I got in an accident about a year ago and it jacked up my A pipe in my exhaust (the part that takes the headers from 2->1), I replaced it with a cheap ass something, and same deal with the cat (cheap), and put in a Bosch O2 sensor.
Other then that it’s completely stock Honda exhaust

Since then MPG has been on the suckie side, and I think the cause might have to do something with the fact that each pipe in the "OES" pipe is 1/4 inch smaller then stock (that is the two pipes that go to 1 are 1/4 inch smaller EACH).

Could this be the cause? it’s taken me a long time to put 2 and 2 together. Also I think its running a little rich, as my tail pipes are covered in black soot.

PS its an EX so I’m rocking the 4-2-1’s