Domss2000

i bought a new walbro 255 fuel pump and when i have the rpms steady at any level the psi drops to 35 36 again what can be causing this the car came with a holley fuel regulator also dont know what else to look at.

Injuneer

What is the year, model, engine, tranny and any major mods? If its a 2000, is it a V6 or a V8?

If its an LT1, the fuel pressure will normally sit at 35-38psi at low throttle position. That's the intake manifold vacuum pulling down the rail pressure, using the vacuum compensation line. That keeps the pressure DIFFERENCE between the rails and the intake manifold at 43.5psi. If its an LS1, you're way down on pressure.

Domss2000

its a 96 trans am lt1 lt4 h/c/i 1.6 rockers stall racing trans.

Injuneer

When the engine RPM is "steady", meaning you are just cruising and not opening the throttle, its normal for the fuel pressure to be 35-36psi, if the cam is near stock. At idle, pull the vacuum line off the fuel pressure regulator. Pressure should be between 41-47psi, with 43.5psi the preferred value. Reconnect the vacuum line, and pressure will drop proportional to intake manifold vacuum. A 6-8psi drop would not be unusual with a stockish cam. System should hold at least 40psi pressure with the engine at WOT/max RPM.

Domss2000

alright cool yea when i hold it steady it will drop. ill do that vacuum line unplug to check. so wot it should be at least at 40 ?

Injuneer

At idle, vacuum line off the fuel pressure regulator (and plugged so the car doesn't stall), factory spec is 41-47psi. The "ideal" pressure is 43.5psi, since that's what the injectors are flow rated at.