Fuel pressure loss on LBZ Duramax engine

Looking for some help with my 2006 Chevy Silverado 2500HD Duramax.

When I park it with the front end elevated even just slightly higher than the rear the fuel system loses pressure and I have to pump it up using the manual pump under the hood.
This usually happens after 15 - 20 minutes of park time. When it is parked flat it usually will last hours or more, and if I park it with the rear elevated over the front then it doesn’t seem to have a time frame. in other words it does not lose pressure at all.

Not familiar w/this engine config, but if it is the normal fuel pressure rail and injectors used on most modern gasoline engines, the fuel pressure can leak down one of four ways.

  1. Back into the gas tank due to a faulty fuel pump check valve.
  2. Into the intake manifold due to a leaky injector.
  3. Into the vacuum line of a faulty fuel pressure regulator.
  4. A leak in a gasoline line. Would be visible or at least smellable.

A mechanic could hook up a fuel pressure gauge on the rail and watch how it responds depending on the various up/down parking orientations. Might provide a clue. My first suspect would be number 1, the fuel pump check valve. There may be a way for a mechanic to clamp off a fuel line between the pump and the rail to confirm, if there are any rubber hoses in that path. If the pressure holds when the line I clamped, that would confirm the check valve. Best of luck.

@GeorgeSanJose, the OP talks about it being a Duramax which is a diesel. It will have a transfer low pressure pump to bring fuel to the engine where the diesel pump will take over the high pressure side of things. The manual pump under the hood is there to prime the system in case of fuel filter replacement or other loss of prime.

Like George said, I’d suspect a failing supply pump, but since the problem seems to be related to incline I might also want to take a very close look at all the lines and connections to see if there’s a small leak somewhere allowing air to enter the system.

Thanks you both for suggestions. I will start with the fuel pump (I will go get some type of repair manual to help.)