Extreme decrease in MPG
 

Ok so after installing my AEM CAI on my 05 AT rx8, the thing drinks gas like an alcoholic drinks beer. So before the intake, i was getting 16mpg with city driving. And now im getting maybe 10mpg or less, i have not actually calculated it but after about 15 miles from a full tank the gauge will drop 2 tick marks. Obviously this is not a very good way to try to calculate mpg, but i have been sort of afraid of driving it too much with it running so rich. I have reset the fuel trims and the MAFS is clean. I have tried to search the forum for answers but i couldn't find anything about the mpg dropping so low.

Since you already addressed the potentially introduced problem points that I would have directed you to, I would recommend that you not only let this tank finish, but then wait for the 2nd tank as well, and then see where you are at.

The most likely cause at this point is that 15 miles could easily not be enough for the fuel trims to be settled yet, and you might have been running a lot richer than normal.

The second most likely reason is that the auto-shutoff for that fuel pump shut off earlier than you expected, and it didn't actually top up the tank. It might only be down by half a gallon to a gallon, but that will make a remarkable difference in the first bit of driving.

If the first tank finishes around 10mpg, or after the second it isn't much better, then there is something deeper wrong.

Will letting it run that rich for two tanks cause any more problems? Thanks for the response.

Posted From RX8Club.com Android App

For a short period of time, I do not see it being a problem. I would just do what RIWWP said and address the issue after 2 tanks if the issue remains.

Ok. Will do. Thanks guys. I will update after the two tanks.

Posted From RX8Club.com Android App

This. One pump shut off on me with 1/4 of the tank left to fill. I figured the station just ran out of premium, because I haven't had a problem since. I have noticed certain stations pump nozzles fit into the car differently, some go in quite a bit farther a likely kick off sooner.

Sorry for taking so long to update but i have been busy. The mpg are back to normal. I have no idea what the problem was. Guessing the trims were not fully set up yet. Thanks for the input guys.