why the significant gas mileage difference?

Do the plugs look different between the two cars? If one is really runner richer the plugs on that one might show more carbon deposits. I presume the thermostat is working well on both and is the same design temperature. Beyond that, if you really want to track it down you can start by putting a scan tool on it and observing the fuel trim and the oxygen sensor behavior. Good luck. Al

What mileages do they get?

thanks al, plugs look identical, temp guage on both are in approximate same position when at operating temp.

what kind of "scan tool" is this that will measure fuel trim and ox sensor operation?

about gas mileage, for 2 years the 94 averages 33.3 mpg and the 96 averages 37.7 mpg; l> >

Seems unlikely but I suppose with virtually everything else being eliminated, you have to consider the odometer calibration may be different. I presume both vehicles use the same type of oil also. Post 1996 vehicles sold in the US must have an OBD-II diagnostic system to monitor pollution related parameters such as fuel trim, sensors etc. When something is out of spec, the check engine light comes on and a code is set. But all of that data is available for viewing with a special purpose piece of diagnostic equipment known as a scan tool that plugs into a data port that all OBD-II equipped cars have just under the dashboard on the driver's side. Pre-1996 cars had OBD-I systems so I'm not sure what diagnostic system you've got on each car. With all the obvious things eliminated, seems like the next way to pursue this is through analyzing the engine data stream. That's a whole other level of complexity. Good luck. Al

no codes are being set, ie, neither check engine light is on.

i am aware of the OBD-I and OBD-II but are you say> >

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

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