Gas Mileage Question

Ok so I recently got my u-bend & resonator removed and ever since that my gas milage dropped from 19-20 (city) to about 16 (city) mpg. I expected it to drop but I didn't know it would drop that much. Also the guy couldn't get my o2 sensor off so I had the choice of getting a new one for $100 or waiting but if I waited he said something like it wouldn't sound good and my gas milage would be shitty. Turns out it's shitty anyway. So what I want to know is that is that much of a drop normal or is something wrong? Thanks in advance.

Are you sure it is not coincidental with the weather change? Normal to see a drop in mileage when it gets cooler due to the longer engine warmup time and time for the PCM module to switch to closed loop mode.

Why did you remove the resonator? A point often overlooked is the engine needs some exhaust back pressure to operate properly and efficiently. I don't recall losing any gas mileage with just a u-bend delete. Don't remember or care on the resonator delete since fuel economy is not a factor for me.

Also, what brand 02 sensor was used?

Are you sure it is not coincidental with the weather change? Normal to see a drop in mileage when it gets cooler due to the longer engine warmup time and time for the PCM module to switch to closed loop mode.

Why did you remove the resonator? A point often overlooked is the engine needs some exhaust back pressure to operate properly and efficiently. I don't recall losing any gas mileage with just a u-bend delete. Don't remember or care on the resonator delete since fuel economy is not a factor for me.

Also, what brand 02 sensor was used?
Oh hmm the weather might be it. Will my mpg go back up once it gets used to the warm weather though? Also I got the resonator removed for a few reasons: mine had a hole in it and he said it would be much cheaper to remove it than to replace it and i was a little short on cash, he said it would give my exhaust a nicer tone (which it definately did), and i've heard about people on here getting it done with no problems so I thought sure why not.

EDIT: And I have no clue what the brand of the o2 sensor was used.

Anyone? I want to know if I have to go back to the exhaust shop (if it is the o2 sensor) and get it fixed cuz this 16 (now actually about 15) mpg just isn't cutting it.

Assuming you're referring to the post CAT convertor O2 sensor since you did a u-bend delete technically that O2 sensor should not affect your gas mileage. All it is supposed to do is monitor CAT convertor efficiency. But in your case if your mileage was normal or acceptable before these exhaust mods then you may have to look into it. With a mileage drop that high obviously something is not right.

A safe thing to do is crawl up under there and make sure they didn't melt any wires welding anything, it's not uncommon.