DD15 bad fuel mileage

if he will have high back pressure because of melted dpf core there will be set of fault codes plus 25 or 50% derate

 

It would take me 6 months to log 10hrs of idle time.

 

used one you can find for 5000

 

It's the fuel quantity valve!! It will cost you $650-700 for the new metering valve, but you can change it yourself. There is a video of it on Youtube.

 

That sounds about right for a nearly 10 year-old, 15 litre motor. A 10 speed with 3.36 rears is going to get lower mileage on hills than a 13 speed with 3.55 or higher, regardless of weight.

You are also running at 72 mph. Every mph over 55 mph uses about 1% more fuel (or so the saying goes). So if you ran at 55, you would be getting around 6.5 mpg instead. You are also idling all night, which uses 1-2 gallons per hour (depending on idle speed). Winter fuel blends also burn faster, decreasing economy significantly (1-2 mpg isn't uncommon).

I could pull 6.3 mpg out of a 550 hp CAT C-15 in a 2007 379 short hood (non-aero conventional) running 75,000 gross from Winnipeg to Chicago and back through Wisconsin on summer fuel.

A lot of fuel economy comes from proper specs and driver ability. Think about your idling time, get better fuel, drive slower and keep your cruise time up.

If those things don't fix your fuel usage, it might be an engine or emissions problem.

EDIT: Also, are you doing hard calculations on paper or relying on the truck to tell you what it's economy is? I wouldn't trust an ECM to know how much fuel a truck is using.

 

This is also going on with my 2016 FL Cascadia but I have a code which is always popping up and I’m always taking to the FL shop to fix ONLY for the Yellow light Come on again after driving 100 miles down the road. It shows Air Intake Manifold Derate 25% SPN 102 FMI18
I’m only getting 3mpg. Here’s the kicker. Over a period of driving (a lonnnnng period) The code goes away showing no faults but the yellow light stays on and I’m still getting crappy fuel mileage. No matter how fast I’m going I keep my rpms 1500-1550. Ive lost count how many times it’s been in the shop for this same code. I did replace the DPF. FL said my DPF was clogged 94% but I never had warning light show on my dash. I did it anyway THINKING this was the fix....nope.
I did the Diesel Force Treatment, not sure if you heard about it but it cleans out your whole emissions systems Fuel injectors etc. Buttt guess what same thing, not even a 100 miles down the road and the yellow light came on. I have 498k and have done a lot to the truck already. O-rings replaced before needed. Oil pan gasket and so on. I do idle at night and it wakes me up when the rpms jump from 900 to 1100 for a few minutes but then I have to manually do the regen. This is usually every 7-8 hours during my break but don’t why spend 5k on a used APU if the emissions light keeps coming on, the fault code popping up then going off and then not even 100 miles right out of the shop? I’m one frustrated lady right now and have been since I got this truck for two years this has been going on.
After all that, Do you still think it’s the fuel quantity valve?

 

YES