Fueling & Injection - Pressurizing fuel system with scan tool?

I am trying to diagnose a low fuel pressure problem using the procedures in the GM service manual. I am at the step where it says "Pressurize the fuel system using a scan tool." You then gradually close off a valve in the fuel return line to see if the pressure goes up to where it should be (55-60).

Since I don't have a scan tool, would I get an accurate reading by simply running the engine? It seems to me that the manner in which you pressurize the system wouldn't matter. Yes? No?

Thanks,
Ed

Put the gauge on the port, start it. What you get, is the system psi as it actually is. [Assuming it's an LS based engine, it should be in the mid/hi 50psi. Rated psi is 58]
You may want to put the gauge up on the windshield, drive the vehicle, and see if there's a loss of psi under load....

Put the gauge on the port, start it. What you get, is the system psi as it actually is. [Assuming it's an LS based engine, it should be in the mid/hi 50psi. Rated psi is 58]
You may want to put the gauge up on the windshield, drive the vehicle, and see if there's a loss of psi under load....

It is an LS1 in a 1999 Z28. I had already put a gauge on the port and it read 23 (instead of 58) with either the engine running or during the 2 seconds that the pump runs when you first turn the key to the on position. It also does not hold pressure once the fuel pump turns off. I first checked for leaks and injector problems and there were none.

Therefore, the problem must be either the regulator or pump which is where I am now. To determine which of the two is the problem, the GM service manual calls for inserting a cutoff valve in the return line. You than gradually close the valve. If the pressure gets up to ~58, the regulator is bad but the pump is OK. If the pressure does NOT rise all the way, then the pump is bad.

I like your idea of how to perform a load test but my gauge's hose is not long enough.

Thanks.