Extremely Low Gas Mileage!

[dmlemus]

So In the last 3 weeks I've noticed I am substantially getting less gas per tank on my rex. I used to get about 275-280 per tank and now it only gets about 165-170. I've done all the regular maintenance but the pcv valve and fuel filter. I just ordered them from Honda. Would like to know what other culprits could it be? Any Help?

[95_civic_gsr]

O2 sensor

I'd also run a can of BG 44K fuel injections system cleaner through it.

Also, did you recently buy new tires?

[dmlemus]

Originally Posted by 95_civic_gsr

O2 sensor

I'd also run a can of BG 44K fuel injections system cleaner through it.

Also, did you recently buy new tires?

Change the O2 Sensor in may to pass smog.

I bought new tires 2 1/2 months ago, but didn't have a problem until 3 weeks ago. I keep track of mileage at every fill up and 3 weeks ago I noticed the drastic decline of gas mileage.

[95_civic_gsr]

I once had a set of tires that dropped my MPG by 7 Miles per gallon! From 38 mpg to 31 mpg dropping my miles per tank from about 420 to 340. Did you go with wider tires or stickier ones? If they are wider or softer, they will amplify your cars alignment problems, and will show more as the tires wear down.

But your 10-15 MPG drop sounds more like you aren't burning your fuel efficiently. Plugs, plug wires, distributor cap, rotor, fuel filter, air filter, pcv. Is your check engine light on?

[dmlemus]

Originally Posted by 95_civic_gsr

I once had a set of tires that dropped my MPG by 7 Miles per gallon! From 38 mpg to 31 mpg dropping my miles per tank from about 420 to 340. Did you go with wider tires or stickier ones? If they are wider or softer, they will amplify your cars alignment problems, and will show more as the tires wear down.

But your 10-15 MPG drop sounds more like you aren't burning your fuel efficiently. Plugs, plug wires, distributor cap, rotor, fuel filter, air filter, pcv. Is your check engine light on?

I have 205 tires falken azenis. two months I bought the tires.

ordered new ngk plugs, dizzy cap and rotor were changed...just ordered fuel filter and pcv, did an air filter change as well.
And no CEL. weird

[sdlEF]

fuel pressure regulator could be bad.

[dmlemus]

Originally Posted by sdlEF

fuel pressure regulator could be bad.

okay, I'll check it and see if I also replace it.

When I initially noticed the low gas mileage 3 weeks ago I did a spark plug change and on the 3rd plug chamber I did notice some oil on the spark plug thread. Would a bad spark plug seal cause low gas mileage. I just ordered this with the valve gasket...will see if this helps.
I think i was pushing the car a little hard on the freeway.

[Robb]

Besides the usual stuff... how about clogged cat ? bad 02 sensor ? use an OEM paper filter if you have a K&N.

205/50 15 is not stock OEM overall diamter tire size.
Your RPMs would run lower which in turn should give you better mileage !

195/50 15 is closer to stock size (185/60 14)

[dmlemus]

Originally Posted by Robb

Besides the usual stuff... how about clogged cat ? bad 02 sensor ? use an OEM paper filter if you have a K&N.

205/50 15 is not stock OEM overall diamter tire size.
Your RPMs would run lower which in turn should give you better mileage !

195/50 15 is closer to stock size (185/60 14)

I did replace the O2 sensor in may, I am not getting a CEL reading now. But will check. I haven't check the cat...

well...first I am going to do all the maintenance stuff that is left to do, and see what happens.

[rexerin]

sometimes your ECU will throw a code without your CEL being on (or your CEL bulb could be out)... take a peek under the carpet and see if you get any blinks, if you haven't already.

[SiRMarlon]

It's the Ski Rack on top of your car Dani!

[dmlemus]

Originally Posted by SiRMarlon

It's the Ski Rack on top of your car Dani!

LOL

I thought so too, but I had the rack way before I noticed the change...bought a fairing to detract the wind.

I think my car is running a little rich with the blown spark plug seal, will change and see if there is a difference,

[dmlemus]

Originally Posted by rexerin

sometimes your ECU will throw a code without your CEL being on (or your CEL bulb could be out)... take a peek under the carpet and see if you get any blinks, if you haven't already.

Looked under the carpet to see if there was a blinking red light and nothing.

I've change my plug wires and I am currently waiting on several other things from Honda to replace. so I'll see what happens.

And thanks guys for all your help!

[95_civic_gsr]

Originally Posted by Robb

205/50 15 is not stock OEM overall diamter tire size.
Your RPMs would run lower which in turn should give you better mileage !

True that circumference of the tires are larger, which means more distance traveled per revolution of the engine. However its changing your gear ratios to and can mean much more work for your engine. Also your odometer doesn't know that you changed your tires/wheels. So it will report fewer miles per tank if you've increased your tire size, even if you are actually covering more miles than before.

It could be lots of little factors that add up.
Wider tires make more wind drag, the location of that drag is amplified.
Wider tires also create more friction with the road surface.
The weather's temperature change can also have its effect. (though colder weather usually = better fuel economy, unless you filled up in hot weather)

@ OP
I'm NOT saying that its YOUR TIRES for a fact. It just may be a factor. It was for my car. You might be surprised at the results if you swap out some tires with a friend, at the MPG difference.

[dmlemus]

Originally Posted by 95_civic_gsr

True that circumference of the tires are larger, which means more distance traveled per revolution of the engine. However its changing your gear ratios to and can mean much more work for your engine. Also your odometer doesn't know that you changed your tires/wheels. So it will report fewer miles per tank if you've increased your tire size, even if you are actually covering more miles than before.

It could be lots of little factors that add up.
Wider tires make more wind drag, the location of that drag is amplified.
Wider tires also create more friction with the road surface.
The weather's temperature change can also have its effect. (though colder weather usually = better fuel economy, unless you filled up in hot weather)

@ OP
I'm NOT saying that its YOUR TIRES for a fact. It just may be a factor. It was for my car. You might be surprised at the results if you swap out some tires with a friend, at the MPG difference.

I get what you are saying, but I just noticed the mileage change on 10/24/2009. I bought my new tires on 8/31/2009...so i've been on the road with these tires for two months. first month I had the tires one it was running straight.

I filled up my tank today and added the BG 44k, will see if this helps.
If I were to change my oe fuel pressure regulator with a B&M will this potentially help my fuel economy?