Without exact measurements, that could be accurate given what you describe.

Depending on conditions I'd see 12MPG (pure city tank in Chicago winters) to 30MPG (all highway with a light foot) out of my old 2003.

 

I'm in Pa and I think the bitter cold snap has also been a factor! Tonight I'm driving until the gas light comes on, then filling up, then planning on driving to a half tank, fill and calculate.

I'll do no idling, just strictly town driving to drop off my 3 year old at my aunt's daily and run some local errands in the evening. Without the idle factor, but on winter gas, what would be an acceptable range for me to hopefully see?

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Just looking at my E46 BMW mpgs which also has a 2.5 engine in it and I'm only getting 18.5 mpg this winter in her. She gets an easy 10+ min idling each morning as the morning temps have been in the single digits by 9am. Gotta keep the little guy warm!

Idling really seems to kill mpgs!

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Idling even an hour a week killed my mpgs by a good bit. A ~2mpg difference doesn't sound like a lot but it adds up with a near 17 gallon tank.

 

Yea on 8.4 gallons, idling for at least 3 hours, as I did coolant system refreshing, power steering flushing and engine bay cleaning made my mpgs in the 14-15 mpg range. I filled up full last night and have 62 miles on the tank already and the needle barely moved.

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Ok, so after filling up and driving 112 miles, here's where my gauge stands...

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The verdict is in after driving 188 miles.

My mpg comes to 21.6.

That is local roads with one stretch of highway for 20 miles. Everything else was up and down Pa country roads and a short drive to drop off my little guy each morning.

Seem reasonable? Also, I have to figure in the gas is currently strong winter formula with all the cold weather we've been having here in Pa.

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My MPGs are about the same. Looks like you're doing decent gas-wise.

 

Awesome. What do you get on a pure highway run?

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When I went to Utah last year I got 27-29mpg. Probably could have been better if there weren't hill climbs. I'm in the Phoenix area so going out of town means hill climbs of some kind. Lol

 

So I had to follow up...

After running another tank of gas, this time I only got 17 mpg. This tank was strictly around town. Short trips. Lots of starts and stops. But, my dad has a 2001 outback sedan with 310,000 miles and he just got 24 mpg with similar driving.

I'm at a loss why mines so terrible. I've scanned the car, no codes. Nothing pending. Coolant temps are perfect in the 180s and 190s. So I know the coolant temperature sensor is doing it's job.

What else could help improve my mpgs even though I don't have a cel? Under normal circumstances, the cel would tell all. Stumped here.

Here's what's replaced:
Plugs
Wires
Air filter
Fuel filter
Oil only has 900 miles on it
Starts and runs great!

The only thing I do notice is it runs rich. I can smell it in the exhaust even after it's warmed up.

 

A DTC (Diagnostic Trouble Code) is only set when the ECU detects a sensor is out of specification (either a out of spec reading or no communication with the sensor). Once a DTC is set the Check Engine Light is illuminated to advise there is a problem and is a warning to the vehicle owner to get the vehicle to a workshop for diagnosis.

Not every problem with a vehicle sets a DTC (flat tyre, empty gas tank, blocked fuel filter, low oil pressure etc)

If your vehicle is using too much fuel you need to connect the OBD2 port to a scanner that can read live data and either log the data or read the data as it occurs. This should help to diagnose the actual reason why the vehicle is using excessive fuel.

One of the things to check and fix is the battery cables and ground/earth cables. These all need to be clean, corrosion free and tight. Many problems that occur to a Subaru are related to poor electrical connections and @cardoc made a great post in the last few months about a vehicle that arrived at his workshop with excessive fuel consumption and after cleaning all the earth/ground connections the vehicle returned to normal fuel usage.

Seagrass

 

Thanks seagrass.

Tomorrow I'm going to use my obd2 live reader and see what's up.

What specific data points should I be looking at to narrow down why I'm running rich.

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My suggestion to anyone not comfortable with interpreting live scan data...

1. Record a data log of all or most pids when your Subie is at it's best for future comparison.

2. Go to pidfusion, upload a data log of your sick Subie and compare it to your 1st healthy data log (best case scenario).

3. If you skipped step 1, then the next best thing is to upload and compare to someone else's healthy Subie.

 

I'm wondering if the valves are not set to spec on my car. The previous owner said she lost her harmonic balancer and continued to drive it and killed the heads and some of the valves. I have receipts for all the work including new valves and whatever that entails.

Could it be possible the car just wasn't specd correctly? 17 mpg driving short drives/around town just seems too low. My dad, who albeit drives like an old man and is an old man of 73, is getting consistently 24+ mpg. I do live in a more hilly area though then him and his daily drives are longer then mine.

Also I'm using torque. Which data should I be logging? I have to choose what to log.

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If you compare logs, you should be able to determine if the poor mileage is due to the engine, driving style, or a combination of both.

I've seen poor mpg complaints after a louder muffler was installed. It turned out that the extra noise influenced the drivers foot on the gas pedal.

 

And upload here

 

Thanks tdubs! The car definitely has a complete catback new exhaust system, but it's junk napa. I loathe Napa parts.

I'll do some logging this week and see what happens. I'm also going to give my dad the car for a tank of gas and see what sort of mpgs he gets.

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Ok, so I officially filled up today and after 278.1 miles, I got 18.6 miles per gallon. This was strictly all local driving in cold weather with winter gas.

I am noticing my long term fuel trims are in negative though. My 60 mph long term fuel trim is around negative 7%. So for some reason the ECU is reducing fuel...

 

I wouldn't look too far into any fuel trims that are single digits, negative or positive. What are they at idle?

 

I wouldn't look too far into any fuel trims that are single digits, negative or positive. What are they at idle?

At idle they are -15% or greater. Here's some live o2 sensor I logged today...

I'm leaning towards my upstream sensor is bad.

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Today I installed a new upstream oxygen sensor and sure enough the old sensor was bad. I can see the voltage fluctuating as it should with the new sensor. The old sensor was stagnant!

My fuel trims while driving are now between -1 and 3%. Not perfect, but getting there. Much improved of the -7% I would see while driving with the old sensor.

I am however still seeing high negative fuel trims at idle. They are around -9 to -10%. Previously they were -15% at idle. So, things are improving but not cured. I've checked just about everything else vacuum wise and can't find a thing wrong/unhooked/leaking. It's all solid.

I believe with the new 02 sensor, I should see some much improved local driving gas mileage. I am hoping to get 21-22 at the very least.

Any other suggestions on what still causing my negative long term fuel trims at idle?

 

If an O2 sensor gets you better economy I may just do the same. Since gas hit $4/gal yesterday fuel economy got a bit more important to me. Typically 19-21 mpg in the last couple months.

 

How about it!

I'll keep you posted on mpg. I have a lot of idling so far with this tank so things are skewed somewhat already.

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17MPG for a pure winter city tank is reasonable to me. I'd get 16-20 for a city tank depending on conditions. Best I ever got in our old 2003 on the interstate was a 32MPG tank. But that was a long interstate trip with the CC around 65MPG, roof crossbars removed, and tires +8PSI over the doorcard.

 

17MPG for a pure winter city tank is reasonable to me. I'd get 16-20 for a city tank depending on conditions. Best I ever got in our old 2003 on the interstate was a 32MPG tank. But that was a long interstate trip with the CC around 65MPG, roof crossbars removed, and tires +8PSI over the doorcard.

Definitely interesting how mpg differs. My dads 01 sedan with 310,000 miles gets 24-25 mpg consistently. He drives a mix or highway and town.

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Well after resetting the battery so the ECU could reset all it's adaptations, I'm happy to report my fuel trims while driving, are impeccable.

The upstream 02 sensor replacement was just what the Subaru doctor ordered! My long term fuel trim at idle though is still in the negative, hovering anywhere between -2 to -10%. I'm not going to worry about that. Here's my numbers while driving.

 

How much has fuel economy improved?

 

B1S1 is the upstream sensor? B1S2 is downstream? Making sure I'm looking at the right sensors on my Bluetooth app.

 

Yes, that is correct.