07 5.9 When I'm driving 70 miles an hour on flat ground my boost is 12 psi What could cause this I've checked for boost leaks I change the wastegate actuator Because it had a busted Diaphragm the map Checks fine From what I can see
The reason I ask because I'm getting about 12 mpg The truck is bone stock besides 60h II injectors

 

just put in injectors? no tuner or anything like that? are you always blowing black smoke?

 

Need a tuner! Smarty is easy!

 

You should not be seeing that much boost on flat level ground at a constant speed. Have you checked for codes?

Have you tried another boost gauge to rule out a faulty boost gauge? Is your mileage hand calculated?

 

why shouldnt you be seeing that at a constant speed and ground? my truck stays around 10psi at 70MPH on level road....

 

IMO that is a lot of boost for minimal engine load.

At 70 mph on flat level ground I run 3-5 lbs of boost, and my mileage is close to 20.

 

I was thinking that was high, too. At that speed and situation, mine is about 3-5, also, with 17-19 MPG at that speed.

 

What RPM are you turning?
Auto or stick?
Gear ratio?
Park brake off?
Seriously that is high but it just may be your gauge is off try another one! Your mileage sucks so there may be other issues like a melted piston or bad injector causing the engine to work harder on 5 cylinders. These engines are great at hiding problems by compensating fuel to the other injectors to keep it running. Seen it alot bad mileage is the only real give away something is wrong!

 

mine is 6 psi driving at about 70 on the highway, but your trucks are a lot newer and shinier than mine, but one time i was chaning my oil filter on my truck and smashed the line for the wastegate, she ran 15psi at about 60 mph and i didnt notice the smoke til the cops came flying

 

I'm turning about 2150 at 70 It's a stick and had 373 Gears Breaks are all good nothing sticking If I had a Melted piston Wouldn't the truck run batter or use oil Or have some blow by