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Jeff d
04-18-2012, 10:07 PM
I just tore into my fuel module due to my fuel pressure immediately dropping to 0 psi right after the pump primes or the engine is turned off.

Things weren't exactly how I had envisioned them being laid out.

Here's my new understanding of how it works. The fuel pump pumps directly through/into the regulator and into the feed line. Fuel goes to the fuel rail and then back to the tank via the return line which just appears to be an open inlet on the top of the module that dumps right into the tank. Once pressure reaches 40 PSI it starts dumping back out of the regulator through the "coaxial" inlet right back into the tank.

Am I on the right track?

What I don't understand is what's supposed to be holding in that 40 PSI after the pump is primed and stops? It seems like there's just an open loop from the regulator back to the return inlet via the fuel rail. Is there another regulator of sorts on the fuel rail that's supposed to keep that pressure?

I can blow both ways through my regulator and it's pretty much unrestricted. Is this normal?

I cannot blow air/fuel back through my fuel pump even with 40 PSI from my compressor. I have a new fuel pump being delivered tomorrow so I didn't care if I broke it.

CantRepeat
04-18-2012, 10:10 PM
Which boat do you have Jeff?

If JimN sees this post is pretty detailed/knowledgeable with a lot of the systems.

Jeff d
04-18-2012, 10:17 PM
'00 230 VRS w/ LTR. I just looked at the boat some more and am even more confused. In the past everyone on here has refered to that puck on the in tank fuel module as the pressure regulator. Is that correct? There appears to be another regulator under the intake plenum on the engine itself. I can't really get a good picture of it since I can barely see it under there.

j.mccreight@hotmail.com
04-18-2012, 10:25 PM
What year and engine, and yes thats pretty much how the system works, iirc there is no anti drain valve built in these fuel pumps safety issue. and all the fuel will just drain back unlike in your car which will hold psi after it's shut down

from the book...
Fuel Pump Electrical Circuit
When the ignition switch is turned “ON,” the ECM turns the
fuel pump relay “ON” for two seconds causing the fuel pump
to pressurize the MEFI fuel system.
When the ignition switch is turned to the crank position, the
ECM turns the fuel pump relay “ON” causing the fuel pump
to run.
If the ECM does not receive ignition reference pulses (engine
cranking or running), it shuts “OFF” the fuel pump relay,
causing the fuel pump to stop.

j.mccreight@hotmail.com
04-18-2012, 10:26 PM
'00 230 VRS w/ LTR. I just looked at the boat some more and am even more confused. In the past everyone on here has refered to that puck on the in tank fuel module as the pressure regulator. Is that correct? There appears to be another regulator under the intake plenum on the engine itself. I can't really get a good picture of it since I can barely see it under there.

yes the fuel pressure regulator in the one on the plenum of the engine.

Jeff d
04-18-2012, 10:28 PM
What year and engine, and yes thats pretty much how the system works, iirc there is no anti drain valve built in these fuel pumps safety issue. and all the fuel will just drain back unlike in your car which will hold psi after it's shut down
So, what's the point of a prime cycle if it's not going to hold that pressure? It might as well just start the pump when you start cranking if that's the case, right?

Jeff d
04-18-2012, 10:33 PM
This is what the regulator on the fuel rail looks like:
http://info.rockauto.com/getimage/getimage.php?imagekey=47146&imageurl=http%3A//info.rockauto.com/SMP/PR92_PRIMARY.jpg

Not necessarily sure that's the right pressure one or not though.

It's on the engine end of the return line so things are starting to make sense to me now.

So, what's that puck looking thing on the in tank module?

j.mccreight@hotmail.com
04-18-2012, 10:36 PM
I guess they figure 2 seconds is enough time to get fuel from tank to injectors to fire it up. Why do you need a "prime cycle" anyway if its designed to hold psi, just a thought...

j.mccreight@hotmail.com
04-18-2012, 10:45 PM
i think what your seeing is the one way check valve for the return line

whats your initial problem, fuel pressure is as follows idle 36-39, cruise 38-42, WOT 40-45

Jeff d
04-18-2012, 10:48 PM
I guess they figure 2 seconds is enough time to get fuel from tank to injectors to fire it up. Why do you need a "prime cycle" anyway if its designed to hold psi, just a thought...

Yeah, but in my boat's current state if I waited 3-4 seconds then I'd be back to 0 PSI. I think it should hold pressure at least for a few minutes. My truck only dropped from 60 to 50 PSI in the same scenario 10 minutes after the prime cycle.

I don't see where your quote from the manual above says that pressure shouldn't be retained for a period. It just says that the pump primes for 2 seconds.

Thanks,
Jeff

Jeff d
04-18-2012, 10:50 PM
i think what your seeing is the one way check valve for the return line

whats your initial problem, fuel pressure is as follows idle 36-39, cruise 38-42, WOT 40-45


That pic is a fuel pressure regulator from a '93 Camaro Z28 w/ 5.7L.

My fuel pressure is within those specs for idle and prime but I haven't been able to do a WOT test with the gauge yet.

j.mccreight@hotmail.com
04-18-2012, 11:37 PM
]Yeah, but in my boat's current state if I waited 3-4 seconds then I'd be back to 0 PSI. I thi[/COLOR]nk it should hold pressure at least for a few minutes. My truck only dropped from 60 to 50 PSI in the same scenario 10 minutes after the prime cycle.

I don't see where your quote from the manual above says that pressure shouldn't be retained for a period. It just says that the pump primes for 2 seconds.

Thanks,
Jeff

There is a coast guard regulation that states that no inlet fuel line shall have psi while engine is not running as to not rupture and having fuel collect in the bilge or get in the boat. I believe this is why the fuel psi goes down after a few seconds, but there should be enough fuel sitting in the fuel rail to get her fired off.

Jeff d
04-18-2012, 11:47 PM
There is a coast guard regulation that states that no inlet fuel line shall have psi while engine is not running as to not rupture and having fuel collect in the bilge or get in the boat. I believe this is why the fuel psi goes down after a few seconds, but there should be enough fuel sitting in the fuel rail to get her fired off.

Ok, so it sounds like I may be chasing after a problem that isn't really a problem. Not to say that I don't believe you but can anyone else confirm that the fuel system is designed so that there should be no residual pressure in the fuel system as soon as the fuel pump stops running (i.e. NOT like a typical automotive fuel system)?

Thanks,
Jeff