I own a 2017 bmw m2 n55 engine manual. I changed my waterpump and thermostat bc veh overheated and codes showed it. While changing this I decided to upgrade my intercooler for a bigger one and a sport catalyst. I noticed my mpg drop somewhat. I decided to buy a bootmod3 tune on my laptop and flashed the ecu with it to a stage 2 map. My mpg got even worse. I reflashed the ecu to stock oem and put back oem intercooler and catalyst. All in all my mpg is still really bad, I watch the needle drop as I sit idle in my driveway. I tested the car in the higway and when I put the car in sport+ my mpg gets better, or should I say at high speeds. At low speeds my mpg drops significantly!! Any thoughts? Thanks
Edgar Zhanay
NY
Okay you change the cat. You start changing OEM BMW parts without having the software reprogrammed for them. You're going to have problems. Those BMWs are so complex. You can't just start putting things on. You'd have to find a BMW expert mechanic or a tuner who could make adjustments. And most tuners really don't work on BMWs. Good luck though!
