I am a long time Volvo owner, currently own three (an 850 and two S60's). I recently noticed that my 850 qith 120K seems to dropped from about 24 MPG highway to about 15 MPG. I have had the fuel filter, pluds, rotors, wires changed and it seems to run as smooth as it always has. I have also tried premium gas and injector cleaner to no avail. Any ideas?

 

Maybe O2 sensor is going out.

 

I had the sensors replaced about 18 months ago, so I hope not. Also, I checked the codes and nothing showing there.

 

You might want to have someone that can read the sensors in real time check them make sure they are sweeping good.

 

Plugged Catylitic convertor, or A Cat going out?

 

Well, it sounds like you have done most of the tune up items I suggest, but have you changed out the air filter? Also, are you carrying around any extra weight in the trunk? Lastly, check the tire pressure. Even though I don't think low tire pressure could cause a 9MPG drop, I have seen stranger things

 

Some possibilities I can think of at the moment, after a long day:

Engine:
- Retiring PCV system.
- Air induction (Air filter, throttle body, secondary air pump if so equipped).
- Vacuum hose(s) disconnected.
- Faulty thermostat not allowing the engine temp to stay at optimum.
- Blocked exhaust making the engine work harder to counter back-pressure.
- Induction/forced air plumbing leak for the turbocharging if so equipped.
*These may not be present, as your engine seems to be running smooth.

Tranny:
- Check the fluid colour/contamination/level.
- Check that the mode selector is in Economy and not in Sport.

Wheels:
- Check low tyre pressure.
- Check for uneven tread wear/have 4-wheel alignment checked at a reputable shop.

Other:
- A/C beingselected at Defrost, keeping the compressor on at all times.

See attached & wait for more replies.


JPN

[IMG]local://upfiles/6892/AEB3B6728589493FB5E3CC3D8A96A90D.jpg[/IMG]

 

Did the mpg drop all of a sudden or over a period of time? Most of the things mentioned above like tire pressure and air filter is not going to cause a 9 mpg drop.

 

I have replaced the air filter and the tire pressure is fine. Maybe someone is stealing gasoline from it Does anyone know how to check for plugged catalytic converter?

 

You can have the emissions contents tested (CO, HC, NOX, etc...).


JPN

 

I have to agree with tech and JPN. Get your emisions/02 sensors read. I also had a sudden drop and it was the rear 02 sensor and dirty EGR.
Good luck!