2000 Civic LX, Auto, 117xxx miles. I have been getting crappy gas mileage (26 vs. normal 32+) and checked the O2 sensor voltage with a voltmeter. Read less than 150 mV. I replaced the sensor only to see the new one give the same readings. The book says it should be around 450-500 mV, never got near that. I assumed a vacuum leak but did not find any, except PCV valve. I saw that PCV was leaking oil at grommet so I replaced grommet and PCV valve and hose. Idled smoother as a result. Voltage gets near 200 mV, but still no where near 450-500. Test was done with it warmed up properly, etc. Would it be a vacuum leak? Exhaust leak? It does sound somewhat like an exhaust leak when it revs up but I'm not positive. Oh, it kinda makes a pinging noise when accelerating up slight grades. I was thinking maybe loose valves for the noise, or incorrect ignition timing. I don't have my timing light or fuel pressure gauge at my current place, but I can check those in the near future. The noise is less pronounced when I use 89 or 91. I'm assuming the pinging and the low O2 voltage are related. Many of you seem quite knowledgable...any ideas? Any similar issues?

 

it could be incorrect timeing, timeing too advanced would cause detonation, and higher octane would help "correct" it. also, be sure that you have your meter on AC voltage, o2 sensors create voltage. and it wont be a very good reading, you should really use a lab scope, which takes a reading over time. and you can really see whats going on.