CEL & bad O2 sensor, can you have one w/o the other? I am stumped by the working my O2 sensor. The last time I filled the tank I noted a drastic drop if fuel economy. I normally get 35mpg, but this time around I got 24mpg. After searching through old posts it's been well noted that this is a result of a bad O2, but was always preceeded by the CEL. In my case, the CEL does not light up and there is no code when I jump the diagnostic terminal. Is it possible to have a bad O2 and it not post a code or trigger the CEL?
<small>[ September 09, 2004, 07:21 AM: Message edited by: h8ter ]</small>
Sudden Change in Fuel Economy
Re: Sudden Change in Fuel Economy
It is also possible that you got a bad tank of gas, although that doesn't happen too often anymore.
Have you noticed a drop in power? Many things can cause both a loss of power and a drop in milage (AC compressor always on, brakes rubbing, etc.) and then there are things that cause your EFI to dump too much gas in the system (O2 sensor, etc.).
I'm not sure if a bad O2 sensor can cause that radical a drop in mpg without a cel. Someone with more experience will have to answer that.
I would also be skeptical that the O2 sensor went out right with a fill up. First off, they tend to fail more gradually than that, and secondly, if it failed suddenly, it would fail sometime in the middle of a tank of gas, and you would see successive drops in mpg from one tank to the next.
I would suggest you fill up with Chevron, or some other quality gas and recheck your milage before paying for an O2 sensor, unless your O2 sensor is way too old anyway.
It's also possible that something went wrong with a fuel injector. Anything that causes excess gas flow through the system can kill your mpg. After another tank, check the spark plugs to see if one cylinder is running way richer than others.
Sorry if I'm rambling, I'm getting pretty tired. Been working long hours.
Have you noticed a drop in power? Many things can cause both a loss of power and a drop in milage (AC compressor always on, brakes rubbing, etc.) and then there are things that cause your EFI to dump too much gas in the system (O2 sensor, etc.).
I'm not sure if a bad O2 sensor can cause that radical a drop in mpg without a cel. Someone with more experience will have to answer that.
I would also be skeptical that the O2 sensor went out right with a fill up. First off, they tend to fail more gradually than that, and secondly, if it failed suddenly, it would fail sometime in the middle of a tank of gas, and you would see successive drops in mpg from one tank to the next.
I would suggest you fill up with Chevron, or some other quality gas and recheck your milage before paying for an O2 sensor, unless your O2 sensor is way too old anyway.
It's also possible that something went wrong with a fuel injector. Anything that causes excess gas flow through the system can kill your mpg. After another tank, check the spark plugs to see if one cylinder is running way richer than others.
Sorry if I'm rambling, I'm getting pretty tired. Been working long hours.
Re: Sudden Change in Fuel Economy
Thanks for the reply LJ. I was starting to think this topic was taboo or something. To answer your question regarding power drop, No there has not been any loss. I considered the bad gas scenario but I usually fill up at shell and have never had any problems with them. I will definitely run another tank or two through it before replacing the O2. Thanks for the excellent suggestion.