379 Bad Fuel Mileage

what kinda rpm's are you turning at 65?

 

Download the ECM and see what the lifetime fuel economy is for the truck. That will tell you whether the problem is historic to the truck or with the driver.

 

I drove a pete that was an 06 and it I believe had the MXS engine. It was a company truck and it was also horrible on fuel in the 4 mpg range. Didn't matter what speed you drove it burned it like crazy. The boss took it to cat and they changed the ecm, I think they took heavy haul either out or into it, and the performance went down a little but it brought it up to 5.7. I would not take my truck to cat to have it programmed. Mr. Haney is the top choice. You have something very, very wrong in your ecm to be causing that much fuel to be burned. May also check fuel pressures and restriction and airflow and all that. Aerodynamics have nothing to do with your fuel consumption being that high.

 

I have the same engine that has been tuned I average 5.8 and drive however I please. However, this week I'm down below 5. I'm blaming it on the cold weather while my thermostats are stuck open, making it hard to get my water temp over 140. What are your water temps? Because its under thermostat temp, the ecm tends to throw more fuel in er.

 

well i know there is a guy test the theroy on whats better as far as a turbo wing versus a roof fairing. so far from what i have heard its looking like the turbo wing is better. says the turbo wings surface has less wind resistance still pushes the air about as equal as the roof fairing. he is shock at the amount of wind drag he has found on roof fairings. now he has not finshed testing. he has been test in a wind both so far. watching the wind flows using colored water in the air to see drag and stops and what not.(i am no expert so i dont know what the call all these things.) personally i like the turbo wing. it looks better on a pete than the fairing does.as for the other things that motor has had issues since released. i am sure there are ways to bypass things and get the fuel mileage up. i know that year motor has a major issue with intake actators going bad and when they do the fuel mileage drops bad.

 

How many miles? Could be in need of new fuel lines. Have you checked for any leaks in your CAC and the whole system for the CAC? exhaust leak between the turbos or the manifold? Air filters/ fuel filters?

 

So the truck historically has poor fuel mileage and now you're the proud owner of it. Do you know where the truck came from? If so, any chance you can find out what the previous owner has tried already to remedy this? No point in trying/paying for the same fix over and over again.