99 civic EM1 with bad gas mileage?

[Batlground]

i have had 2 si's, one new off the truck in 2000 and it got 3-350 miles per tank all the time, i bought my current one in 04 and it got around the same mileage. i also have an aebs manifold, header, exhaust, hollowed cat, CTR cams etc, and i can get 300 miles to the tank now only after i turned my fuel pressure to the minimum of 30 psi. i think it's the ethanol in the gas honestly. i remember when they started to add it at certain gas stations and everytime i used that gas my mileage was crap. also in 01 kentucky had ethanol in the gas and the same thin happened then. now all gas is 10% ethanol and as you know our high compression motors require premium and since ethanol does not have as much energy as gas i think that is where the problem is. i noticed this before i put the manifold on my car so it's the only thing i can think of. you may need to adjust your timing and idle since you put the manifold on but i don't think it's anything you did.

i have also noticed the mileage drop in other cars also so i really think it's the ethanol in the gas. also sometimes the brand of gas matters. shell and chevron ahve done me well but my girl added wal mart in one time and it was crap, so i think there may be several variables here. also BP is pretty good. QT is ok, but last week i filled up with shell and got rather good mileage while going 85ish on the interstate.

It most certainly can be the ethanol in the gas. The cars computer cannot detect it and it has to add more to get it to maintain the proper fuel ratio. You can get it tuned out but with the ethanol content changing in the gas all the time its hard to keep up with it.

[Barefoot]

It most certainly can be the ethanol in the gas. The cars computer cannot detect it and it has to add more to get it to maintain the proper fuel ratio. You can get it tuned out but with the ethanol content changing in the gas all the time its hard to keep up with it.

that cant be true. if it was ever car on the road that wasnt flex fuel would be getting bad mpg. i know my stock 91 accord is getting 32 mpg still with the 10% ethanol they add.

[Batlground]

that cant be true. if it was ever car on the road that wasnt flex fuel would be getting bad mpg. i know my stock 91 accord is getting 32 mpg still with the 10% ethanol they add.

Unfortunately, it is true. You may not notice it but that doesn't mean its not happening. Think about it, you need 30% more ethanol than gasoline to maintain the same air fuel ratio. When you add 10% of ethanol to gas the computer has to add 3% more total fuel through the injectors to compensate for the 10% in ethanol. We have tested cars on the dyno from 10% ethanol to 90% ethanol for a special project that we have been working on.