Fuel pressure measurement after trying different pumps

[craigify]

I have a question about measuring fuel pressure on a GM TBI setup. I've just built a 468 (454 bored 0.060 over) in my school bus RV conversion designed for torque. I've put in a Delco EP377 pump which, according to them, has a max pressure of 60psi (I assume deadheaded) and is usually used to run 30psi 94-95 injectors. I see people talking about these all the time.

Anyway, when I measure fuel pressure on the line from the pump to the engine, I only get somewhere around 10psi. I'm running aftermarket injectors from an earlier set up and not the smaller 30/40 lb injectors on the 94-95, so this 10psi is kind of low factory spec. However, I assumed I would see 30psi on the fuel line when measuring. I had another 30psi pump that I tested, and I got a similar result...about 11psi on the tool. I tested two separate measuring tools thinking one was broken. Same result on each.

I assumed that the pump would pressurize the supply line similar to 30psi, BUT I'm now realizing that maybe the spring in the pressure regulator assembly on the TBI unit would influence the reading. I thought that the pressure behind the spring in the line would be directly influenced by the pump. Can somebody confirm that my 10-11psi reading when taken on the supply line is directly due to the current spring? Therefore, if I switch to a 15psi spring, I'd see 15psi there?

I've taken measurements immediately after the fuel filter and right before the TBI unit itself. Same reading.

[steveo]

assuming no restrictions or clogs your fuel pressure measured anywhere before your regulator will be regulated by the regulator

its possible to get a pump much larger than original and outflow the regulator, and see additional pressure that way. but thats usually a bad sign

[steveo]

to give you an idea how it works, your pump doesn't create pressure, it just moves the fluid. to create pressure in a pipe you need to restrict the flow. so the regulator creates a restriction until pressure in the pipe builds, then the valve opens and lets excess pressure down the return line
if the regulator was stuck closed you would see the maximum pressure the pump was capable of sustaining
if it was stuck open pressure would be approximately zero

[craigify]

to give you an idea how it works, your pump doesn't create pressure, it just moves the fluid. to create pressure in a pipe you need to restrict the flow. so the regulator creates a restriction until pressure in the pipe builds, then the valve opens and lets excess pressure down the return line
if the regulator was stuck closed you would see the maximum pressure the pump was capable of sustaining
if it was stuck open pressure would be approximately zero

Thanks, Steve. This seems obvious now that you've typed it out. Much like oil pressure!