Low MPGs, no obvious reason.

[Eddie25]

Originally Posted by Old Mechanic

02 sensor getting tired?

regards
mech

how would the O2 sensor effect FE? my engine light has been on for a while now needing the left bank o2 to be changed however I am still getting very good millage so im not in too much of a rush to replace it

[spacemanspif]

Originally Posted by 2000mc

jinx

Lol

Originally Posted by Eddie25

how would the O2 sensor effect FE? my engine light has been on for a while now needing the left bank o2 to be changed however I am still getting very good millage so im not in too much of a rush to replace it

The primary O2 controls A/F ratios, the secondary just measures catalytic converter efficiency on most cars. Your check engine light is probably just the "cat inefficiency" code telling you the sensor or the cat is not up to par. Either way it won't effect the way the engine runs. Front O2 would probably only cause a rich or lean cod which would impact FE. .

[darcane]

Originally Posted by 2000mc

do you know what your fuel trims are running?
When you fillup, does your gauge agree with the actual fill as well as it did previously?

Ran in this morning with long term fuel trim gauge active. The gauge reports percentages from -100% to 99.2%, my car was at 1.5-2.3%.

[darcane]

Originally Posted by spacemanspif

I had a wandering idle in my Saturn but it was "searching" any time it was idling in closed loop, turned out to be the fuel pressure regulator was leaking gas into the vacuum line. If your gas pedal feels a little sticky your TB could be dirty, which could also mean your IAC could need cleaning like KSA said.

Could be a lot of things, what is status of tune up stuff? Plugs, fuel filter, etc.

Plugs were done a couple years ago and looked fine when I had the head off, fuel filter is inside the tank so I haven't replaced it.

[darcane]

Originally Posted by 2000mc

do you have a vacuum modulated fuel pressure regulator? leaking regulator would explain poor actual mileage, while electronics report best ever

Electronics are reporting crappy mileage though....

I can keep the mpgs high on the freeway (I P&G between 50-65mph as long as traffic allows) , but when I get on side streets it plummets. My last tank was 39.2mpg per the pump and odometer; the Ultragauge reported 38.9mpg for the tank.