Fuel economy in 2013 F350 6.2 terrible

[treebeardthered]

Hey everyone,

Title says it all.

Have a 2013 F350 XLT 4x4, with the 6.2 and towing package.
315k km, extremely bad fuel economy, the truck says it's average is 23-27L/100km (10-8mpg), but with the power of maths I'm running through about 30L (6 or so gallons) in 80km (50 miles) on the highway.

It really sucks getting 400km (bout 250miles) to a tank on a good day here.
This is not towing at all, 2wd operating.

Few things to note:

Bad -
Cats are low efficiency
Using 275/75/18 Cooper Discoverer Rugged Trek tyres sure doesn't help.

Good -
New Engine Air filter
just cleaned the MAF
All new ignition coils, spark plug wires, spark plugs

Took it to a mechanic for oil change today, they checked the front end to see if there was any resistance causing the economy problems there was not.

They suggested it could be a vacuum leak and to check myself, I have done so with wd40 and soapy water with no success.

Truck's supposed to be 15 on the good end, and 17 on the average end for L/100km, any ideas on what could be the problem?


Another thing to note, before the cats went it was close to the same, best I got was 18L/100km doing 80km an hour on a basically flat road. Moment I had to do any highway driving it was 23L/100km again.
The cats went out because of misfiring due to all my coils were arking when I bought my truck, I have replaced them all since.

Only check engine code is for low efficiency in bank 1 and 2.


Any ideas? The mechanics said to give this a shot if I can't find anyone with similar problems and google searching pulls nothing when it comes to similar predicaments.


Thank you all!

[Flying68]

Run a fuel system treatment.  You may have a stuck injector.  A 6.2 in an F350 is probably good for 18 to 19 L/100km (~12-13 mpg) unladen.  This is based on my experience with a 2019 F250 2WD with the 6.2.

[akirby]

Lazy O2 sensor?