99 civic EM1 with bad gas mileage?

[bRiAnMcIvIcS]

my car has been getting some pretty bad gas mileage, 99 civic si. like 250 miles to a tank, i dont rag on my car either. i always use premium gas. i have 160,000 miles on it. i had to replace my upstream o2 sensor a month ago. maybe i didnt reset the ecu correctly? i just disconnected the battery for 10 mins. i recently installed an AEBS intake manifold, im not sure if it matters but i used the grommets off my friends d series IM they were flat, the b series grommets are kinda recessed. im talking about the grommets between the fuel injectors and intake mani. could that be a problem?
could it be tps?
fuel pump?
my gas gauge is fluctuating more than normal.:thinking:
my idle is kinda low at stop lights.
i replaced plugs with ngk about 2 months ago, dizzy cap and rotor about a year ago(not oem), fuel filter about a year ago(not oem).

any suggestions?

my stock alarm just recently stopped working also. why would that be?

[xdavidscenex]

check to see if you have afuel leak and any cels? do you have a cat? is it stock ecu?

[SOHC1]

Its that b16 tranny man...wanna trade I have an ls one? Lol

[bRiAnMcIvIcS]

Its that b16 tranny man...wanna trade I have an ls one? Lol

WTF. :screwy:

[bRiAnMcIvIcS]

check to see if you have afuel leak and any cels? do you have a cat? is it stock ecu?

stock ecu. yes i have a cat i just replaced it 6 months ago. i dont have any cels either. idk if i have any fuel leaks...i dont think so.:???:

[r_Senik]

my si with that milage is doing the same...but its weird, one week i can get like freekin almost 400 miles to a full tank, then next week i bearly scratch 300...
i think its just that we own them damned black si's..haha

[86ccord]

ah shit, mine has been getting shit gas mileage.. not sure why tho.. mines only got 105,xxx

[bRiAnMcIvIcS]

my si with that milage is doing the same...but its weird, one week i can get like freekin almost 400 miles to a full tank, then next week i bearly scratch 300...
i think its just that we own them damned black si's..haha

haha. i just wanna figure this out. i used to get like 375-400 miles a tank.
bump for some answers.:bump:

[Barefoot]

was u getting 400+ pre intake

[k3tsurui]

is your dizzy retarded?

[preferredduck]

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.

[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.

[Barefoot]

so y is he the only person with the issue and its now showing after all this time the ethanol has been in the gas.

[Batlground]

so y is he the only person with the issue and its now showing after all this time the ethanol has been in the gas.

I was just responding to the statement that someone thought it was the ethanol in the gas.


Check the ignition timing on the car as well.

[bRiAnMcIvIcS]

I was just responding to the statement that someone thought it was the ethanol in the gas.


Check the ignition timing on the car as well.

i will check the ignition timing tomorrow, that is probably my problem.

thanks for all the replys everyone.:goodjob:

[86ccord]

i will check the ignition timing tomorrow, that is probably my problem.

thanks for all the replys everyone.:goodjob:
hmm.. i need to try that also.. we shall see what my out come is..

[preferredduck]

so y is he the only person with the issue and its now showing after all this time the ethanol has been in the gas.

i have noticed this since 07, it started in gnett and now is nationwide. i got better mileage at the local winder station than the one with the ethanol sticker on it. i already had an aebs manifold on mine. then it became statewide and the chevron here in winder i always go to had to use it and i have never reached 300mpg since and i have done alot of research on this. the SI motor, esp the jdm 2nd gen b16(which i have) is very high compression and without the added evergy from the ethanol added it screws us bad. tell me how to get rid of the ethanol or safely get it where 93 octane used to be and i'll try it out. i mostly do highway driving, have turned my fuel pressure all the way down to the minimum and have trouble getting 300 miles to a tank.

also the brand of gas i found does matter, shell bp and chevron works good for me but it also depends on your area and the amount of water in the tanks too!!! my timing was checked last summer when i put a new dizzy on and afer i had my cams installed and the mileage is still the same. i think it gets high compression motors the worst. maybe i should look at a bmw forum or some other car that takes premium only and see if i notice the same thing. i think i googled this one time.