Getting only 15-16 MPG combined driving...

[jblackburn]

Alright folks,
both O2 sensors were replaced yesterday! I had to remove the turbo inlet tube to get to the connectors. It's too narrow there. Good thing is I had a chance to clean the PTC valve. It wasn't too clogged though.
I was wondering if I should reset the ECU and if there's a special cycle to make it relearn?

Resetting the ECU would be a good idea. Unless you need to pass emissions any time soon, just drive it. The drive cycle is ridiculously complicated, but is here: https://www.matthewsvolvosite.com/drive-cycle.html

[Volvich]

Resetting the ECU would be a good idea. Unless you need to pass emissions any time soon, just drive it. The drive cycle is ridiculously complicated, but is here: https://www.matthewsvolvosite.com/drive-cycle.html

I know, resetting monitors can be a pain. Monitors on mine wouldn't set even after driving for about 300 miles doing different types of cycles. Eventually I had to go to a referee.
Ok, I'll reset the ECU and will get back with milage results.

[Volvich]

My volvich plays games with me
After replacing both O2 sensors and resetting ECU fuel consumption got worse to ~14 MPG!
I don't know what else could be wrong with it.

So far I got:
*New NGK iridium spark plugs
*Bosch oem rotor and cap
*Bosch oem fuel filter
*Mann air filter
*Bosch oem O2 sensors
Turbo has minor internal oil leak, but kicks in just fine after waste gate actuator was replaced by a mechanic. No CEL. Temp guage sits steady at three o'clock position after a couple of minutes of warmup. Engine makes strange whinning almost grinding sound when cold, but once warmed up it goes away. I'll make a video tomorrow and will post it. But for some reason I think its not related to bad milage. Gas milage has been poor since I bought the car two years ago.
I'm running out of ideas...

[whoa]

50-70 mi fwy and 100 mi city a week

That might sound more balanced than it really is. If you're getting, say, 25mpg freeway and 12mpg city, you're using 2 gallons fwy and 8.5 gallons city, for 150mi in 10.5 gallons, or 14.3mpg. That's not great but not necessarily horrible. City mileage depends a whole lot on hills, on how frequently you stop, and on much time you spend at stoplights. In SF I don't think 10mpg is a bad estimate of what I get. I average 23, but only because I put in way more freeway miles than city miles.

Have you measured freeway mileage carefully? Fill up, drive at 65 on a longish, flattish freeway trip, fill back up, and use the amount of gas and a distance estimate from google maps (not your odometer or trip computer).

If that comes out very low (which, my earlier point was, it might not), given all the other stuff you've done you might suspect a restricted catalytic converter.

[TheLoneAviator]

Did this issue EVER get resolved? I've got pretty much the same thing going on. 15.5 avg mpg in town. I'll do the calc this w/e when I fill up to compare.

[E Showell]

Bad engine coolant temperature sensor can cause over enrichment of the mixture and resulting lousy mileage. Could be worth checking.

[TheLoneAviator]

Calc check was 15.0.
Exactly how you check it?

[E Showell]

Generally, I just replace it and the thermostat. The may be a more scientific and less costly way to do it, but I do not know what that is.

[TheLoneAviator]

My STFT S2 is running High ~30, & small evap code. So Im guessing this is why I'm running rich & the poor mileage problem.

[E Showell]

What's STFT S2?