Gas consumption

[shady mousa]

I drive a 2008 Nissan Rogue AWD with 83000 miles on it and my problem started when the gas gauge would give inaccurate readings for example I would fill up the tank and it would show half full it was going up and down whenever I turned on or off the ignition it didn’t bother me much at first because I would use the trip meter to calculate my MPG my car usually used about 21 to 22 MPG that’s city driving I don’t do any highway driving on it, anyways that’s until the gas gauge pretty much went out all together and my dash was showing the gas light telling me the car was low on gas and I needed to refuel, I was told with modern cars with all the computers the car could be tricked into thinking that it was out of gas and all the sudden shut down the engine on me as a safety precautions or something so I went ahead and purchased a fuel pump assembly (Delphi FG1147 - Fuel Pump Module Assembly) and had someone install it for me it was simple as it was under the back seat, he apparently did something wrong because I had the check engine light come on when I checked the codes out it was the fuel pump assembly so a day later the car wouldn’t start and I noticed it was leaking gas everywhere it turns out when he installed the fuel pump he didn’t put the fuel line correctly and the car spelled out all the gas inside of it so after that was taken care of the check engine light still wouldn’t go away even after driving the car for more than a hundred miles, so I was advised to unplug the battery and that should fix it since I already fixed the problem by replacing the fuel pump (I know that was dumb ) anyways the car had just over 83000 miles on it and I thought as a preventive maintenance I should change the spark plugs and ignition coils and while I’m at it the PCV valve it wasn’t expensive and I thought why not that was within a 2 week window from the time I changed the fuel pump, the spark plugs were (NGK 9029 laser iridium) the ignition coils were (QYL) got both from Amazon and the PCV valve from Napa, so after all of that was done we come to the problem a major decrease in fuel consumption I went from 21 to 22 MPG to 16 or 17 MPG I know I did a lot of things that could’ve effected it but I really can’t pinpoint the issue to try fix it I thought spending all that money on the car should make it run better and actually have an increase in MPG but that wasn’t the case.
If it makes a difference I also added a bottle of Amsoil P.I performance improver gas treatment into the gas tank around the same time all of that happened
PS the car isn’t having any problems other than the fuel consumption no loss of power or performance.

[Rogue One]

Did you read the previous discussions on this topic?