379 Bad Fuel Mileage

port and polished manifold gateless turbo turbo blanket open exhasut system ecm tune are things to get the mpg and power up. did you see any codes int act 1,2,3,4,5,6 in the ecm?

 

Check the hoses on top of your fuel tanks that are used to vent the tanks. Sometimes they get plugged with dirt. If you see one plugged up you can wipe off the grime and blow back on the hose to clear it up.

 

You are geared wrong, these motors are designed to "cruise" @ 12-1300 rpm for optimum economy. I've got the same problem,I've got 3.55's now,I have to decide how carried away I'm going to get.I also got over 1,000,000 mi on it gotta decide if I'm going to re-do this one stem to stern or try to find one a little closer to my needs.As far as the fuel level difference goes have the return line "T" valve replaced on top of tailshaft of trans it controls which tank the returned fuel goes to.

 

I have a 34062000 and my best fuel milage is at 1350-1400.

 

Check your air and fuel filters. Make sure you have good fuel and oil pressure. The oil pressure make a big difference in your fuel mpg. And what kind of rear do you have in it? I have 07 435hp acert with 3.42 rear I get best fuel mpg if I stay right under 1300rpm which is 60mph. I had a problem with mine where the cooling fan was staying on all the time it made a difference in my fuel mpg it drop by .5 mpg

 

If that C15 is an ACERT poor fuel mileage is the norm. 4.5 to 4.8 is good for an ACERT.

 

Since when? Been driving a C-15 for over 2 years and I have never been that low.