sassea

after fully warming up my 454 mercruiser, i put it in gear and it will move slowly but the moment i start to throttle up,it starts to spit out dark exhaust, bogs down and dies.it once in a while will work itself past this and run normal, but for the most part, it dies out and wont start again..........i also notice a "hissing" noise coming from the engine area but cant find the source, ANY SUGGESTIONS????

Knot 4 Me

Carb or EFI? I would suspect a fuel delivery/pressure problem. Have you changed the fuel filter recently? Do you have access to a gauge to check your fuel pressure?

sassea

its an efi.i did change the fuel filter.........
i dont have access to a pressure gauge...
i do know its "old gas" from 2 seasons ago.its down to 1/4 tank.

murdered6.2

Hissing noise would mostlikely be a vacume leak but that would cause a lean engine unless its a vacume leak to the map sensor which could cause the engine to run rich. Dark or black smoke would be from running rich. Im not sure how the fuel injection system works on your boat, im assuming its a speed density set up and doesnt use any kind of 02 sensors either so im not sure what sensors they use for fuel control, i guess TP, IAT, MAP and coolant temp. I would be suprised if low fuel pressure caused dark smoke. If your fuel is that old you need to replace it with new fuel before proceeding. There are a lot of things that can cause black smoke. I have limited boat experience as I deal with Automotive as a profession. Just go over your engine with a fine tooth comb paying attention to your wiring and hoses and lines, look for loose vacume hoses, loose connectors and wiring chafes hopefully it will be fairly obvious like a loose connector or a loose vacume line. Sometimes you can find a fix a problem with a visual inspection of the engine. Hopefully this will be the case with you. When your boat does run fine does it still have the hissing sound? Hope this helps.

Knot 4 Me

+1. Get rid of the old fuel and see what you have.

Airpacker

The "hissing" sound is most likely the air moving through the idle air control valve. All MPI engines sound like that at idle.

Puking black smoke could be a ruptured fuel pressure regulater diaphram, a bad TPS or MAP sensor or a miriad of other issues BUT, two year old gas is NOT gas. Its garbage.

sassea

can it be an ignition modulator and coil????