So I had a question about fuel pressure. 2006 Sierra that I upgraded to a Walbro 255 (gss340). Started having some starting issues, cold start would be funny, and hot starts would have to cycle the key twice to start decent. So I put a fuel pressure gauge on it today, and as I expected, it will not even hold pressure during the prime. Jumps to 58/60psi, and bleeds off almost instantly. So I know there's an issue there. With the engine running, it holds a steady 58/60psi, but at WOT is drops a couple psi to about 54ish. Is the wot fuel pressure normal? I assumed at wot is would increase in pressure not decrease. Or maybe I'm wrong. Anyway, I know I need to pull the pump and see why it's bleeding off, but just wondering if the wot pressure is right? Thanks guys

 

The returnless systems tend to decrease pressure at heavy throttle... its far from ideal.

As far as the start up issues it seems to point to a regulator problem I would think but I cant say for sure.