940 Turbo Gas Mileage - Air Cleaner Case

I wrote several months ago about the miserable gas mileage I get from my
1994 940T (automatic) Wagon. I still get about 14-16 Miles per Gallon in
the city and up to 22 MPG on the highway. This is far below expectations,
and feedback from the group suggested that something was amiss - probably
vacuum or turbo hose. The Volvo specialist that has worked on the car for
years shrugged his shoulders and told me that "it is what it is - There are
no adjustments - If there was a vacuum leak, the CHECK ENGINE light would be
on.

The Volvo dealer told me to go find the highest price premium gasoline I
could buy and use it. Premium gas did get me about 2 MPG, but it still
seemed way too low.

Tonight I discovered that the plastic case that holds the air filter has not
been properly closing. A previous owner (or mechanic) had broken off the
clamps that hold the two pieces together. Instead of the clamps, sheet
metal screws were used to hold the two pieces together at the four corners.
One of the screws had stripped out of the plastic below, and the tension
from the air filter gasket had opened a seam between the two pieces letting
in large volumes of outside air.

My new theory is that this outside air is not welcome, and that the O2
sensor is getting a false reading - telling the fuel injection system to
keep adding gas to the "lean" air mixture it sees created by the breach.

I have re-sealed the box (using a new screw) and will now run a tank of gas
through to see if there is an appreciable difference.

Am I dreaming or does this make sense?

Dave in Oregon

 

The airflow sensor is after the airbox so the leak shouldn't effect fuel
economy, it's certainly not good for the engine to be breathing in all that
unfiltered air though.

How's the tire pressure? That can make a big difference, it's also worth
checking the plugs, cap, rotor, wires, and timing. I would expect closer to
25 mpg on the highway, I find the best fuel economy comes with midgrade
fuel, premium gives just a tad more pep in hot weather but slightly lower
economy.

 

Just got it back from my regular mechanic. He agrees with the other
mechanics: It is what it is. Having checked out the vacuum lines, O2
sesnor, and computer diagnostics, he could offer no further help.


Too bad! I thought I had a nice car that could be the family campmobile and
get decent gas mileage. It just seems odd that a four cyl 2 litre automobile
uses 40% more gas than a full-sized chrysler minivan with a 3.3 litre engine
(I used to get 28 mpg at 80 miles per hour in the old Grand Caravan that I
replaced). To me, however, if the Volvo wagon gets the same mileage as a
HUMVEE, I may as well have the room. I didn't buy it for speed, but I guess
that is how it was optimized at design.

I am terribly dissapointed. I am just happy that I didn't invest $35K for a
new one.

THIS PIG IS FOR SALE!

Dave

This car is going on the market