Dead head ( no regulator or nothing) and only 30 psi sounds like the pump is bad.

So, deadheaded will go 50 or 60+ psi?

Yeh, try a new gauge. Been thru a bunch of those but then again, I use them a ton.

You could definatey have a volume issue, dead heading is not feeding anything but it does tell you what psi it can pump against. Sounds like a feed issue...either mechanical pump, anti-siphon valve, crack in fuel pick up, or air getting in one of the pre-pump fittings.

Something's up in the vs tank. If I tap the tank next to the pump with the handle of a screwdriver the pressure slowly rises and becomes erratic as it was the other day. I need to change the fuel delivery system. I'm not buying an 800$ vst.

I'll sell ya mine for $150 if you want to try another. As before replaced mine and went to cool fuel because I didn't want to have to deal with possible replacement if it ever died

I have some thinking to do. Appreciate the offer, I'll let you know. Thanks.
Doug

Your pump should supply around 42-45 psi to the rails under full load at wide open throttle.
If you are getting less than that under WOT conditions, then you are starving your motor for fuel.

Your regulator is vacuum indexed to REDUCE fuel pressure when the intake is under vacuum, but wide open there will be less than 2" HG of vacuum in the intake (setting the bypass back to 43 psi).

Don't deadhead your pump unless you do it very briefly by restricting the bypass line. But if you do that, it should flash up past 60psi pretty quick.

As far as your complete fuel system, the line FROM the tank (after pickup screen and check ball) should not be under more than 3" vacuum at max fuel flow. With electric pumps, when all pumps are running, you are at max fuel flow so this can be checked without the boat underway. But you can also have junk in the tank that clogs the screen when underway so keep that in mind.

You mentioned a sound like detonation under WOT and then replacing the cap and rotor. What about plug wires. My 502 would get maybe 2 seasons out of a set of wires before they began leaking current and causing high speed misfires (not so much audible, but you could feel the misfire thru your feet if you were standing in the bolsters. The arcing wires also made a muted detonation-like intermittent popping sound. With twin 502's ONE plug wire off lost 50 rpm. One off each motor lost 150 rpm. Two wires off each motor lost 650 rpm.

Don't start beating your head against the wall yet.
Just get the fuel pressure up where it is supposed to be. Keep a pressure gauge after each pump if you have 2. The initial pump should not drop below 4 psi. The high pressure pump (at WOT) should not drop under 41. Until you fix this, do not look elsewhere. Even if there are other gremlins, you NEED proper fuel pressure or you will be risking expensive damage.

Sounds good. Thank you for the reply. Too many issues at one time. Tough to stay focused. Got a leaking drive and a froathy oil fill cap as well. Trying to just get my fuel system sorted before I tackle the other issues. There's a good used engine down the block from my house that's looking mighty tempting. "Carb to pan". Same set up with less then half the hours I have. But that's a gamble as well. I've only dead headed the pump very quickly. It hasn't been simple to test the low pressure side, but I need to do that next.

Well, after all is said and done. I have a fuel system working at 30 psi consistently . Next step is to borrow a local aquaintance's vst and see if that changes anything. If 30 psi was spec, and I had 4600rpm. There would be no symptom.

New reg and pump. Validated b+ at pump and good ground. I can dead head pump for a split second and pressure rises very quickly.

Injectors serviced.

Boat runs great. No misfire. Starts immediately ever time with authority.

Only thing I haven't done is validate my fuel pressure with another gauge.