so I am seeing some really bad gas mileage after my engine swap...I had a ton of things replaced...but in particular I am wondering if it is the O2 sensors...I know my mechanic used non-OEM...he used the Denso 234-9029 Air Fuel sensors... let me know any thoughts...I am averaging about 15 or less to the gallon...highway is pretty normal...18-20 but city is very bad...10-12...before the engine swap I would average about 18 or so...

 

The computer needs to learn the engine. A reset will help. I would drive it a little first before doing much to it.