So i get it, cars (04 tl) getting old and it's not gonna be as efficient as it used to be but I'd say for the past maybe 5 months my mpg has been declining. I used to get an average of 19-20 with my rides and now I'm getting closer to 15-16, is there something that could be going wrong or starting to go out that's causing this or is it just an old car? If it helps, i did my valve cover/spark plug seals & gaskets about 3 months ago, along with my spark plugs. The coils seemed alright so i replace them, but that didn't seem to help my mpg issue. Any advice would be appreciated 👍

 

How many miles are on the car & are the O2 sensors (9;10;11;13 on the link below) original to the car?
Converter - 2004 Acura TL 4 Door BASE (NAVIGATION) KA 5AT (acurapartswarehouse.com)

 

O2 sensors, tire pressure, driving style, driving area/speed, new tires, sticking calipers...I mean all the normal stuff. An insane amount of info on this site from the past 10-15 years regarding low MPG.

 

O2 sensors.

 

The critical data that is needed between your two MPG numbers is the average MPH for the two readings. If the MPH is lower then that can be expected if the MPH is the same then you have an issue. The correlation between average MPH and fuel mileage to these cars is very consistent.

 

did you use the NGK iridiums?

 

Also, how are you determining that MPG number? From the display on the gages?
Or resetting the trip every fill up and dividing the miles by how many gallons it takes to fill?