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2012 Mazda 3i GT
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A lean code after installing a CAI generally means either its not installed correctly and is leaking somewhere downstream from the MAF or the intake tubing is not sized correctly.
If its sucking in air downstream from the MAF, that air is not being read by the sensor. The sensor will only provide information on the air that flows past it, and the ECU will deliver fuel accordingly. When the leak is downstream from the MAF that will register as lean because there is only enough fuel for the air that is read by the MAF, and anything that enters the intake downstream from the MAF will lean the mixture out.
If the tubing is sized wrong the intake velocity will be wrong, so the readings from the MAF will be wrong and fuel delivery will be also wrong accordingly.
Yea but the weird part is that after refitting the intake and resetting the ecu the car runs fine, perfect ratios good fuel trims and then after five ish days or so it goes to shit. So its reading it correctly for a bit but then it changes its mind. I did a vaccuum test and I can’t find any, FTS B1 is at 0 on idle and doesn’t go to outrageous numbers.
 
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