I've got a 97 Ex auto coupe w/ ~90k on the Y8. I've recently changed the plugs, wires, fuel filter and seafoamed the engine.. I've got a K&N OEM square and Flowmaster exhaust.. I used to get about 275 mpt(miles per tank).. now even when driving as carefully as possible, never hitting VTEC, and all highway miles i only get about 230-250 mpt ( 25~27 mpg.)


What is killing my mileage? It still has the stock exhaust from header to cat.. and original o2 sensor...

I've thought and thought and thought about what could be causing this but i can't figure it out..

Any suggestions?

 

tire air pressure maybe

 

is the flowmaster a catback or just the muffler?

If it's a catback then your piping might be too big for the low revs.

 

no.. flowmaster is axleback.. tire pressure is mint.. brand new tires, new alignment, etc..

 

1- try taking you o2 sensor out n cleaning it off a little..

2- check you air filter

3- check the o2 sensor on your cat 2.. and see if your cat is clogged..

maybe seafoam clogged something? getting rid of all that build up..
thats my only idea..

 

new spark plug take time to break in and can decrease your mpg. it did it to me when i changed mine last. give them 500 miles or so and it should get better.

 

air filter is new K&N (<1000mi), plugs have been in for 2k, and i'm thinkin that its my o2.. i doubt my cat has gone bad already.. i haven't checked it yet though.. i'll check when it STOPS ****ING RAINING! (rained for the past week Straight... not "cloudy".. Rain.)

 

get a turbo the car isnt getting enough air to burn all the fuel

 

i say replace air filter and clean your fuel injectors

 

i say learn how to read.. its (practically) a brand new K&N.... you don't replace those for ~1000000mi. wash 'em out at 25k... also.. i've ran about 5 consecutive bottles of injector cleaner through 'em.. i'm thinkin my O2 is goin bad and it just runs it richer and richer... under hard accel i get black smoke... (which means hella rich.. not oil)


any one else with INTELLIGENT responses?