98 Legacy - poor mileage

[etc]

98 Legacy L, 150K miles, 2.2 engine, automatic

 

 

I am getting very poor MPG, even by AWD standards - 16 mpg in the mixed city driving and about 23-25 mpg on highway only at 70mph. It's drinking gas like a V8 almost.

 

I have replaced:

 

Spark plugs

Spark plug wires

Coil

PCV valve

Upstream O2 sensor

 

I occasionally get P301 and P301 misfire. Got these exact codes before the coil replacement and once after the coil replacement. Cleared the codes and it hasn't come back yet (That was 1 week ago).

 

Could it be the ignitor?

 

The power is very good, no hesitation or anything weird on the road.

[cheetah8799]

98 Legacy Outback with 2.5 engine and 5sp manual here. Since purchasing my car used around seven years ago, I have never seen better than 24 mpg. I could get 23 to 24 mpg fairly consistently when driving long distances at about 60-65 mph. In town going to work and such I would always get 20-22 mpg. In the winter (Minnesota) I would get 18-20 mpg in town.

 

So in my mind, the mpg you see is in range with my vehicle. However I have seen posts from guys getting 25+ consistently. You have the 2.2 engine though.

 

My 05 Outback 2.5i with 5mt gets 25-26 consistently, touch better on the highway trips around 65mph.

[The Chad]

I've got the same car as you do, '98 Legacy L, 2.2 with 155k. For reference, I'm getting above 25mpg consistently with about an equal mix of city and highway driving, so something's gotta be up.

 

How long has it been getting this poor mileage? Even though you're not getting the 0420 and 0325 codes, have you checked the cat and knock sensor? It's unlikely, but could be you're feeling the effects before it triggers the CEL if it's just been a short time since the drop in mileage occured. My knock sensor was cracked and I'd gotten a cylinder 3 misfire code that dissapeared after replacing the knock sensor.

 

Did you use genuine Subaru plugs and wires, and did the 0301 occur before you changed the plugs and wires? How about swapping the cylinder 1 and cylinder 3 plug wires with each other to see if the misfire follows. Misfires are often wire related, so ya never know. Maybe use some dielectric grease when putting the wires back on.

 

You'd said the power is good, but can you tell any power difference since your mileage drop? I'm wondering if cylinder 1 really is misfiring if there is no loss in power?

[etc]

I replaced plugs and wires last winter, with OEM Subaru parts.

 

The P301/302 occured this spring and was very consistent. No loss in power or anything. I got a used coil and the codes went away almost completely. Did occur once after the coil swap and not again.

 

The mileage improved somewhat after the O2 sensor change, also OEM part. I went from 23MPG on the highway to maybe 26.5 mpg on the highway. The in town mileage, in D.C. traffic is still fairly abysmal, went from 16mpg to maybe 16.5 or 17mpg after the O2 sensor swap.

 

However, some anecdotal data: we also have a 99 OBW, auto, 2.5L, I don't drive it but I know it consistently gets 29mpg or so and it's a bigger, heavier car with bigger engine. 200K miles on it.

I suspect a 2.2L/auto can get high 20's in top condition.... this one is a bit beat up.

 

Plus I have a major oil leak, camshaft seals and more. It smokes bad at stoplights sometimes. I wonder if that contributes somehow, though it shouldn't.

 

I haven't had P301/302 in a couple of weeks now....

 

 

How do I check the knock sensor and the cat?

[ericem]

well you can check the knock sensor to see if it is cracked. Remember the engine does make a vacuum in the oil system and i guess supposedly it could create a air leak. Hook up a vacuum guage should be a steady 21hg.

[Hendrik]

Different car , same principle , (mine 1,8 1993 , auto as well)

Black smoke , black exhaust , lots of petrol.

Changed 2 weeks ago one injector , now petrol is only going at half speed.

[OB99W]

Plus I have a major oil leak, camshaft seals and more. It smokes bad at stoplights sometimes. I wonder if that contributes somehow, though it shouldn't.[...]

Sometimes oil leaks are due to excessive blowby (exhaust getting past worn piston rings), especially if the PCV is clogged, so check that. If the smoke is bluish-white, that's oil burning. If enough oil is burning, it can effectively reduce octane rating enough to cause knock, which in turn can cause the ECU to retard ignition timing, and retarded timing will reduce performance and gas mileage.

[greenleg88]

MEEE TOO! im excited to hear an answer on this thread....

[OB99W]

It's possible for a defective engine coolant temperature sensor to incorrectly report to the ECU that the engine hasn't warmed up when it actually has, and leave it running open-loop. That will definitely kill gas mileage.

 

What's the idle RPM?

Edited August 28, 2009 by OB99W

[michaelbteam]

The best mileage I ever got was 27-28 in mixed conditions from a beat-up manual 1990 legacy wagon with 200 k miles. A 93 automatic legacy never got better than 22, my 96 2.2 manual outack gets about 25, but our automatic 97 outback with 225 k also gets 25. They all have run fine so I've not tried to tweak tuning. Seems like they are all just different.?!

[etc]

Today again I got codes P301, 302,303 and 304 - misfire on all 4 cylinders. It's intermittent.

 

I replaced the coil (with a used unit), could that be the issue? Or anything else could cause P30x codes?

[mike97]

i have a 97 suby legacy thats the same with me .i am getting 27 to 29 mpg and crap on the highway ..and black smoke out the tail pipe .when i go down a hill and then steep on it the smoke acures .i looked around and my egr valve isent working .not going in an out .i must have a vacume leak or egr needs to be cleaned or a new one ..the egr valve cane haunt ya to.

[GeneralDisorder]

Change the plugs and wires.

 

GD

[Fairtax4me]

Yesterday I got 33 out of mine solely highway. 55- 60 the whole way on a 120 mile round trip. I was quite impressed to see such a high number.

You've got a few things working against you. First it's an automatic. Second you drive in the DC area.

 

Intermittent misfires on all 4 could mean a number of things. Could be a coil, could be bad fuel, poor connections, moisture in the spark plug wells causing the spark to jump. You could have a vacuum leak, a ruptured fuel pressure regulator, a bad or dirty MAF sensor, lots of things.

 

I;d start by checking the vacuum hoses (there are a few that can be quite the pita to get to), clean the MAF sensor, and maybe run some strong fuel injector cleaner in the gas.

 

Couldn't hurt to make sure your plug wires are seated correctly.

[STI_Wolf]

for the poor mileage it might be a dirty mass airflow sensor.. you can get cleaner for it at any auto part store pretty much.. electrical parts cleaner works too, but not as well as the actual mass air cleaner.

 

do NOT use brake cleaner or carb cleaner!

 

 

Also, air filter might be dirty

 

i dont know about the other problems though.

[Bigbusa]

does your AT temp light flash right after you start the car and then go out?

 

Do you have torque bind? If you do, it'll kill your MPG because your car is basically stuck in AWD all the time. My impreza is lucky to get 18 mpg because of TB.