Hi,
I got a check engine light when my oxygen sensor went out. Changing it improved the mileage, so did changing to 91 octane gas. Fuel injected systems have anti-knock sensors, and low quality fuel will cause the computer to make the fuel mixture rich and/or retard the timing, both will lower the fuel mileage. Perhaps the fuel injector cleaner fools the system to thinking it was higher octane fuel?
Anyway I figure the 91 octane fuel will cost about 5 percent more, but save my by using 10% less gas.
Good luck!
Fred.
PS: THe oxygen sensor is only about $50 and can be installed in your driveway. I used one made for the 96 F-350 with 460" engine, same as my 97 motorhome has. It fits fine, actually there are many vehicles that use that same oxygen sensor. The biggest difference between O2 sensors is the length of the wires and shape of the plug on the end.
Fred.
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