Not running and running without vacuum refernce should be the same assuming good state of battery. The only one that should be lower is running with vacuum reference attached.

peace
Hog

 

I didn't prime it with the regulator unplugged.

 

Well put a coolant temp sensor on and that did not fix the issue, I have a MAF on the way that I am gonna try next.

 

Tried another MAF and that did not help. Im about to break down and take it to GM to have them diagnose it i guess.

 

45psi at idle is too low right? Is the new pump an oem pump and did you replace the whole assembly or just the fuel pump?

 

That seemed low to me also. Some people are telling me it is but some are saying for a flex fuel it's ok...? I replaced the whole pump assembly and not just the pump. I bought a good brand pump.

 

Sounds like a weak pump with a faulty check valve thats backflowing into the tank versus keeping the system pressurized. If its nee return it for a new one

 

Well that's what I thought too so I put a new pump in. No difference. I also let it sit over night and checked the fuel pressure with just turned over once and it had instant pressure. You can prime it 10 times if you want but it won't crank unless the gas petal is held down.