Sudden Drop in MPG

[Steel Armadillo]

Hey guys. I've got a 2003 with the 3100, just rolled over 190k. Its been well maintained oil/air filter/everything else at regular intervals. The only mods are an empty cat and SLIGHTLY upsized tire (very slight). The fuel filter was replaced maybe 15k ago.

Up until 3ish months ago I was getting consistent 420-425 miles to a tank. Now all of a sudden I'm getting 350-360 miles. No significant changes in driving habit.

Anyone have any ideas why?

I have tried (with no effect):
New air filter.
Seafoam in intake (not in fuel).
High-end gas in last two tanks.

Thanks,
-Jesse

[blueguy]

Any CEL's?

Also...what about the weather? Has it gotten pretty cold recently? Because hotter weather = better MPG's

[Wisconsingrandprix]

boost bypass stuck??

[blueguy]

boost bypass stuck??

To answer this...I'm going to reply with the very first sentence in the OP's post...

Hey guys. I've got a 2003 with the 3100

[Steel Armadillo]

No CELs. Sorry, forgot to put that in OP. I can put a tester on it just to see if something comes up, either tonight or tomorrow.

[Steel Armadillo]

I didn't see the second question Nick, it has been blistering hot here since May (Central Florida). The last two weeks maybe it has been slightly more bearable.

[Steel Armadillo]

I don't like to bump my own thread, but I could use input.

[00SilverGTP]

I had a drastic drop in mileage too. Got er narrowed down to my upstream O2 sensor. May be the same issue on yours. Not sure if the 3100 runs an upstream and downstream O2 setup or just a single. But its definitely something to look into.