oxygen sensor + knock sensor change on Infinit I30

[samuelh1]

I have a 1999 Infiniti i30.
Service engine soon light came on and took it to my mechanic. He said that I needed oxygen sensor replaced and my kock sensor replaced. I was also told that my gas mileage will be much better after those changes. Now, it's been about 2 weeks and my gas mileage has been worse than before. I know there is no adjustment to make on Fuel Injection cars. Is this normal? Can it be that the sensors, maybe one of them is bad?
Thanks

[Nahkapohjola]

If your mech is able, the diagnostics will tell if these sensors are faulty with reasonable accuracy. Another opinion/tst at some other shop may confirm that this is even true.... swapping faulty sensors will be in the long run cheapest.

After '100k miles' its typical; free miles dont exist. The KS can be bypassed with 5c resistor, check page 9, clic below. In some engines, KS is hard to reach/swap, mean$$... some shops have special tools to reach em fast and easy, 'cuttin the bill in half'

Jammed/frozen hbrake wires also can make a drastic drop in mpg

[samuelh1]

Thanks Nahkapohjola.
Good info. I just hit 100,000 miles and I know free mileage doesn't come with this kind of mileage. However, I did about 22 - 24 miles a gallon before I changed my Oxygen and knock sensors. Now I started doing about 17 - 18 miles a gallon right after I picked up the car from the garage. I don't think this is normal.
Any how, I know a little bit about cars, so I wasn't afraid to open the hood and make sure that everything was in place. I sealed the air filter perfectly, and pushed on all the other connections (plugs, wires etc...). Now I'm back to 25 miles/gallon again. I would imagine though that if something was loose, the car won't run properly and would have engine light or something. Strange.
Thanks again for your input.

[Nahkapohjola]

Connector oxidation can do just what u explained... signal voltage levels are so low that 'any' dirt degrades sensor signal levels causing ECU to adjust according erroneus input. To stay connected and keep connector resistance minimal, they have to be serviced check http://www.cardomain.com/memberpage/748507/14