Had a hard time starting my 1999 502 MAG MPI today. Full throttle cleared it up and off we went. Could smell fuel, but figured it was from the hard start situation. Note that this boat has not given me any hard starting problems ever, but we got caught in the rain today, and I wondered if ignition had got wet..

When we got back to the dock, the boat did not sound right. I can normally here some of the intake vacuum sound at idle, but it got quiet then loud. I opened the hatch, still running and could see fuel pouring out of the vacuum lines that run from the intake to the fuel pressure regulator (cool fuel).

I didn't run it long enough to confirm if it was pushing fuel out of the intake or out of the fuel pressure regulator hose. There is also a Tee there..

Before I dig in too much, does this sound at all familiar? Can a fuel pressure regulator vacuum line purge a lot of fuel? Can the intake push fuel out of it?

We have list some RPMs over the summer, so I suspect this is all related.

If the fuel pressure regulator broke internally, then yes the fuel will be pumped out thru the vacuum lines

I unplugged the Tee from beneath the intake plenum and confirmed that the fuel is flowing from the regulator located below the plenum and not the cool fuel vacuum line. As soon as the key is turned and the fuel pump pressurizes it spews fuel from it.

Would that be a faulty regulator at the fuel rail or leaking injector(s)?

Don't know your serial number, but with cool fuel and the motor is not running but j=key is ON, and fuel is pouring out, then its the regulator on the cool fuel

The Reg on the rail is more a dampner

Just to confirm, fuel is flowing out of the regulator on the fuel rail, and not out of the regulator on the cool fuel. Are you suggesting that the regulator on the cool fuel is overpressurizing the rail and then the regulator on the rail is releasing it?

Thinking it through, if the regulator on the rail is there to hold rail pressure, and its releasing it instead, would it not be the culprit?

dude what are you even talking about, it releases nothing. if you have fuel in the vacuum lines, the regulator is junk, replace it.

LOL I'm trying to learn!!

There's 2 regulators though, and one is puking fuel out the vacuum connection (the one on the fuel rail), so I just want to confirm that's the one to replace before I spend the money. It makes sense to replace that one!

Broken diaphragm = fuel leaky.. got it.

fuel rail regulator,,replace it

One that is leaking is the one that is bad.

It appears that that regulator on the fuel rail operates as a damper. Can it be bypassed or capped off temporarily until a new part arrives?

Could a fairly recent drop of WOT RPM ( about 200-300rpm) have been caused by the regulator failing?

Do I need to remove the upper intake plenum to change it?

Thanks again.