Legacy Fuel economy

[Florian Feuser /FFF/]

My 96 Legacy GT (2.5l) is getting relatively poor fuel mileage (aprox 20Mph in
50/50 city and highway).

It did throw a CEL a while ago but it hasn't come back after the codes were
cleared due to a battery replacement.

I suspect the O2 sensors being old and "lazy" and needing replacement.

Is there a reference for average or out-of spec values of O2 sensors? E.g.: rich-
lean switch times, low and high voltage etc. etc.

florian

 

[David]

My 96 Legacy GT (2.5l) is getting relatively poor fuel mileage (aprox 20Mph in
50/50 city and highway).

It did throw a CEL a while ago but it hasn't come back after the codes were
cleared due to a battery replacement.

Some trouble codes don't trigger the CEL. You could do a code scan and see
what comes up.

I suspect the O2 sensors being old and "lazy" and needing replacement.

If they're old, might as well replace 'em. Might not hurt to see what the trouble codes
are first though. Wouldn't want it to be something that would foul the new O2 sensors.

 

[Florian Feuser /FFF/]

Some trouble codes don't trigger the CEL. You could do a code scan and see
what comes up.

No codes are stored - that's the problem.

If they're old, might as well replace 'em. Might not hurt to see what the
trouble codes are first though. Wouldn't want it to be something that would
foul the new O2 sensors.

I don't really know how old they are. I bought the car at 140k miles. I'd like
to compare their output to what typically is within spec before throwing out a
pair of perfectly good O2 Sensors.

What else causes a significant hit in fuel efficiency (can't be my right foot
alone, I got 26Mpg out of my 2.2l Legacy before)?

Florian

 

[TG]

I have 2.5 and 2.2 Legacys and your fuel economy seems about right to me. I
averaged 26MPG from all of my 2.2s but my one ton truck can beat the 2.5s at
times...I wish I didn't have the 2.5 for a number of reasons. TG

 

[tcassette]

For winter blends of fuel and temperatures, your mileage is close to my 96
Outback 2.5l. If you are in California, there might be other issues (like
the emissions control system). The best I have ever gotten in warm weather
at constant highway speed is about 28. In winter (Nebraska) I average about
21 mpg per tank at 80% highway driving. In what's left of the year, I get
about 24 mpg per tank.

 

[Florian Feuser /FFF/]

I have 2.5 and 2.2 Legacys and your fuel economy seems about right to me. I
averaged 26MPG from all of my 2.2s but my one ton truck can beat the 2.5s at
times...I wish I didn't have the 2.5 for a number of reasons. TG

It's definitively downhill from here and worse than I had thought. On of the
last tank fills - after mostly city driving - came to under 17Mpg.

I think the car is definitively running too rich.

Can someone here tell me what values to expect from a "healthy" O2 system in a
Legacy?

The post-cat sensor indicates a max sensor voltage of 0.000 (?) and a min of 1.
275...
no lean-rich switch time at all among other missing values. The pre-cat sensor
behaves relatively normal oscillating between <0.1V and >0.8V. Could that mean
the cat is cooked?

florian

 

[Carl 1 Lucky Texan]

Could also be Engine Temp Sensor telling the ECU the engine is cold all
the time - different from the temp gauge.

 

[Florian Feuser /FFF/]

Could also be Engine Temp Sensor telling the ECU the engine is cold all
the time - different from the temp gauge.

Good idea - but the OBD II scan tool shows the coolant temp/ relatively steady
at approx/ 185F.

Filled the car up again on Saturday and got 160 miles out of 15 gallons.
Feels like I am driving a Jeep Wrangler

florian

 

[R]

Filled the car up again on Saturday and got 160 miles out of 15 gallons.
Feels like I am driving a Jeep Wrangler

florian

Is gas leaking out somewhere while you drive?

 

[Florian Feuser /FFF/]

Is gas leaking out somewhere while you drive?

Nope, except through the combustion chamber obviously

Seriously, if that were the case I'd expect a strong smell of raw gas from under
the hood after stopping the car. No such thing though.

I'll try new O2 sensors next - I was only hoping someone with an OBD2 scan tool
could share with me his/her readouts from a working emissions control system.

florian

 

[Carl 1 Lucky Texan]

Either something is telling the ECU to richen the mixture or something
(like an injector) is failing to control the fuel. Try looking at the
plugs for one that is different from the others. That cylinder could
have a bad injector I guess. Not sure the 185 you're reading is from the
same sensor the ECU uses for engine temp. On soobs there are 2 different
sensors, near each other, on the coolant xover.
Anyway good luck.

Carl
1 Lucky Texan

 

[Edward Hayes]

I missed the start of this thread but such hi consumption might be that the
computer has shut down to limp-home mode buy, I would have expected CEL.
Other than that, since you say no cods I would suspect an O2 sensor heater
which will not trigger a CEL. O2 sensors were recalled for a free
replacement on my 2000 Forester but I'm not sure which years were included.
Ed Hayes