2010 Cascadia, DD15, Hard Morning Start

do you have davco filter ?
most likely gallery bypass valve in fuel filter housing is leaking.
take a look here ---> losing fuel pressure on my 2011 DD15 Cascadia

 

I saw a fuel system diagram on one of the posts on this sight. But I haven’t been able to find it. I do remember, there is more than just A check valve that could be causeing your issue.

But when I’ve encountered this issue on DD15’s it’s always been the drain back plug O-rings on the fuel filters. Basicly the test for this is, “did it start at a Fuel Filter Replacement?”

 

Normally with the 2 filter system we find the coalescence filter ( the big one on the side of the motor) has a finger that sticks out the bottom with a o-ring on it. Usually it’s cut. Just remove the filter, replace the O-ring, lube it with an extra slick compound. Vaseline may work, but the filter kits come with a extra slick lube that does a better job.

If you have the 3 filter system (older models) the I believe the button is in the bottom side. It’s been a couple years since I’ve looked at one so I’m alittle foggy on them.

And I’m I haven’t seen the DAVCO filter set ups. So I won’t be much help there.