Would an 05 5.9 have a fuel limiting valve? If so can it be adjusted, tweaked, or modified

 

The pressure relief valve is there for just that. You can plug it off, but if you get too big a spike in rail pressure, it's gonna send it through your injectors, causing them to either crack, or blow the tips off. Either one, and you wind up flooding a cylinder with diesel, then it's a scored cylinder w/ the crankcase full of fuel. Blowed engine comes next.

So yes it can be modded, but without a rail pressure gauge, your taking a $10,000 chance.

 

Wow! Thanks, I didn't know it would be that deep

 

It's to be plugged ONLY when diagnosing a high pressure fuel leak.

I guess while were talking about it, any reason for the interest in modding it?

 

I was just thinking of ways to kick up the fuel flow a bit, I don't want to hurt
anything though

 

You can get a little more flow by getting a little bigger CP3. Something that flows 30% more than stock will be good enough. Not too sure if a CP3 off a 6.7 will work, but if it does, they flow a little more than the 5.9's and be a little cheaper to boot.

 

Doesnt matter if you have more flow or not, if you dont have the programing to demand more fuel.