I was looking to see if anyone had a answer to this weird problem! I have a 06 6.0 and I put a blue spring in it. Before I was getting 13.5 mpg for 2-3 weeks after I was getting 16.5 mpg now I’m back down to 13.5 any guesses? I haven’t checked fuel pressure yet and was thinking it was a pump but it wouldn’t go up at all if it was a pump, correct? I’m lost as to why it would go up then back down

 

Curious, did you actually hand fill and check MPG?

Or are you going off the display?

Every 6.0 owner should have a way to check fuel pressure IMO, but at any rate, I would run another tank or two so you have more of a baseline to rule out any calculation mistakes

 

I did it by hand. I filled up last night and got 15.5 so it’s all over the place. My driving hasn’t changed any. I need to do a fuel pressure gauge. That’ll be the next mod for sure!

 

Makes a big difference to me how the truck is leaning at the pump. I get more in when the drivers side is lower.