Question about fuel pressure test

[tretter7]

Hey all,
I have a 2003 SSV Launch with the 5.7L Indmar engine. This is a TBI motor. When I hook up a fuel pressure to the rail and go to the 'Key On' position it reads 30PSI, but begins falling as soon as the fuel pump stops priming. Falls to about 10PSI and more or less stays there. Is this the correct behavior or is it indicating a problem with the fuel pressure regulator? Or something else? Troubleshooting a few issues with the boat and I want to rule out fuel pump problems before I start checking sensors and whatnot.

Once started and idling the needle stays at 30.


Thanks in advance for any help,
Tim

[2500HD]

The best advice i can give you is to by a clymers manual for your boat. The 29 or so dollars i spent on it saved me more in buying unneeded parts. It will also have the correct fuel pressure spec in it.

[tretter7]

Thanks, I'll grab one. Been meaning to, anywa

[UKandH]

That sounds about right.

Once the ignition is turned off the fuel will *leak back* from an inactive pressure pump as i dont think its fitted with a one way valve. The fuel pressure regulator is there to keep the pressure at 30PSI when running, any excess will leak back to the tank via the bypass regulation circuit.
Some FI systems have a one way valve fitted which prevents this after key off. I always wonder about its value as its not really a requirement.

What are the symptoms ?

[tretter7]

Thanks for the info. I did buy the manual, and while it's VERY useful, it didn't specify about the falling pressure. Makes me think fuel pressure is probably not my problem.

I have two issues going on.
#1, boat is running just a bit rich and a bit rough under heavy load.Fuel pressure is okay, injector spray pattern looks good. Have replaced TPS and MAP sensor.

#2, ECM is putting engine in limp mode at 180F. I suspect the ECT there but am waiting on an IR temp gun to check that sensor. This is tough to duplicate because the boatdoesn't hit 180 often

Any thoughts?

[2500HD]

Have you checked your timing to make sure it is 10 btdc?

[tretter7]

Have you checked your timing to make sure it is 10 btdc?

No, I hadn't even thought to suspect it. I can grab a light and give it a look, can that type of thing known to just go out of adjustment on it's own?

[2500HD]

They won't just got out on their own but if it isn't advancing correctly then it could be kinda rough under load. what kinda distributor do you have?

[CJD]

Could be a bad temp sensor, sending a cold signal to the ECM...The limp mode likely trips once the ECM has enough other inputs to realize the temp sensor is malfunctioning.

[UKandH]

I suspect the same as CJD, that sounds like a temp sender giving the incorrect information to the ECU causing it to over-fuel and stay on a cold start cycle, then when the ECU realizes its at normal expected operation it shuts down on to limp home mode to avoid bore wash and other nasty damage like UHEGO sensors burning out etc.