I have a 2004 350Z with 145,000 miles and a diagnostic shows a code for a bad knock sensor. Can this affect fuel milege? I noticed that when I fill up I have used up 1/4 tank of gas in less than 30 miles and I drive it at 55mpg, if this is the case does anyone know of a reputable place in NJ were I can get it replaced?

 

When knock occurs it retards timing. This is the only way I could see it causing issues with poor fuel economy. If the sensor is dead then it should not emit a signal.

 

If the sensor is dead (or more likely, the sub harness is bad), it will pull timing all the time by default. This is the fail safe for that sensor. I rarely see the actual sensor go bad. It's usually a problem in the sub harness. Replace both to be safe. To do the job right, you need the sensor, sub harness, plenum gaskets and manifold gaskets. I usually do the spark plugs while I'm there.