A while back I had a problem where the car would struggle going 3k rpm at 50mph and got 19-20mpg .

I had the catalytic converter changed and the throttle felt great, got 26-27mpg and was excellent.

Over a period of 2 weeks i saw the mpg drop when calculating it each time i filled up to where it is now at 20mpg and sometimes hitting 22 if i'm lucky. Their has been no difference in driving styles when i was getting 26-27mpg and now. The engine is starting to slack again but it's not as bad as it was as i stated up top.

I've done seafoam and had no difference. Some guy at chevy said it could be the muffler as it sometimes goes after the cat dies.

Any ideas? 2000 v6 a4

 

same here, i'm only getting 17 mpg in the city and only about 22 mpg on the highway. Full tune up and fuel filter and sea foamed it and everything but nothing. i can't figure out why it is doing this. the only thin i haven't changed are the injectors. what would cause such bad gass mileage? sry, no trying to high jack ur tread lol.

 

Its cool. Another guy I talked to said it sounded like my injectors are acting up, but that wouldn't make sense if I was getting excellent performance and 26mpg after changing the cat.

I might chop the muffler off and see what it does.

 

Have you gotten a check engine light on when this problem is occuring? Is the car misfiring or is just feels like it has no power beyond a certain point?

 

No codes, no misfire. Compared to when it was getting 26mpg it feels sluggish, lack of performance and thorttle response.

 

Check your O2 sensors.. My car didnt have SES come on, but I scaned anyway and it was my 1 of my sensors.. Check the wiring to them also.

And your getting between 20 to 27 mph.. Im lucky to get 16 to 18..