Bad Gas Mileage?

[CAV3MAN227]

-So I've been getting bad gas mileage for at least my last three tanks of gas or more. On average between those tanks of gas, I've been getting 12-13 miles per gallon. I don't know why! I can't even hit 200 miles anymore on one tank of gas. (I only use 91 btw)
-I've thought of some things it could be, bad injector, bad gas, leaky fuel line, winter fuel, etc. I've replaced the fuel filter and coolant temp sensor. That didn't change anything. The iacv has been sticky lately, hanging high idle. Always having to kick the throttle. When the car idles correctly, my afr's are, with warm 800-900 rpm idle, 14.7-15.2. So that to me seems normal. What else can it be?
-Motor is all stock, td04 turbo, custom intake with stock svx air box with a k&n filter, 06 tmic, gfb bov. 02 wrx trans and diff swap, 3.9 gears.
-Any help or ideas is appreciated, thanks.

-Joe

[cj91legss]

Interesting, I just noticed my 93 is getting 14mpg. I'm considering parting it out...

[macipusy]

Sounds like time for an ECU upgrade and a real tune. I was getting 10 mpg on stock injectors, ECU and 91 octane. After standalone, 550cc and E85, I was getting 12mpg and I think close to 20 mpg on pump gas.

[cj91legss]

My 93 is 100% stock.

[mike-tracy]

My fuel economy is down to 21 from 24. I attribute it to winter gas and letting my car warm up for 5-10 minutes every morning

[turbo970]

winter gas sux

[killajamal]

I'm with mike. Winter mix sucks. F the machine! \m/ \m/

[CAV3MAN227]

-I still think there is something else messing with the mileage.
-I'm thinking of finding the needed diagrams/pics and pulling the manifold and replacing everything, breather lines, vacuum lines gaskets, etc. I think the iacv is the culprit.

-Joe

[James614]

I remember my gas mileage dropping in the winter, but I think 16 was the lower I ever saw (18 was normal). A lot of things factor in: crappy winter mix, extended idling, more obtuse traffic patterns, drag from snow on the road, etc. If all your regular maintenance items and tire pressure look good, I wouldn't sweat it too much.

[James614]

I just re-read and saw you're getting 12-13mpg. That does seem pretty low even for winter. Plugs look good? MAF dirty? No low tire pressure? O2 sensor working?

[CAV3MAN227]

-12.64 mpg on this last tank. Just filled up tonight.

-Spark plugs are new, maf has been cleaned, coolant temp sensor replaced, new fuel filter. O2 sensor will most likely what I'll go to next and see what happens then. If nothing, probably going to pull the manifold and just replace everything. I still need to chase the fuel lines and make sure I don't have a leak anywhere. Maybe get a set of fuel injectors too.

-Joe

[Legacy777]

Try sucking air through the IAC valve hose/tube. There is a little check valve there to prevent boost from blowing through the IAC valve. If it's damaged that may be a contributer to the poor fuel economy.

Here's a pic of the valve.

http://main.experiencetherave.com/subar ... P_5107.JPG

[cj91legss]

I'm going to part mine out, when I get to that point, I'll look at that diaphragm and see if it's my issue.

[James614]

That valve is a big gotcha, hardly anyone knows it's there. I found out about it chasing down the reason for persistent boost leaks when I got my 550 tune running. But at the time I replaced it, too much had changed to be able to tell if it affected fuel economy.

[Legacy777]

Yeah, that valve is not widely known about. I replaced mine because it was starting to tear & crack.

[CAV3MAN227]

-I think I may have found the leak, the rubber fuel line thats like two inches long just before the fuel pressure regulator, I believe in it is, on the passenger side fuel rail, just in front of the turbo. I can't 100% confirm it yet as I need to pull apart the intake to have a closer look. Saw nothing out of the ordinary from underneath the car, so thats good!
-I'll have to take a look at that iacv check valve thingy. Does anyone think thats a part that Subaru would still stock?

Joe

[James614]

They had them in stock when I ordered mine around April-ish. I don't have the part number handy though.