Really poor gas mileage when cold.

[Perkul8r]

Ok. So I am used to having a slight drop in fuel mileage during the colder months. However my car is horrid. I usually get about 230 miles on a tank of fuel. However, it has been colder here in Montana for the past almost two weeks. I filled my car up last week, dont remember exactly which day, but I have only been able to put on about 110 miles on 3/4 tank of fuel. Only things that have changed are air temp during day/night, and the fact that I let the car warm up 5-10 minutes before work in the morning. My remote start only runs for 15 min, and I have never reached that.

I have a check engine light on, but its been on since I got the car. Its for EGR flow.

What could be causing this huge decrease on mileage? If its that bad I am going to have to park it for the winter. My 92 f250 gasser gets better mileage. lol.

Car info:
99 Legacy SUS EJ25D Auto trans. Just about 170,000 miles.
Just changed oil/filter, plugs (E3's-were given to me), wires (the better brand from Orielly's).
2nd cat has been removed, stock torque box for intake is gone, using a single tube intake from an different legacy.

Besides just start replacing a bunch of parts, is there any thing I should look at first? I need to get it figured out asap.

Thanks for any info.

[98legwag]

Possibly a vacuum leak somewhere. Also, how old is the fuel filter?

[Grimmrican]

Egr is for emissions. If anything I'd say check ur thermostat and coolant. Probably about that time it needs a flush and new thermostat. The thermostat is know to kill ur gas mileage if it's not working properly.

[Perkul8r]

Egr is for emissions. If anything I'd say check ur thermostat and coolant. Probably about that time it needs a flush and new thermostat. The thermostat is know to kill ur gas mileage if it's not working properly.

Thermostat and coolant were changed couple months ago when I put a new water pump in.

Fuel filter...I should change that. I'm unsure how old that is.

[thenines']

Fix your EGR problem-emission issues will kill your gas milage.

[Perkul8r]

Fix your EGR problem-emission issues will kill your gas milage.


The EGR code has been on for about six months now with no drastic change in fuel mileage. I know its probably hurting it, but it is not my issue right now.

besides, the egr itself has been cleaned, the tube has been cleaned. I have tested everything I could so far on that. And nothing has changed it besides replacing everything new. I would much rather go to a stand alone ems...like I am planning to anyway....and just get rid of the egr.

Onto the current problem...I did check the codes today. And I had more than I thought. I had an Evap emissions control code. Didt really give me any more info that one.

I also had an Idle air control malfunction (fail Safe) I know what that one is from. But, what does it mean fail safe? Does it throw the car into some sort of limp mode? Car hasn't been sluggish or acting funny at all.

[Wiscon_Mark]

Have you actually verified mileage by your odometer and what the gas pump says to calculate MPG?

Because the fuel tank indicator is far from accurate and I know my '95 Outback's needle would vary dramatically with different tank temperatures. It could just be the sensors being sensitive to temperature changes.

Given how many codes in different systems you have, I think you need to get these fixed before you tackle any other issues, but I do agree with everyone that's saying change out the fuel filter - it's always a good idea when you don't know how many miles are on the car, especially with the increased ethanol in winter gas.

[Perkul8r]

Have you actually verified mileage by your odometer and what the gas pump says to calculate MPG?

Because the fuel tank indicator is far from accurate and I know my '95 Outback's needle would vary dramatically with different tank temperatures. It could just be the sensors being sensitive to temperature changes.

Given how many codes in different systems you have, I think you need to get these fixed before you tackle any other issues, but I do agree with everyone that's saying change out the fuel filter - it's always a good idea when you don't know how many miles are on the car, especially with the increased ethanol in winter gas.

I haven't actually filled gas yet. Will do that today. I was kinda going by the gauge and mileage so far.

However, I cleared all the codes yesterday, and this morning on my way to work the light came back on. Only code I have is for my egr, which has been on since i bought the car. So no other codes right now. I will keep checking it though.

[Wiscon_Mark]

EVAP codes won't pop up all the time. The one on my Forester is very intermittent. Check the codes every so often to see if there's a new one in there, or clear them every time you check 'em.

[Perkul8r]

EVAP codes won't pop up all the time. The one on my Forester is very intermittent. Check the codes every so often to see if there's a new one in there, or clear them every time you check 'em.

Yeah, I have been checking it almost every time I drive it now. lol. I am going to try and clean the EGR today. We will see how that goes.

I did fill gas yesterday. And going by mileage and how many gallons i filled, I got around 13 mpg on that last tank.

But the more I think about it, if i run the car dang near empty, and fill up with about 14 gallons, even at 250 miles on a tank, thats only 17 mpg. Thats still pretty low. Or is it?

[unsullied_spy]

My 04 loses 2-3 MPG due to MT weather, winter fuel, and warm up but if you're getting under 20 MPG while driving like a sane, intelligent human being then something is wrong. Evap emissions is usually either a lose gas cap or something leaking/broken in the evap purge system.

Can you pull one of the spark plugs and post a pic of it? Here's a plug I pulled out of my Mustang after about 15k miles, yours should be similar in color:

http://i140.photobucket.com/albums/r37/Unsullied_Spy/c6fdd1c9-4489-4366-99fb-eef789bdf415_zpsf9668542.jpg (http://s140.photobucket.com/user/Unsullied_Spy/media/c6fdd1c9-4489-4366-99fb-eef789bdf415_zpsf9668542.jpg.html)

If it's darker than that or black then you're definitely running rich. Is it wet with fuel? The EGR code concerns me, if the valve itself is sticking (not a plugged tube but a bad valve) it can cause poor fuel economy but it would idle rough and it would perform poorly in warm weather as well.

What kind of MPG were you getting before it started to cool down? Was there anything else that has happened to the car in the mean time? Something that happens that suddenly is rarely good, but there's some things you can try.

Front o2 sensors are known to cause very poor fuel economy. They usually set off a CEL, but not always.

Maybe clean the MAF sensor? Your problem seems different from a plugged MAF but the cleaner is only $8 or so for a can and it usually frees up a little power and MPGs that you've lost over the years.

Pull your PCV valve and clean it out with some brake cleaner or carb cleaner. Takes 5 minutes and may free up some MPGs. It won't take you from 13 MPG to 20+ unless it is badly clogged (to the point you're pushing oil out through every seal in the engine because the valve is so badly clogged) but it doesn't take much time and if you don't have any carb/brake cleaner laying around it's good stuff to keep on your shelf.

Do you have a block heater? I put mine on an outdoor timer set to 2 hours before I have to leave for work. It reduces wear on startup and gets the engine up to temperature faster--30 seconds of idling while I scrape the snow and ice off the car and it's already moving away from the C. Your engine will run richer (more fuel, worse MPG) when it is cold and more efficiently once it warms up. How long are your trips? If you're only going a couple of miles it's normal to get that bad of MPG.

When the Thermostat was replaced was it with a genuine Subaru Tstat or an aftermarket?

[Perkul8r]

I hate to pull a plug to check it, but I might have too.

I reset the ecu and so far the only code to come back is my EGR code. However, my code reader doesn't tell me anything else besides a number. As of right now, with the egr code, my mileage seems to have come back. So far I have been able to put about 60 miles on 1/4 tank of fuel( according to the gauge). So i am thinking it was the IAC fail safe code that may have caused my poor mileage.

My MPG before this was under 20 mpg. IIRC, it was around 230 miles on a tank, and that was running it pretty low. Usual fill up was around 14 gallons. So that would put it around 16 mpg.

Car has 170,000 miles on it, and seems like its been rode hard and put away wet.

MAF has been cleaned, did that the other night. The PCV should be cleaned badly. I didn't think of that one. I do not have block heater, that i know of. I haven't looked for one yet.

And sadly, the Tstat is from Carquest. Nearest Subie dealer is 3 hours away either direction. And I had to get the car running. However, I pretest all my Tstat's after getting like 10 bad ones in a row for my old chevy. lol.

[Wiscon_Mark]

+1 for the engine block heater.

My scanguage can measure water temp and startup with a block heater is around 105* to 110*F versus the ambient temp. Not only does that mean I reach running temp twice as fast (which means I get out of open fuel loop) but it's a lot easier on the engine when the oil is warmer and flowing better. If you're unsure if you have one or not, the engine plug for the heater is located right behind the main coolant inlet at the bottom of the engine. Generally you have a cord hanging out of your lower grille like a loose tongue though :p

All of the other suggestions made are good ones. Sometimes you have to throw a bunch of parts at something to make a code go away - the joy of old cars.

[thenines']

I wish I could plug in my car at work-my 2nd gen seams to take longer to heat up than my 1st gen.(which I would only do 250 on a tank-running low on gas sucks in the winter)

[Perkul8r]

+1 for the engine block heater.

My scanguage can measure water temp and startup with a block heater is around 105* to 110*F versus the ambient temp. Not only does that mean I reach running temp twice as fast (which means I get out of open fuel loop) but it's a lot easier on the engine when the oil is warmer and flowing better. If you're unsure if you have one or not, the engine plug for the heater is located right behind the main coolant inlet at the bottom of the engine. Generally you have a cord hanging out of your lower grille like a loose tongue though :p

All of the other suggestions made are good ones. Sometimes you have to throw a bunch of parts at something to make a code go away - the joy of old cars.

So far, just clearing the codes on the ECU have returned my Mileage to normal. I still need to clean the EGR though. But otherwise, it good again. It was just kinda a coincidence that I was messing with the car and got the CEL light same time as it started getting cold out.

And its my fault I didn't even think about checking the codes. I should have done that first.