04 chevy impala Horrible gas mileage! P0420 p0455

Question

My check engine lightgot came on about a week ago, so I went to auto zone to have the codes scanned and diagnosed. Two codes came up, p0420 for the catalytic converter, and p0455 for a gross leak in the evap system. Now I'm that knowledgeable when it comes to cars but I'd say I kno a lil more than the average female driver. I been noticing my gas gauge is going up and down (slightly, it goes down and then back up to where it was) but I'm getting maybe 10-15 miles a gallon. I also feel it doesn't accelerate as fast as it should, nothing very significant tho. I've talked to many mechanics and they say a code for the evap system wouldn't affect gas millage, but I feel like it would considering it has to do with lines to the fuel tank. I've also been told to try a new gas cap first, as that might be the problem. I've already made an appt to fix the catalytic converter, but what I really want to know is which code is the reason for my poor gas mileage?? I would just like some advice before I spend the money to fix anything. It's very frustrating, I've been spending too much money on gas that's barely getting me anywhere!

Answer 1

The fuel gauge may not be accurate , If the vehicle does not feel as it accelerate as it should this is where a tune should be inspected for especially if the catalytic convertor is being replaced, it is not a good practice to replace the catalytic without checking the cause if any.

Check for needed tune up , worn sparkplug such as this rob the engine of power