Mercruiser 350 mag mpi losing fuel after 30 seconds

briwilde

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Jun 25, 2022
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2
We have a ski centurion 03 escalade v drive boat. I took it out this week to make sure it was working for our family reunion trip. The first day was great, no issues. On day two, first thing in the morning the issue started. It idles fine and when you push down the throttle it runs great for 30 seconds then sputters and looses power like its running out of fuel. When I pull back throttle and let it idle it runs fine and then will run for another 30 seconds with the throttle down until it sputters again. It consistently will run for 30 second spurts between idling sessions. It seems that its consuming all the fuel it has in the system then abruptly runs out. Has anyone run into this issue? I'm assuming its the high pressure fuel pump, but its in a hard place to reach with this boat's engine compartment. Would a clogged fuel filter or water fuel separator cause this or would the problem show more gradually? Maybe a bad antisyphon valve? Please help
 

ScottinAZ

Master Chief Petty Officer
Joined
Jun 25, 2009
Messages
861
check your tank vent......

loosen the fuel cap a bit and make a run (carefully), see if anything changes.
 

briwilde

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Jun 25, 2022
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2
check your tank vent......

loosen the fuel cap a bit and make a run (carefully), see if anything changes.
I actually tried that. I loosened it and some air sucked in. It didn't change anything, but I didn't run it with the cap loose, I just let the pressure equilibtate and then retightened. Should there be any kind of pressure buildup at all? It seems like there is always some air moving in or out when the cap comes off.
 

ScottinAZ

Master Chief Petty Officer
Joined
Jun 25, 2009
Messages
861
there should not be any air movement when the cap is removed. If you are getting an air inflow, the vent is plugged, and your tank is running into a vacuum situation cutting off fuel flow.

Once you screwed the cap back down, it resealed the tank, and the situation could repeat.
 

alldodge

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Mar 8, 2009
Messages
42,881
With it just taking 30 seconds I would suspect somethings clogged or fuel pump. Check fuel pressure at the rail

Pull the fuel filter and dump contents into something clear so you can see if there is nothing but clean gas. When removing the filter note if its full of gas or a bit below full

If bit below check antisiphon valve at the tank.
 
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