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7.4 MPI fuel issuse?

C

Chadepperson99

New member
Hello, got the boat out today, fired right up, let it idle for about 10 min, got the wife and kids on and headed out, idled out of the cove and brought it up to about 2500 rpm, ran for about 5 min the started to fall on its face then died, boat would not restart, so I crank 4 or 5 times nothing, not even trying to start, so I pull the hatch up and start looking at at distributor and wires don't see anything wrong, so I have the wife turn the key, I hear the fuel pump, so don't think there is a issues there, I let it set for a few min and try starting again, nothing, I then turn the key on 5 or 6 times and the the fuel pump kick it's self on then wait for it to shut off, bam fires right up, I turn around to get back home around 3000 rpms and it runs again for a couple of min then starts to fall on its face then dies. I once again open up the hatch, see no leaks, I leave the hatch up, and start cycling the key on and off after about the 3rd or 4th time I can hear a pitch change from the fuel pump, I cycle it a few more times, then try it, bam starts right up, I finally make if into the cove at an idle and to the boat ramp, and just as I get to the ramp, it acts like it's starving for fuel and dies.

I changed the water/fuel separator a couple of weeks ago, so don't think that's the problem, unless it just now sucked some junk out the bottom of the tank, tank was completely full, just filled up today, was also the frist time out this year, I'm leaning towards a fuel pump or regulator issue, anyone have any ideas or other places to start looking, thanks for any and all help.

Boat is a 2000 Mariah 258, with 300 hrs, I have never touched any of the fuel system besides the fuel separator in the 4 years I've owned the boat.
 
Docksidemarineservices said:
This is normal
Click to expand...


Really, i was under the impression, A pump can normally put out 60 psi of pressure and the regulator keeps in lowered between 38 and 43 psi. Mine is either not getting enough pressure from the pump or the regulator is weak.

If the pump is weak and the regulator is OK, then removing the vac line will have no effect.
If the pump is OK and the regulator is weak, then removing the vac line may show some increase

My motor is the 7.4 L29 mercruiser, I maybe back at ground zero
 
What Chris told you is correct.....the pump will deliver whatever pressure its internal valving is set to deliver.... the regulator limits this to the value the injectors and ECU are 'tuned' for....the regulator in your setup appears to be referenced to the intake manifold....so you should see gauge pressure drop once the engine starts up....

If you believe the issue is fuel delivery, you need to measure the fuel pressure and make sure is meets spec across the RPM range, under load.....sometimes, it can be the pump, sometimes the wiring or a connector, and sometimes it can be the ECU control circuitry....a volt meter across the power feed to the pump wires (both) can yield additional info when used with the pressure gauge...
 
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