Fuel Mileage Issue

I’ve had my Mach for almost a year, and the entire time I’ve had it I noticed the fuel mileage getting worse. As of right now on a fill up I get about 190 miles out of a full tank no matter how I drive it, if I baby it around or drive it like a new rental it doesn’t seem to matter. The car is bone stock 2003 Mach 1 Automatic. Any ideas???


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How many miles on the car.
I bet it could use a tune up.

Oil change with filter
Transmission fluid change with filter
Spark plugs
Fuel filter
Air filter
Clean maf with mass air sensor cleaner , check and clean throttle body
Tire pressure set to 35-38psi when cold

160k I did a full tune up when I got it home, so all that you listed has been done


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Dirty cats.

98 svt said:

Dirty cats.

Click to expand...

I’ve thought about that, have to give it a look


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I really need to check my car out then. I'm getting around 170 a tank.

190 is not bad at all. Assuming you fill up with around 12.5 gallons, and are not running the tank dry, that's 15mpg.

98 svt said:

Dirty cats.

Click to expand...

I agree with this

I have an 03 marauder which is basically the same thing

I get just under 22mpg on the highway at excessive speeds and just over 11 in the city

thats 165 miles to a tank all city filling up 15 gallons
and 340 on long trips refueling 15 gallons on my interstate trips

so i wouldn't say your too far off

I have my marauder detuned to run on 87 octane, she actually gets better mpg's on 87 than 93

First- how are you calculating these mpg's? I would start by filling the tank completely full and resetting the trip. Drive it until the low fuel light comes on. Stop and fill it up and take note of exactly how many gallons it takes to fill the tank completely up again. Then take that number of gallons and your trip mileage and calculate from there. If you already do it this way, disregard.

My eaton swapped Mach goes ~220 miles of 100% city driving before the low fuel light will come on. This always averages between 18-19mpg city. And no, I don't always run my tank that low. Just periodically to monitor.

When mine was running, I was getting about 210-230 miles per tank.