Bad gas mileage. Suddenly

[maria24017]

I'm sorry for all my questions.. It just seems like it has been one thing after another.

I had put a few gallons of gas in the car a couple weeks ago and drove nearly 70 miles before the gauge was on empty. On Sunday I put $10 in, which should have been slightly more than 3 gallons. 57 miles later and I ran out of gas while crossing a lane of traffic (nearly getting hit). The gas gauge said about 1/8th of a tank, so I give up on that.. But I intend to pull the cluster and replace the low fuel light bulb.

Since the fuel gauge isn't working I may have had even more than 3 gallons in the tank on Sunday.. So I got at the MOST 19 mpg. Before pulling the engine and everything it got around 25 mpg.

Codes that it is running are canister purge solenoid, knock sensor and throttle sensor.

The knock sensor was replaced, but it never stopped running the code.

I was thinking the throttle sensor code may had been a result of the issues we were having previously with the car acting like it was running out of gas, although the code didn't show up until a while after the problem resolved itself..

I have tried clearing the ECU by disconnecting the battery as well as pulling the 14 fuse and neither worked.

Any ideas why I would suddenly be getting bad gas mileage?

[Legacy777]

Maria,

Based on past experience, you need to replace the canister purge solenoid. Sometimes these cars will not clear stored codes unless that is fixed. My hunch is because it's an emissions related issue.

I'd suggest replacing the canister purge solenoid, perform the active code diagnostic with just the green connectors (instructions are on my site), and see what comes up. If nothing comes up, then try clearing the codes again using both the black & green connectors while following the instructions on my site.

Regarding the low fuel light. Have you tested to make sure the bulb is burned out? These instructions show you how to "force" the low fuel light on. If it doesn't come on with the instructions, then you know it's the bulb, and not the mechanism in the tank.

http://main.experiencetherave.com/subar ... pdiag1.jpg
http://main.experiencetherave.com/subar ... pdiag2.jpg

To fix your gas gauge issues, you'll likely have to replace one or both of the fuel senders. I had to do it with my Legacy a couple years back. Both senders were bad.

Regarding your fuel mileage, fill the tank up all the way, drive the car until it's almost empty, and then fill the tank up all the way again. Filling the tank up all the way is the only way you'll get a reasonable estimate of your fuel mileage.

[91Beater]

Your discrepancy may stem entirely from bad measuring method. Full is the only near constant value you have.

How far you let it down before you fill effective makes the "integration period" or the duration of averaging. The longer it is, the better the approximation.

[Flatfourced]

Look for the real reason for the knock sensor code. Most likely a broken wire. I have seen it more than once.

Also try to clean the surface where the sensor mounts on the block.

A knock sensor code will cost power and fuel mileage.


good luck!

[evolutionmovement]

I echo the above. Limp home mode from a knock sensor fault will be noticeably bad mileage.

[maria24017]

I filled it up a few weeks ago and kept a couple gallons of gas in the trunk. It started running out at 325 miles on Saturday.

How many gallons are legacy tanks? I have found conflicting information

[Legacy777]

15.9 US gallons is what the owner's manual states.

http://www.main.experiencetherave.com/s ... ns/118.jpg