What happened to my mpg?

Ain't that the truth. But I am a random fueler. Don't like lines. I don't even fill all the way up if I'm not sure the price is right, or just want to be on my way. I did get suspicious. Checked it once. Tried to. MPG seemed down some.

I got some pretty good info on my issue from another site. I will paste it here soon.

 

Ok I suspect you may have a boost leak. To check this look over your pressure lines coming from the turbo to the air to air cooler look for loose clamps or worn silicone boots. Check the lines from the air to air to the engine intake for the same issues. Then if nothing is found there carefully inspect the air to air cooler for cracks the Freightliner coolers where notorious for splitting down the welded seams on the sides if you don't see any cracks then on to the next step. You have two options here the preferred method build two plugs for the tubes going into the charge air cooler on end is a dead plug the other with provisions to couple compressed air into. Pressurize the cooler and have a shut off valve and look for leak down indicating a leak. Or you could spray either around the charge air cooler with the engine at an idle if the idle increases this is an indication of a leak. Or another possibly could be you are in need of an overhead adjustment.