Sudden drop in milage

[Clay Henry]

All i did differently lately is changed my oil and thats about when i noticed the drop. Was getting 20-21 highway at 65 mph now 16-17 @65 mph.
What else might cause this? Could it be ther oil? I know before i changed it, it had motorcraft oil in it and this time i used Rotella. Maybe i need to get some more Motorcraft?

[Dirk]

Wouldn't be the oil. Checked all of your filters?

[Justinlw]

My current problem started there. Had a bad injector the first time and fixed it then all was fine. Later had an even bigger mileage drop, and the found that the VGT was stuck. Removed the turbo and cleaned it and the mileage came back to even higher numbers than I had before. Mileage dropped again, 2 more injectors gone. Looked a little deeper into the issue and found only 42 psi at idle from the factory pump. I'm in the process of replacing the pump and injectors with a raptor and some 150cc's, and hopefully I'll have enough cash to do a non-VGT turbo at the same time.

[Clay Henry]

Originally Posted by Dirk

Wouldn't be the oil. Checked all of your filters?

Fuel pressure at the heads is a solid 55-60 psi so i assume the filters aare okay since i am reading pressure post filter.

Originally Posted by Justinlw

My current problem started there. Had a bad injector the first time and fixed it then all was fine. Later had an even bigger mileage drop, and the found that the VGT was stuck. Removed the turbo and cleaned it and the mileage came back to even higher numbers than I had before. Mileage dropped again, 2 more injectors gone. Looked a little deeper into the issue and found only 42 psi at idle from the factory pump. I'm in the process of replacing the pump and injectors with a raptor and some 150cc's, and hopefully I'll have enough cash to do a non-VGT turbo at the same time.

I was worried an injector went down actually...how can i tell which one if any? Its not running poory though and no codes.

[TXbroker]

My mileage really dropped before my FICM went out. From 20-21 to 14-15

[Dirk]

Originally Posted by TXbroker

My mileage really dropped before my FICM went out. From 20-21 to 14-15

You also couldn't hardly start the truck.

[TwinTurboStroker]

You didn't change anything in your bio blend did you?

[TXbroker]

Originally Posted by Dirk

You also couldn't hardly start the truck.

At the end it was a hard start, however that only happened right before she went. Now my mileage is back where it should have been.

[Clay Henry]

i don't run a blended fuel, i use straight vegi oil. but no, and diesel fuel gets me the same milage.

[Justinlw]

We run WVO, not bio. I didn't see much of a change in performance when I lost one injector, it didn't go completely. Now when I got it back I noticed it was alot smoother than before.

The dealer called it a "lazy" injector because the spool valve was sticking causing it to shoot more fuel than needed.