Odd Mileage Issue

[geckoboy86]

The Issue
Ok. My mileage is messed up. I get just under 16 city but I can get 26 highway. I don't understand it.

How I Drive
My city driving is about average, not to much of a lead foot. 1st Gear is the only gear to go over 3k RPM. When I do drive hard, mileage seems to only be affected by a small fraction.
Highway is all Cruise control set around 70 (Revs just above 2750 RPM).

About My Car
95 Subaru Legacy L with 2.2L

Car has 190k on it and catback is only about 50k.
Age of Cats are unknown, Age of O2s are unknown.

No Oil leaks, does burn some through the exhaust.
The car runs smooth. Idles at lights just above 500 RPM.

CELs P400 and P420 have been on before. The P400 is currently on for the EGR Valve but it was replaced and the current one does move. The P420 was for O2 but it only came on randomly, last occurrence was over a year ago.

Engine has been sea foamed. Spark plugs and wires are only about 10K old (NKG). Intake setup is an SRI hybrid with snokus delete.

Help
So, What should I look into to get these numbers up (more so the city)?

If I forgot any piece of information, just let me know.

[harrymaneuvers]

How far away from your work do you live?


I used to get great city mileage when I lived 13 miles away from work. Now that I live about 1.5 miles, my city mileage went down because the distance I am driving before starts/stops has significantly decreased.


I couldnt figure it out for the life of me... until I had a chance to spend a week NOT driving to and from work... then my city mileage mysteriously came back to normal. Then as soon as I started driving to work again, mielage dropped again.

Do you have a scangauge?

[geckoboy86]

How far away from your work do you live?


I used to get great city mileage when I lived 13 miles away from work. Now that I live about 1.5 miles, my city mileage went down because the distance I am driving before starts/stops has significantly decreased.


I couldnt figure it out for the life of me... until I had a chance to spend a week NOT driving to and from work... then my city mileage mysteriously came back to normal. Then as soon as I started driving to work again, mielage dropped again.

Do you have a scangauge?

Im about 8 miles from my work. its about a 10-15 minute drive.
Only electronic tool I have is an ODB2 reader.

[Huffer]

Maybe your math is at fault?

Typically, the EJ engines and 90s fuel maps take awhile to kick in. You get better economy when the engine is at operating temp. That should take about 2-3miles of moderate driving in the winter (sub 40F). In the warmer climates, the engine should be at operating temp within 2miles (50F+) with moderate driving.

[geckoboy86]

Oh. Its been like this since I got the car in 2009. Its been slowly getting worse. Doesn't seem to matter what season it is, though winter seems to be a little harder on it.

EDIT: just rescanned my car. 3 codes. P0400, P0420, followed by another P0400.

[Huffer]

Time to clean out your EGR... that might be triggering your cat code too.

[chuckthefuk]

In some cases Sea-foam can damage the diaphragm inside the BPT /EGR.

Simple version:

1. Disconnect the vacuum source to the EGR valve.
2. Start the engine and idle.
3. With a vacuum pump, apply vacuum to the EGR valve.
4. If vacuum does not hold, the diaphragm is ruptured. Replace the EGR valve and gasket.
5. If the engine did not stall, the EGR passage is clogged or the EGR valve is bad.
6. Remove the EGR valve and repeat step #3. If the valve does not open, replace the valve.
7. If the valve opens confirm that air flows through the valve. If air flows through the valve, the passage or EGR delivery tube is clogged.
8. Apply air pressure to the opening of the EGR delivery tube and confirm that air passes through it.
9. Apply air to the collector passages and confirm that air passes.

If the tubes are clogged try to remove the tubes and cleaning them so they are not clogged. Soaking the tube with a solvent thats safe for rubber and blowing through with an air line or compressed air can to confirm its clean and free of obstructions.

-Chuck

[Wiscon_Mark]

An 8 mile drive means you're not really warmed up and are running a high percentage of your driving time in a "cold" fuel map, which means the ECU dumps a large amount of fuel to keep a safe A/F ratio. When you drive highway, I'm guessing you're going a lot further, so a much smaller portion of your driving is done in that inefficient mode.

Still, 16MPG seems low, I get about 18-20 in the city (winter time, summer is more like 22) driving about 5 miles to work. Work out those codes, clean everything out, and then measure your economy on the next 3 tanks and see how things go.

[geckoboy86]

An 8 mile drive means you're not really warmed up and are running a high percentage of your driving time in a "cold" fuel map, which means the ECU dumps a large amount of fuel to keep a safe A/F ratio. When you drive highway, I'm guessing you're going a lot further, so a much smaller portion of your driving is done in that inefficient mode.

Still, 16MPG seems low, I get about 18-20 in the city (winter time, summer is more like 22) driving about 5 miles to work. Work out those codes, clean everything out, and then measure your economy on the next 3 tanks and see how things go.

I get that mileage year round.

This issue isn't new for me. Just with rising gas prices, its moved up on my list of getting stuff fixed.