Terrible MPG! Help!

I have a 2008 legacy GT and love it... But I am getting terrible MPG right now, about 16-17. First of all I don't think this is normal if so let me know. What could be some causes of this if it isn't normal? O2 sensor? I read something about those and how they can effect your fuel. Any help would be much appreciated!

Right foot is the biggest factor in MPG. All city 15-17, mix 19-21, all highway 27-30.

 

I'm 40\60 cty/hwy. Drive normal, avg. 25.2mpg, heavy on the boost, 22.7 mpg, long highway tips 28.8 mpg. My avg, mpg is 24.6 for my 120 daily commute.

 

Mechanical part that can effect MPG's, bad, dirty or worn out, MAP sensor, air filter, fuel injector, spark plugs, coil packs, O2 sensors, CAT's & your tune that you're running.

 

Mike

I agreed with all of the above...You probably dont have a mechanical issue. Ease off the right foot.

I wish it was as easy as lifting my right foot... I have been easy on the gas and still get 16 average mpg! I will look into those things you said may cause this. Thanks for your help hammer down.

Did you just acquire this car or do you have a history of its MPG? Does it now have or has it ever had any mods?

Ive had it for about 2 months now and its been around 16-17 MPG ever since I bought it... the only mods is a SPT cold air intake, full exhaust, and coilovers.

Are you tune for you mods. This cars needs to be tune for any that not stock. For air entering the motor & exhaust exiting the motor before the mid pipe. IE; SPT cold air intake & full exhaust .

 

Mike

Could also be useful if you took some logs and had someone look over them to see anything out of the norm.

I bought my '05 LGT new and I never saw better than 17 MPG. It was one of the reasons I decided to get rid of it. The non-turbo Legacy gets great mileage, but I guess there is a tradeoff with the turbo in that regard. I can get 25 mpg out of an '09 Rav4 V6 all day long. Different vehicle obviously, but still.... If I can get 25 on average out of a vehicle with the same or more power and is quite a bit heavier, then I am just surprised I can't get that out of the LGT. At least, that was my experience with my 05.

What kind of driving are you doing as well? I routinely see 18-19 mpg when I don't drive on the interstate for a week or two. If you have a relatively short commute to work, don't spend much time on the highway, and/or your car doesn't get much time to warm up, the mileage you're seeing seems totally reasonable.

 

I have never understood why people buy this car with 250-300 hp (depending on model year and tune) and are then surprised it gets similar gas mileage to that of a V8 of approximately the same model year putting down similar power.

@OCD ... 4 more years of technology, completely different drivetrain, and the Turbo ... umm ... encourages fuel consumption at RPM well below that of the NA RAV4. And as for weight, the RAV4 weighs in right around 100 lbs heavier comparing slush-box to slush-box.

 

The biggest advantage there is the extra 4-5 years of technology.

Yeah, I didn't really look at the weight numbers. I just assumed it would be heavier because of the size. But the technology doesn't really matter too much on this one I don't think. The '06 Rav4 V6 got the same gas milage as the 09 I'm comparing it to. I think it is the turbo that is eating it all up. You see that all the time when comparing turbo cars to NA cars with similar performance numbers. You sacrifice fuel economy to get the faster 0-60 and 1/4 mile times. Not that I mind. If I was looking for a fast car then fuel economy isn't necessarily on the top of the list of things I care about.

 

It just goes back to the basic three things you get to choose from and only get 2 of them: Fast, Cheap, and Reliable. You only get the three choices and can only have two, so what are you willing to sacrifice? I'll take Fast and Reliable any day of the week compared to what you get with the other combinations.

I can't wait to see Subaru's new direct injection turbo boxer motor... It's crazy what DI can do for gas mileage and power.

 

Turbo Cobalts are getting over 30mpg IIRC.

 

FYI I average about 21 MPG as well

Are you tune for you mods. This cars needs to be tune for any that not stock. For air entering the motor & exhaust exiting the motor before the mid pipe. IE; SPT cold air intake & full exhaust .

 

Mike

 

Actually u don't need a tune for the spt intake as long as u have a stock row pipe and up on it.

 

 

-Mike Paisan

 

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The rav 4 and any commuter based car will get better mileage due to gearing.

 

On my SVX I could turn 28-30 mpg easily on the highway at 75+ mph. My sti would get 17-18mpg at those speeds.

 

The issue is that final 5th or 6th gear ratio. On a turbo Subie it turns 3500rpms or more. On my 335 at 80 it turns 2500rpms with 300hp and gets 26-27 mpg at 80.

 

Most toyotas and gm cars turn very low RPMs in the top gear and get great mileage.

 

 

-Mike Paisan

 

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Yes turbos and boost eat your mileage... but the poor boxer motor is what it is. When I used to drive all turbo mitsubishi's, in fact, my most powerful car had a mega large turbo that would spool only by 4500-5000 rpm. I daily commuted still and actually got 27mpg. When I got on it (375 awhp) I could see the gas gauge drop all by itself (850cc injectors).. yikes. I had the impression when I went stg 2+ on the subie it would help mpg, but it really stayed about the same, just that I got a lot more power out of it. I do mixed highway/city and get 21mpg all day long, maybe even 23 when it hits summer and I don't get on it. When I use it to go back and forth to the grocery store on the weekend and drive the kids round.. 15-17mpg

I can easily make my 335 drop down to 13-15mpgs if I am in the boost and driving like a maniac. The problem with the turbo subies I found from owning a few over the years is that in the speeds I drive 75-85 it is constantly in the boost so you blow through fuel at an awful rate. If I dropped down to 60-65 then I could get 24mpg on my STi on the highway.

 

-Mike Paisan

 

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Tires can contribute 1-2 mpg also.

Tires can contribute 1-2 mpg also.

 

Yup that definitely has an effect as well.

 

-Mike Paisan

 

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there's also a threshold around 130-140 kph where the car will tend to transition to open loop fueling more easily. iirc the transition delay is set to zero when the threshold is exceeded. same holds for engine rpm. around 3500, the transition from cl to ol gets a lot easier.

 

these cars can get decent mileage if you move CL targets lean of stoichiometric and adjust timing to match. the real limiting factor is that you can't really target leaner than ~ 15.5 while staying CL. some years back I tried a bunch of experiments on the CL targets to see how far you could push them while staying CL. around 15.7 to ECU drops out of CL.... well that and the gearing

 

 

I can easily make my 335 drop down to 13-15mpgs if I am in the boost and driving like a maniac. The problem with the turbo subies I found from owning a few over the years is that in the speeds I drive 75-85 it is constantly in the boost so you blow through fuel at an awful rate. If I dropped down to 60-65 then I could get 24mpg on my STi on the highway.

 

-Mike Paisan

 

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Gearing, rolling resistance of the tires and tune can greatly affect your fuel economy. I routinely get 28 to 30 MPG when I am doing mostly highway miles in my spec B. My old car was a JDM V8 swap (with the spec C vf36 turbo). There are quite a few differences between the setups, and I had trouble reaching 20 MPG in the JDM 2.0L regardless of whether I was driving highway or city miles. There are a few major differences though.

 

1. Gearing. At 2500 rpm in 6th gear, the spec B is already over 110 km/h, the JDM sti (with the JDM 6 speed) was only able to do about 90 km/h at the same engine speed. Obviously, driving anywhere from 100 to 130 km/h I could get better fuel economy based on the slower engine speed being 1 factor (better aerodynamics of the GT vs the WRX help a bit too).

 

2. Tires. On the Spec B, lower rolling resistance, lower grip tires that were on the car when I bought it actually got better fuel economy then the higher grip Pilot Super Sports I have installed now, even though the when and tire combination on the car now is 20% lighter in weight! I was surprised to find this, but it seems that lower rolling resistance tires can improve your fuel economy by around 5%. I am not going back to lower performance tires for fuel economy reasons though, so I will just have to live with the loss in fuel economy there

 

3. Maintenance. Keeping up with the maintenance, in particular changing the oil, keeping the air filter clean and cleaning the MAF, changing spark plugs on time, periodically checking the PCV, fuel filter and O2 sensor will help maintain good fuel economy. I have noticed noticeably worse fuel economy when the MAF was dirty and when my throttle body was sticking a bit, cleaning restored original fuel economy in both cases.

 

4. Tune. The tune of the JDM sti is much different than the USDM model. I am not even sure that it even has a closed loop mode. The car always stays feeling very responsive at all RPM, but the fuel economy suffers. The twinscroll vf36 is slow to spool compared to say a TD04 at low RPM in low gears, but in higher gears (still in higher RPM due to gearing) it spooled without much noticeable delay. This fast spooling at highway speeds means great passing power at all times, but it also seems to be one of the things the gave me poor fuel economy at all times too.

 

5. Driving behavior. The key here for most people is to let the car slow down a little when going up hills and let off the gas to coast when going down hills. This minor change in driving habit can often give you 2 or more MPG vs. how most people typically drive.

I get about 21MPG in my 2.5i, and most of everyone I know with an LGT close to stock get's the same as me. But I city drive a bit.