I have a 2018 Subaru Legacy 3.6R. I removed both mufflers to install a hitch. While the mufflers were off, I ran it for about 30 seconds. The problem is that my fuel economy has decreased by at least 3 mpg. All of the connections are tight and the car idles and runs like normal. The check engine light has never come on. What could be the problem?
I'd do another tank or two of gas and/or weeks before I'd do something that drastic. Perhaps you might get a scan tool (Scotty recommends Blue Driver - see upper right corner, under Tools). Then you could see if everything affecting mileage (and other stuff) is within spec.
Oh, solved old thread, … but I chime in , anyway!
He removed mufflers, dickered around with the exhaust system. He probably disturbed / damaged - somehow - O2 sensors! And now, … computer is fiddling with STFT and LTFT. I bet that’s what causes the fuel consumption discrepancy. Just scan for those, … see how they graph.
F.S.
Yup, that’s what I was wondering too. Something with the O2 sensors post the muffler work.
OK, thanks for advice. I will check it out.
Lower air temperatures reduce gas mileage - longer to warm up the engine, which requires a richer fuel mixture, more air resistance because cold air is denser. Every car I have had has worse gas mileage in the winter (10-15%), and I live in a moderately cold state - Maryland.
I understand your point now, however I haven't experienced any decrease in mpg in cold weather in the 3 years I have owned it until this event. Do you think a computer reset would help?
Yes I think you should wait a few tankfuls to let the computer readjust, or you can fasten the process by disconnecting the battery & resetting the computer back to factory settings.
Honestly though, if the car ran fine otherwise & no codes, I’d just let it be & enjoy that Legacy to the fullest.
3mpg is nothing major to go around & start spending $$$.
Also, have you already checked all the basics like cold tyre pressures, air filter, etc?
How about adding some Fuel Injector Cleaner to the next tank?
Doubt it’s anything to do with the fuel delivery itself.
I did add fuel cleaner and that changed nothing.
Was the outside temperature the same?
What are you asking me to compare the outside temp to?
@italiantom, he means what was the temperature the same before & after the muffler instal? Referring to cold weather loss of mpg.
Yes the temp was the same.
Did this occur only after removing the mufflers to install the hitch?
Yes.
I haven't heard form you in a few weeks and would like to hear form you. Thanks.