I have a 2001 Nissan Xterra 3.3L V6 Naturally Asparated that I am wanting to try and make more fuel efficient(although it is a SUV).
Here's what I have done so far:
Ordered 2 new NGK O2 sensors for front O2s
Gutted front Catalytic converters(I have 4 total)
Ordered 2 O2 similators for the rear O2 sensors
Ordered 6 NGK Iridium spark plugs
Replaced both Exhaust manifolds(both were cracked)
Ordered Wix Fuel Filter
Has K&N flat air filter(debating on swapping to K&N CAI)
Ordered NGK spark plug wires
Removed basket off of rack
Removed front cover off of rack
Thinking of doing:
Ordering High Air Flow Magnaflow Catalytic converters for the rear 2
K&N CAI(eliminates all resonators on current air in-take)
Have you been keeping records of your fuel economy? You might want to enter your vehicle into the Garage here and keep a gas log. It will help you keep track of what works and what doesn't.
Your intake and exhaust modifications won't help your fuel economy unless you are running high RPM wide throttle all the time. Any other time, your throttle or your engine speed reduce the demand for air movement so much that the stock system will provide no more restriction than the modified system.
The rack parts that you removed may or may not help. If you want, you can try A-B-A testing to see. Removing the rack entirely would almost definitely help.
Have you experimented with tire inflation pressure at all? That's an easy, free modification that often produces measurable improvements and may improve handling and tire wear. Do not exceed the maximum marked on the tires, and do not go below the recommendation labeled on the vehicle.
Usually the most effective modification by far is to modify your driving. There are many techniques and strategies that you can use that will make a much larger difference than any vehicle modifications.
Well I found that on SUVs and really heavy cars, tire pressure can be immensely helpful to improving fuel economy assuming you take advantage of the difference between doorjamb psi and sidewall PSI difference. In the case of my truck, it made coasting through parking lots without using the accelerator a breeze. Going back to lower pressure made the car feel like it was driving through molasses.