454 Mag MPI fuel issue
 

Hello all, I am new to this site, so if there is a dup post, I am sorry. I have a 1996 Baja 24 Outlaw with the 385hp 454mag MPI and am having some issues with it dying on me after about an hour of trouble free boating. It has been in the shop since memorial weekend at a pretty reputable service shop and they are at their wits end. They even have the Mercury engineers involved. The problem seems to be with vapor lock or similar. They have replaced: fuel pump, fuel pump regulator, fuel seal kit, diaphram in the VST. It still isn't fixed and my summer is running out on me. If anyone has had or heard of this same problem, I would like some advice or direction as to where to go from here. Thanks in advance!

There is a lot of info on here for vapor lock try doing a search on it you will get a lot of info that might help, You might even want to see if the service guys working on the boat are willing to look over this fourm to see if they can find anything they have not tryd yet.:party-smiley-004::drink:http://www.offshoreonly.com/forums/g...ght=vaper+lock Here is a link to get started on, Good luck.

there is a vent diaphram and check valve in the vst tank lid if it is not working right it will not let air out of the vst and will not let fuel in you might want to have that checked.

Welcome BK...

Seems like there is a certain mechanical fuel pump that was prone to vapor locking. Trying to remember who I was talking to about this a while back...

(Im FlyinZX11 on whatsupontheriver)

Ck for erratic map sensor. Have shop hook up Diacom and test on the water. Have fuel pressure hooked up as well. Run it till it dies and verify specs. May be only way to find it. Good luck!

I'm dealing with a similar issue like this as well on a 98 7.4mpi. After 45 min of run time I lose power bad, the fuel pump is louder than sh!t. If I let it sit for a bit I can run for awhile before it happens again. I have replaced the injectors so far(had 3 that tested bad) and now i'm going to order a new pump and regulators.The injectors helped getting on plane but the 45 min problem is still there. I am really confused on this one. Whats up with the fuel pump whining so loud?

Sounds like the fuel system is getting cloged with something between the bottom of the fuel tank all the way up to the fuel pump. Also could be sucking in air from a broken fuel tank pick up tube, could be the inside of the fuel hose is braking apart and blocking some of the fuel flow making air bubbles, Could be a bad fuel pump. [ect].

Maybe a fuel tank vent,i have plugged mine after buffing the boat.

I have completely taken apart and cleaned/flushed every line from the tank to the injectors. I sent the injectors out, and 3 were bad so I replaced the whole set. I opened the tank and everything looked fine there, no sediment, water was found. I haven't taken apart the vent/ line to see whats up there yet. I will do that today. I was ready to order up the pump/cooler combo and a map sensor today. I will wait to see if the vent is restricted first. I really hope the vent is clogged.