BKJJ77

i average about 200 miles a tank in my civic. i should be getting close to 400.
i cant figure out why my gas millage is so bad. I never speed or pas 3500 rpm.

I have changed the spark plugs
Spark plug wires
distributor cap and rotor
oil change
intake filter
and i use 91 gas

i dont know what to do next can anyone help me thanks

TOO MUCH TORQUE

too many factors....02 sensor is a large contributor to gas mileage. also coolant temp sensor.

purgat0ry

iTrader: (3)

Any CEL's?

BKJJ77

no cels

grumblemarc

iTrader: (4)

Not enough info.

fabioso

I believe most si cars get 300 per tank.

BKJJ77

well what other info do you need
stock header, high flow cat, mugen muffler
everyhing else is stock

motegicivic

No way 400 miles per tank, 300 will get you almost dry. Changed filter filter recently? How is the car running overall?

Andrewzabomb

air filter, fuel filter, try injector cleaner or seafoam? and i get about 320-350 per tank mixed driving with my 00 ex

BKJJ77

new intake and fule filter
my header is realy old and always looks wet after i drive my car. i think its leaking could that be something that would affect millage

motegicivic

Take off the heater shield and see if the header is cracked.

ej1ryder

Wait wait wait your header looks WET after driving your car? Something is up, a part that sees higher temps than most anythong in the car should never be wet after driving and getting the engine to operating temp. Let the car cool down and take a clean(ish) rag and wipe the "wet" part of the header. Study/smell the residue u get from doing that and tell us what you have discovered and we will go from there. Also explain to us how the vehicle runs in general. Hows its idle, is there smoke coming out the exhaust and if so what color, hows the power, does it engage vtec? Etc etc.... Pics of these "wet spots" wouldnt hurt either. And verify if its a canadian ej8 si or an american em1 si.

Edit: i assume its an american em1 from ur statement of using 91 octane. I also assume ur in california. Clarify.

BKJJ77

american em1 im waiting for my car to cool down so i can remove the header
ill take pics right now
also what should my fuel pressure be at i have a gauge ...i just want to make sure its not to high

BKJJ77

it might be hard to tell but that dark spot is wet
i think its the gasket

B serious

iTrader: (1)

Driving habits have a LOT to do with gas mileage. If you're doing a lot of short trips or letting the car idle a lot, then the mileage is going to go way down even if you never pass 3500RPM.

RPM has less to do with MPG than throttle position. More throttle position means more gas. I shift my ITR and S2000 and my GF's GSR at like 4-6k RPM during just normal driving. Usually, in 1st gear, I'll shift at like 5500RPM and then gradually bring down the RPM as I drive. Not scientifically. I just do whatever feels right. I don't pay too much attention to RPM. I usually get pretty good MPG. I did the same with my EM1 when it had the B16 and when it had the B18C-R.

The wetness around your exhaust manifold looks like maybe an oil leak or maybe an exhaust leak. If it's an exhaust leak before the O2 sensor, that could cause bad gas mileage because your O2 is reading more oxygen. The O2 sensor reading more oxygen means it's reading lean....which in turn means it will richen up the fuel mix.

If there aren't any CELs and the car makes good power and the engine is in good condition, I would look closer at driving habits and closer at that exhaust leak.

BTW, you should try actually measuring your MPG instead of just assuming MPG by saying you get 200 miles per tank. People fill tanks at different levels of the gas gauge. The gas gauge may also not be 100% accurate.

To measure MPG:
1.) Fill up to full. Don't top off.
2.) Reset the trip meter to 0
3.) Drive as you normally would till the gas tank is almost empty
4.) Fill up to full again at the SAME gas station and the SAME pump to get the most accurate reading.
5.) Divide the miles that your trip meter reads by the amount you just filled up. That gives you miles per gallon.

For example, if your trip meter says 200 miles and you just filled up 10 gallons of gas, that makes: 200miles/10gal. = 20MPG.

BryanM.

iTrader: (1)

Yeah, 400 miles on a tank would be tough to do. If OP was to average 35
mpg (I know, it's higher than the EPA rating), 11.9 gallons would net 416.5
miles at the maximum if the tank was run dry.

I believe the EM1 is rated at 30 mpg highway, which figures out to be 357
mpg maximum. 200 mile per tank would really bad mpg.

B serious

iTrader: (1)

Replacing fuel filters DOES NOT increase gas mileage. Neither does cleaning injectors. Dirty injectors and clogged fuel filters reduce fuel flow. Less fuel flow means less fuel used. If the O2 sensor sees a lean condition, it will tell the ECU to increase injector duty cycle. This will richen it up to normal fuel consumption. If the filter/injectors are REAL clogged up, it will continue to run lean till it sets a CEL for lean condition. They'd have to be pretty effing clogged up for that to happen, however.

00 EX's are going to get much better mileage than SI's. So this really isn't a fair comparison.

BKJJ77

b serious thats what i was thinking
that if there is an exhaust leak from header then the o2 sensor would be off
im going to check the gasket
also i thing i have a fuel pressue regulator
im going to start my car right now and see what the psi is

B serious

iTrader: (1)

My Si got really bad MPG for a while for whatever reason. I had a light on for a front O2 sensor rich condition. I replaced O2 senors a bunch of times. The light would go off for a while and then come back on. If I drove the EFF out of the car on the highway for a while, the light would turn off for a few days meaning that the O2 was fouling out for whatever reason. My problem ended up being my ECU. There was TSB out for the ECU on 99 Si's being too sensitive on the front O2 sensor input. That didn't, however, help MPG.

It did help MPG when I replaced my FPR with another good stock one. I think the original one maybe had an issue with the diaphragm. Maybe it was slightly torn or whatever.

BKJJ77

does anyone know what the stock psi is
and should i adjust it when car is off or on thanks

B serious

iTrader: (1)

You adjust it when the car is on and the vacuum line is pulled off to simulate WOT. Pull the vacuum line off of the FPR and then plug the end of the vacuum line so that the idle isn't raised. 50PSI sounds about right for WOT.

I think that there might be a pressure setting for closed throttle as well, though.

I don't remember the PSI...but hopefully someone can chime in.

BKJJ77

so you cant just turn the nut

RT_NEWYORK

my 2000 EM1's best mpg to date is 310, I like to put the car in VTEC and generally drive slightly faster than I should.

RT_NEWYORK

BKJJ77

ok i tried adjusting it but i couldnt even turn the bolt
and i cant use a socket becuse the gauge blocks the bolt
with the vacum hose pinched the psi was 60
and stock with hose pinched is 38-47
and with hose on the gauge read 48
and stock with hose on is 28 - 37
im like 10 psi off
i cant adjust the stupid bolt thought
i felt like i was going to break the filter any help