Hello,
Can't figure out why i only make 15mpg (combined
already did the usual:
changed oil, new plugs, new air filter, rebuilt tranny, fuel filter still good, O2 sensor still good, factory psi on tires, new suspension and newly aligned , new TBelt, seldom use AC since onset of cooler weather. Spark plug wires, rotors and caps looks ok. Are there symptoms of bad wires, O2 sensors or fuel filter? Car runs strong but gas mileage sucks! Should i change the O2 sensors, high tension wires and fuel filter?
thanks for any inputs ..
Tobin

94 850 wagon, auto, 185K, non turbo.
location - LA,Cal

A failing O2 sensor is a good bet. Also, a failed ECT sensor will make the engine think it is stone cold all the time. A major vacuum leak will also fool the ECU into enriching the fuel mix thinking the engine is running too lean. Check bay 13.

bl

thanks for the info
so should i replace the front and rear O2 sensors?
thanks again

They're pretty pricey to just replace w/o knowing they're bad. Are you seeing black smoke out the exhaust or smelling a really fumey exhaust?

I forget the exact voltage involved but if you have a digital VOM you can check your O2 sensors to see if they are at least working. You need to first unplug the O2 sensor connectors (a little difficult the first time). Look on volvospeed.com (bay 13) for pics. ALso look at his section on vacuum leaks. The O2 sensor signaL wire is the black one (there will be two whites and a gray also) Set your VOM to the smallest voltage range (1v) and hook your red + lead to the black wire pin in the connector and the VOM black - lead to ground. Start the engine and watch the voltage. A good front sensor will show a voltage range of about .3-.7v I think that will fluxuate constantly and rapidly. A low steady or no voltage on the front = bad. I think the rear one reads something like .25v and is pretty steady. Also, many mechanics have an O2 sensor tester made for that purpose that will tell if they are bad. You can also look over in the 700/900 FAQ on this forum for a lot of info on testing 02 sensors.

Had the same problem w/ my 96 850. Check your fuel pressure regulator, common cause of poor mileage.