This may sound stupid, but are you actually doing the math on your fuel economy or just trusting the display's economy numbers ?



If you have an android phone, I suggest aCar. There are free and paid versions, but for what you need the free version will work fine. You do have to enter your mileage, fuel quantity and cost per gallon in every time you fill, but after a few months of reviewing, it will give you accurate idea of what your fuel economy is.


I posted this info on another fuel economy post, but here's a very ugly csv cutout of the fuel data as you record it

You can see that it will update the fuel economy when I do my next fill for the previous fill, but you can see I'm getting like 19/20mpg with mixed driving. You can see with my mileage listing that I am getting like 200-225 to a tank.

 

You should get it checked for sure

 

I had thought of that as well. In the old days when running older cars-trucks etc it was one of the first things a guy would do as well as a fuel filter.

I called South Coast and they informed me that an O2 sensor or disconnected EGR hose would for sure throw a CEL. And that isnt the case for me.

Car seems to run fine. Just gets horrible mileage now, when I was getting 27-29 on the Highway and 21-23 combined in the city.

What plugs do you recommend? Back in my WRX days I used to run good copper plugs as they ran hotter. Only downside was they had to be changed out annualy.

Any suggestions?
Thanks

 

I don't see how worn spark plugs are going to all the sudden reduce your mileage by 30%. That and you said the car runs fine otherwise. I'd be looking elsewhere if I were you.

The stock plugs are Iridium and I think most suggest to stick with the OEM NGK's. I don't even think they offer another replacement that isn't iridium. They didn't for the IX's.

Replace your clutch and see what happens.

 

Bad plugs would be the result of mis-fueling, not a cause. It's likely that there's a failure in the delivery, causing over-delivery. Whether that's a vac. leak from a regulator, or a programming issue/electrical failure causing over-delivery.

Anyhow that poor of fuel economy and if your not WOT every chance you get sounds like you should be seeing signs in your exhaust, on a wideband, etc.

At this point I would suggest doing lots of self-diagnosis and not relying on a dealer to figure out a problem while it gets worse.
-- Revert to stock
-- Check for physical damages (vac hoses, leaks, etc)
-- Check for abnormalities in run condition under controlled conditions
-- Document what you check and when, and document your actual fuel fill amount and refill amount per mileage. Double check your mileage against known good markers and distances.


I mean, what if this is a case where your favorite gas pump is illegally under-fueling you and the same $40.00 or whatever is only giving you a fraction of the fuel it claims on the pump. OR what if the odometer in the car isn't working correctly and the 150miles it's showing is actually 200miles.

 

Im def NOT WOT all the time. In fact, since Ive been back out here Ive been just commuting back and forth to work. Not even spirited driving.

No sticky tires either (Conti DWS properly inflated).

Car is bone stock not one modification period. Dealer maintained.

The two delears even within range of me have been horrendous over the phone and dont even seem interested.

I think Im going to give the car a good going over tomorrow. Then locate a good tuner that looks at these cars everyday for a living.

Thanks everyone....

 

I've been getting 28 MPG for the past week on the hwy. Strange! Kind of awesome though, haha.

 

Hey thats very helpful. Im glad.

Typicaly I get that....27-29mpg on the HWY. Until now I guess. I havent taken it on the HWY sonce I started getting this terrible mileage. Maybe I should do a short road trip just to check it out....

 

I'm on a filthy rich tune and I'm averaging 10mpg per tank.

City driving I get 8 or 9mpg. Highway around 14. I need a retune. If you drive behind me your eyes will burn.

 

That's not tuned, that's broken! If someone touched your fuel trims and you're like that (even making 400+whp) They are trying to destroy your cylinder walls, plugs and make a mess of everything.

Even on an alternate fuel like E85 you should be like 12-16mpg. I would seriously check if you have a stuck injector or broken regulator. And for the sake of the F.S.M. Stop driving your car like that.

 

These are good points. My fuel injectors were changed along with fuel rail, lines, regulator, and fuel pump.

 

Sorry to drag up such an old post, but I thought this experience might still be relevent.

Since moving to CA Ive been getting terrible mileage as previously mentioned. I drove down to SC Mistubishi and had them scan the car (great service BTW), and they found nothing wrong. Zero. And I was practicaly begging them to work on the car.

What they told me was: CA has terrible gas (duh), and that during the winter they switch to a "Winter formula" that doest burn as efficiently. Hence the poor mileage.

The irony of this is using the poor quality 91 octane "winter mixture" I get much worse mileage than I do using the higher 93 octane that the selfish, anti-environment states use. I would think CA would want to see me get better mileage, hence leaving a smaller "Carbon footprint."

But what do I know?

So far Im averaging 17-18mpg in the city, and 23mpg on the HWY.

Elsewhere in the country I average 21-23mpg in the city with spirited driving, and 27-30mpg on the HWY depending on weather etc-

 

So your saying you get the advertised gas mileage for the car?

Yea I normally get around 20~23ish in city driving based on the way I drive. Like you said, prolly just crappy 91 ****-tane CA gas, and the winter gas at that.

 

The way they make gas crappy is by adding ethanol. AZ has the same fuel as CA, usually. By default "Premium 91octane" is actually E10. It used to be (in the 90's) that summers would have straight 91 and winters were E05, then around 2003-04 it started going E05 Summer and Winter. Then, around 04-06 it was E10 Winter with E05 Summer. I don't think they can go E15 as then the (Mon+Ron/2) octane formula we use in the states will drop below 91 and then they can't advertise it as such.

Not saying that you couldn't of gotten a bad tank or two of gas depending on where you're filling up, because I definitely avoided some stations in Orange County because of bad gas. But, I would still keep watching your economy and keep interesting in finding a better solution.
17-19mpg though, that sounds fine. I average 19.2 on the same crappy southwest 91 octane and If I did a lot more stop and go I could see it falling to 18.

 

throw the MBC away, why are you using that?