1. Home
  2. Volvo automobiles
  3. Air filter and fuel economy

Air filter and fuel economy

I frequently see dirty air filter listed as a major factor (since it is listed in the first few items) in degrading fuel economy. Doesn't this just simply restricted the rate of air input and the ECU would then adjust the fuel flow to suit?

I'm currently looking for the factors that has caused a sudden drop of ~25% (from 6.5km/l to 5km/l) in fuel economy in a 760 V6 and the above assertion puzzles me. In my case, as the oxygen sensor is making enough transitions between high and low value, the fuel mixture is probably ok. In my way of thinking this means the air filter and the air way is no longer a major factor. The poor fuel economy is caused by un-burnable fuel going through the system due to: a) Weak spark; and b) Fuel spray pattern or fuel droplets size. Any idea how to test for these problems?

The other factors I can think of is drag due to things like brakes and fuel leaks, which I have found and corrected. Can anybody add something else?

Reply to
Duong Nguyen
Loading thread data ...

True.

It does several things. One is to reduce the efficiency of exhaust scavenging (and thus economy).

Although European "performance car" nuts in past decades would tweak the air filter as one of the first upgrades, they were often running the sort of long-overlap camshafts that were least sensitive to restricted airflow. Unless they ran their engine completely flat out (which admittedly you had to back in the days of anything over 100HP being a big engine) it didn't really make any difference.

These days, with effective engine management systems, a dirty air filter often shows up first as a dirty exhaust, rather than a loss of economy.

-- Smert' spamionam

Reply to
Andy Dingley

More possibilities:

Colder weather, shorter trips, oil change to a more viscous weight of oil, more headlight and other high electrical draw use (heated seats, electric defrosters, higher blower speeds, etc.).

Reply to
Spanky

A frequently overlooked reason is the engine running colder (not at operating temperature) caused by a faulty engine thermostat. Joe

Reply to
Joe

I would suspect the O2 sensor before anything else. If it is failing (or has failed), the ECU drops into a default over-rich condition which will adversely effect your mileage. If you know that the sensor is good, then grab a can of electrical contact cleaner (Deoxit is an excellent cleaner) and start on the sensor connections under the hood. A faulty coolant temperature sender will keep the ECU from going into closed loop and reading the O2 sensor as well.

Good luck, John

Reply to
Fred Flintstone

Since the V6 is normally aspirated, there's no turbo to help in pulling air through the filter system. I wonder what loss could be laid to what is generally called "pumping loss" of power. I suppose that a bad filter would degrade mileage in a turbo, too, in that it would have to work more of the time.

Just a thought, but with modern engines automatically compensating for just about any/everything, the system response would be to provide added fuel for the added work that air problems require.

bob noble Reno, NV, USA

Reply to
Bob Noble

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.