So, earlier I drove my car. I didn't notice that I was at 1/8th of a tank of fuel until a mile away from home. The only way I noticed was through my narrow band. (I understand that narrow bands aren't a completely reliable source for AFR's.) The narrow band went from 14.1 to 20 and stuck there, until I slowed down. This was on some hills... My question is; If the fuel was low and sloshing around in the tank, possibly not being sucked through the sock filter, would this cause this sort of AFR reading? I drove home immediately. I plan to get gas tomorrow and check this for sure.

 

Did the car run differently? An actual afr of 20 would barely run. You shouldn't run your car with less than 1/4 of a tank, being submerged helps the pump stay cool and prolong it's life.

 

I really should have checked the gauge before I even left my house. The car didn't run differently at all when I saw the 20.0 AFR. I'm hoping it was just the lack of fuel, and/or an AFR misreading by the narrow band.

 

Its more likely that your O2 sensor is taking a **** than anything else. As stated, your car wouldn't run@ 20 afr, (that's the type of reading you see coasting w/your foot off the gas). Plus most narrowbands don't even read that lean anyway.

 

****... What is the life expectancy for O2 sensors on RX-7's? It seems like people go through them like crazy.

 

With a stock gas tank a very low fuel level can definitely cause a lean mixture due to fuel pressure loss. I've had it happen to me many times. However normally that's under WOT operation on a modified boosted engine, because the torque makes the fuel slosh in the tank.

At low loads I suppose it could happen but it seems much less likely. A stock o2 sensor is a simple 1 wire unit that you can get at Autozone for $30.