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.