> If I'm understanding you correctly you have a low pressure problem and wanna run the inline along with the current pump to boost your pressure to the normal rate.
Close, but not exactly. The Bonne currently runs except for non-starting at 20F. I was hoping for the scenario in which a new low-cost low pressure inline pump either adds 6-9 psi, or does nothing unless the in-tank pump fails. 6-9 psi might get me started at 20F, and maybe let me limp home when the in-tank pump eventually fails completely. That'* why I asked what the minimum fuel pressure for a smooth idle is.
> 2000 bonneville. It didn't wanna start when it was also below 20 degree'* out. It ran fine under full throttle. But it was also really low on fuel pressure.
Did you get a psi gauge number on that really low fuel pressure?
> Did you change the fuel filter yet?
Yes, my mechanic did that last week in case that was causing the low pressure. It wasn't.
> drop the tank, remove the old fuel pump, and run a piece of hose in place of it and eliminate it completely and then run a high pressure inline pump.
I don't think removing the in-tank pump is necessary, because Walbro http://www.inlinefuelpumps.com
"Walbro inline fuel pumps are ideal fuel pump replacements and upgrades for:
- Vehicles with expensive or hard to replace intank fuel pumps."
This ad implies that OEM in-tank pumps have valves that simply open up when an inline pump is placed in series.
> I understand your management maybe across from you, but they can't evict you or do anything thats done out on the street as thats city.
Alas, their gigantic national corporation no-repair rule also applies to the city street. It'* obey or leave, and I can't afford to leave. (I didn't choose them, the old local owner sold out to them and retired.)
> your in tank pump is making more pressure currently than a low pressure inline would be, so what would happen is that the inline wouldn't do anything at all.
In simple theory it should work, but depending on the pump'* construction you could be right.
Two identical pumps in series should add their pressures the way that two batteries in series add their voltages. But adding a low pressure inline pump in series might not work like high and low voltage batteries in series do. If the low pressure pump has input and output valves, the higher pressure in-tank pump might just hold both low pressure pump valves always open and thus no pressure would be added by the low pressure pump unless the high pressure pump failed (or got as weak as the low pressure pump).
> Fuel pumps actually use gasoline as there lubrication source.
If fuel lubricates the pump body, does it also lubricate the pump'* electric motor bearings? This illustration sort of looks that way: http://www.aa1car.com/library/fuel_pump.htm
I was assuming that the reason for the 20F failure was that the electric motor bearings were running out of lubrication, and what lube remained was too viscous at 20F. But now I'm less certain of that. The only other clue is the somewhat low pressure.
> a round fuel pressure regulator. That regulates the pressure
Ok, I think I get it. The fuel pressure regulator activates the fuel pump relay whenever more pressure is needed in the fuel rail.
Is my fuel pressure regulator bad? I don't know. I assumed that my experienced mechanic attached his pressure gauge directly to the tank line and activated the pump until it maxed out at 29 psi. If so, this test would point to the pump rather than the regulator as the component that was likely to be the cause of a very difficult 20F start. But maybe he just connected to the fuel rail'* Schrader valve and was reading the regulated pressure? I just don't see how regulated pressure that was only 6 psi low would prevent starting only at 20F.