and everything was lit up like Christmas in July, and I figured that was normal since I disconnected the battery, and that there's a lot of technology within the car that the battery relies upon. The worst part about the situation was that it cleared all of my information in terms of the phone paired, the preferences I had set up for the dashboard interface, etc. but to my biggest surprise, it totally robbed me of my gas mileage that I was getting (it went from 25mpg before disconnect to 13mpg after disconnect), and I had to work all summer and winter to get it back to now 26 mpg...

So, all that being said, I would like to install an aftermarket blow-off valve to it this upcoming summer, and I'm very skeptical about disconnecting the battery, because of what happened last time.

Is there a way to keep the current gas mileage that you're already getting if you disconnect the battery, or is it going to clear the mpg's every time I disconnect it?

Thanks for taking the time to read.
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Civic17siYAY

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I would do some research on running a BOV with a MAF equipped vehicle. From what I read, venting to atmosphere messes up fuel trims.
 

SkyeSI

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In my opinion disconnecting the battery would not cause that type of drop in MPG. The PCM has "adaptives" which effect that but I really don't think it could make that much difference.

I've reset a trouble code for the "exhaust sytem problem" a few times by disconnecting the battery with no impact on MPG with my 19' SI Coupe.
 

REBELXSi

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I've reset a trouble code for the "exhaust sytem problem" a few times by disconnecting the battery with no impact on MPG with my 19' SI Coupe.
Whyd you get that code?
 

SkyeSI

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Whyd you get that code?
If you search for "exhaust system problem" you will get a few threads. It's a code that comes up sometimes, from what I've read it's a software bug and nothing is wrong most of the time. They supposedly have an update to cure it, I just haven't had time to get to the stealership.
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