1997 850 Wagon NA Still getting crappy MPG

[erikv11]

Here's the rear


The front looks similar but is placed before the cat.

[dairyqueen814]

Alright thanks so much
I'll poke around when I get the chance and see what I can find. If my mileage is still in the toilet after this tank I'll pull the front one and see if it's crappy or I might just order new OEM ones anyway to say that I've done it.

[erikv11]

The rear one does essentially nothing regarding AFRs, it will not affect your MPG. Front one matters.

[dairyqueen814]

For anyone who is searching for answers to get better MPG from your Volvo 850 here a a quick summary of this thread:

despite all the things I've already done

(K&N filter, remove pre-heat hose, remove air box thermostat, switch to full synthetic, cleaned PCV system,replaced bad vacuum lines, new fuel filter, cleaned MAF, running mid grade gas, tires are all always at 35 psi, Genuine Volvo plugs and a full stage zero short of a timing belt change.)

My car was still getting around 20 MPG driving mostly highway.
It was discovered after posting here that the engine thermostat was bad so I replaced that (quick ten minute job) and the car appeared to suddenly get better mileage.
After another fill-up though, it seems I'm back to the same old 20 MPG. The next thing on my list is the front O2 sensor and after that I'll just about be out of ideas as much as it kills me to say it.

So if you are searching for reasons YOUR Volvo 850 might be getting bad MPGs try all of the above. I'll be reporting back on my O2 sensor findings as soon as I can.
I also did NOT replace the CTS when I did my thermostat... I will look into that as well but I believe it to be fine.

As always thanks for all the help advice and wisdom so far guys!
~Nick

[dairyqueen814]

On initial inspection and comparison the front O2 sensor is NOT Bosch but looks like a Saab one that some mechanic probably installed.
I'll be ordering a new one from amazon (using the matthews volvo link obviously) and I'll see how it goes.

[dairyqueen814]

Alright guys I'll wrap up this thread
I'm averaging around 25mpg now!
If you stumble across this thread and are trying to diagnose your own MPG problems shoot me a PM because I've seen and tried just about every thing there is in the past 3 or 4 months.

-Nick

[gdog]

DQ814: Don't leave us hanging; so did new O2 sensor fix it?

BTW: Have you changed your oil since replacing the bad therm? If not, do so asap; it's most certainly diluted with gas.

[dairyqueen814]

I still have yet to put the new O2 sensor in. The old one is rusted in there pretty good so I might try heating it up with a torch to get it out. I did change my oil after doing my thermostat. Don't worry I haven't forgotten about you guys I just haven't had a chance to get the part on!

[dairyqueen814]

Real quick for anyone waiting desperately for a close to this matter I just installed my new O2 sensor today and filled the tank.
I'll have numbers for everyone by friday!

[dairyqueen814]

After doing the O2 sensor and seafoaming my intake (whoa baby lots of smoke) my car ran a lot better so what is a man to do but enjoy driving hid beloved Volvo like a race car! so after some red-lining at stop lights and on highway on ramps and cruising at 80-85 I was still averaging between 22-23 this week. After I got it all out of my system (for now) I did a lot of driving this weekend for Easter and just by estimation (like the gas needle still being above the 12 gallon mark and being at 140 miles) I would say the sensor and the seafoam did help. I'm getting at least 25 mpg right now.