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17-20 mpg?!?

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    So I have a 2013 Scion tC with about 37k miles on it. My concern is my average city drive is 18-20mpg. I do have a few performance parts in this vehicle. I'm running a Tsudo S2 catback exhaust system with CNT S pipe also with CNT headers. I do as well have a TRD cold air intake. Recently when I installed my headers I noticed I've been needing to fill up my gas tank quicker than before. I don't do additional driving to my daily routine. Today I did research and had to restart my ECU because my CEL came on due to headers. I checked what my average mpg was before and it used to run between 22-25 mpg. Ever since I restarted my ECU today and I have been driving quite I bit I've only been getting 17-20 mpg. I have not hit the highway yet since restarting my ECU so I can't tell you right now what my highway mpg is. Any thoughts of this?
    As far as I know once you reset the ECU the car has to "relearn" things like fuel trims etc., which may be why you are getting lower mpgs. You need to drive the car for awhile to get it back to normal. Your engine light will also come back on after the cars learning cycle period. Assuming your header is catless, it will come back on no matter what. My car is full catless and even with an O2 sensor spacer I still get a CEL. But that doesn't seem to impact performance based on what I've read.

    A more logical explanation for the decrease is that your foot got a little heavier because you like the way your car sounds lol. Happens to all of us. Unless you're trying really hard to drive economically.
    you know the other reasons is winter. Not that it's been THAT cold because of el nino this year. But it is colder, plus the refineries have switched over to their "winter gas" which adds in oxygenates that helps gasoline burn in colder temps, better driveability, etc. Problem is that stuff lowers the fuel economy. You might want to check your MAF sensor and clean it. People with CAI usually have more trouble with that due to air filters that are oiled, bad placement on the CAI, etc.. I know I dropped down to 16mpg before, and the problem was a dirty MAF sensor. CRC brand sells a MAF sensor cleaner.. works great! something to think about and try.
    camismacho wrote:
    As far as I know once you reset the ECU the car has to "relearn" things like fuel trims etc., which may be why you are getting lower mpgs. You need to drive the car for awhile to get it back to normal. Your engine light will also come back on after the cars learning cycle period. Assuming your header is catless, it will come back on no matter what. My car is full catless and even with an O2 sensor spacer I still get a CEL. But that doesn't seem to impact performance based on what I've read.

    A more logical explanation for the decrease is that your foot got a little heavier because you like the way your car sounds lol. Happens to all of us. Unless you're trying really hard to drive economically.



    Yeah I'm running with no cats lol. Well I was running about 17mpg before restarting the ECU. I restarted it couple days ago and took track of my mpg now city I'm doing 23-24 and highway about 24-25. Yesterday I noticed my filter from my TRD cai was in horrible shape so I went into autozone and purchased K&N air filter and I've done research that was somewhat the cause of my low mpg. I should be good for now. Also yeah my CEL came back on..
    sciontc_mich wrote:
    you know the other reasons is winter. Not that it's been THAT cold because of el nino this year. But it is colder, plus the refineries have switched over to their "winter gas" which adds in oxygenates that helps gasoline burn in colder temps, better driveability, etc. Problem is that stuff lowers the fuel economy. You might want to check your MAF sensor and clean it. People with CAI usually have more trouble with that due to air filters that are oiled, bad placement on the CAI, etc.. I know I dropped down to 16mpg before, and the problem was a dirty MAF sensor. CRC brand sells a MAF sensor cleaner.. works great! something to think about and try.
    I checked my filter in my CAI and it was in rough shape. Probably haven't cleaned or checked it in awhile. Replaced the TRD filter with K&N now I'm running 24mpg and 26 highway. Maybe it was the filter
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