why the significant gas mileage difference?

What mileages do they get?

How carefully are you checking your mileage? Have you checked the odometers against each other? (i.e., Are both cars showing the same number of miles for a given identical trip?) The 1996 has slightly higher HP (115 vs 110 for the '94). I assume this is because the 1996 engine is slightly more efficient (higher compression ratio, or less internal friction, or more efficient intake tract). I doubt the difference is worth 4 mpg, but it might be worth some improvement. Have you weighed the cars? The 1996 actually has about 7% greater frontal area, so unless it has much more aerodynamic shape, there is likely to be little difference in fuel economy do to aerodynamic drag. The "combined" EPA estimated mileage for the 1994 was 26 mpg. For the

1996 it was 28 mpg. So I would expect the 1996 to get slightly better mileage. Given the normal variation in vehicles, and mileage estimates, I'd say the variation you are seeing between the two cars is reasonable. The fueleconomy.gov web page also includes MPG estimates from actual drivers. Unfortunately there were not enough people posting for cars like yours to draw any reasonable conclusions (two drivers of 1994 Sentras averaged 30.4 mpg, one driver of a 1996 averaged 38 mpg).

Ed

Yes, the O2 sensor. The main one sticking into the exhaust manifold. Replace it on the 94 motor. O2 sensors can get "tired" without tripping the computer code.

I replace a tired O2 on my 99 Sentra and the car came alive. The car felt more powerful and the gas mileage went up. The original O2 was not pulling any codes.

Also, the coolant temp sensor gets "tired" as well. When its faulty, it keeps teling the computer that the engine is cold when it isn't so the computer keeps running the car rich.

Now, which one to replace? The O2, because the bad CTS symptoms inlclude bad gass mileage AND the car runing a little cool. You would have noticed that your temp gage was sitting a little lower than normal.

CD

Codifus wrote in news:4811f577$0$15157$ snipped-for-privacy@cv.net:

I never heard of a coolant temp sensor getting "tired";all they are is a NTC thermistor,a temp sensitive resistor. I had one go open,on my Integra GS-R.

also,the CTS and the gauge temp sensors are separate items.

Yup, the CTS and temp gage sensor are separate, and the CTS does get tired. Happened in my wife's Altima. Repalcing the CTS shot the car's gas mileage from an abysmall 21 right up to 27 mpg. CTS replacement is slow to adapt, it takes about 3 tankfulls for the ECU to adjust.

CD