2002 Mercruiser 496 stalling feels like fuel issue

[gil442]

So I bought this boat last week. 1987 Skipjack Fisherman 25 repowered with a 496 Mag and Bravo outdrive and 32 pitch prop with through hull exhaust. The guy I bought it from is disabled and older was the original owner. My first sea trial the boat was at 1500 rpm till out the no wake zone then I give it gas to where it stumbled and sputtered till I backed the throttle off and it recovers at idle. I took him the boat back and he said "shoot I just spent 6 grand 2 years ago fixing that" He had the fuel pump replaced all the injectors the manifolds and the plugs and impellar done. He used the boat once in 2 years and supposedly it ran fine. He took the boat back from me filled up the tank added some fuel treatment to the tank (full) and replaced the fuel water separator (never been replaced) and I took delivery and paid a lot of money for the boat cash. Next trip out I make it about 15 miles to the Golden Gate bridge and it starts stalling again like it did originally. It feels as if it runs out of fuel. It will runs at idle or low rpm all day without a hiccup and sometimes you Goose the trittle and it picks up and starts to move out and it will stay or it conks out right away and you have to bring it back down to idle and start again. The engine never dies it just cannot maintain a load (most of the time) We both figure there is water in the fuel and pull the water separator again and dump out its contents re install it and start going for it to just fail again very shortly. The local marine shop I talked to thinks maybe cracked pick up in the tank and said to use an aftermarket electric pump and pull fuel with a clear hose and watch for bubbles to see if the tube is cracked and no go it flows fuel just fine. Today I just got done draining 80 gallons of nasty gold **** fuel from the boat and boat a new inline filter and another fuel water separator filter and plan on driving to the water again and giving it another shot but after reading a bunch of threads on here and other places about fuel pump problems associated with this engine I wanted to post up on here and see if anyone could offer some help!!! I just bought this boat and paid full price and it wont run properly please help!!!!

 

[Fun Times]

Hi there, welcome to iboats!

Since you found bad fuel inside the fuel tank then there's still a good chance that there's still a problem with the boats fuel system whether it be the fuel tank anti siphon valve which is the hose barb fitting the fuel hose connects to at the tank, still a cracked fuel tank pickup tube like suggested, the screen at the end of the pickup tube is/getting clogged at certain times of boat movement/fuel demand or the internals of fuel hose is blistering causing a flow disturbance.

You'll need to buy yourself a fuel pressure test gauge and connect it to the engines fuel rail shredder valve on top of the engine and see what your fuel pressure is before and during the event. (should be around 43ish psi) Also before you head out, make up a small 3 - 5 gallon external fuel tank with a new fuel hose and be ready to install it out on the water to see if the problem repairs itself while watching the fuel psi gauge. Also it would be a good idea to connect a temporary clear hose between the tank and engine fuel filter assembly.

The local marine shop I talked to thinks maybe cracked pick up in the tank and said to use an aftermarket electric pump and pull fuel with a clear hose and watch for bubbles to see if the tube is cracked and no go it flows fuel just fine.

Keep in mind that it seemed to run good when you completely filled up the tank but after using some fuel, the engine ran bad again. If the fuel level at the time of your clear hose testing was covering any possible cracks while sitting still (say on the trailer) then you may not notice it right away. This test is sometimes better done while under way. But since you found bad fuel in side the tank, continue to resolve that issues until you believe it's not the problem any longer.

You need to know if it will run 100% while on an external fuel tank that way you know if you need to work on the boat side or the engine side....Or both.

Let us know, good luck.

 

[wahlejim]

How full was the tank when you bought it? How fresh was the fuel? Was it all changed out? If he only ran it once in 2 years, and the fuel is that old, you may have started with bad fuel. Topping off with good fuel and treatment isn't enough after the fuel has already gone bad.

Isolate the problem. Run off of an external fuel tank as Fun Times suggested and rule out engine problems as well.

 

[alldodge]

Howdy

Your engine has two fuel pumps, one of which is a boost pump below the fuel filter and feeds the high pressure pump in the cool fuel module on the port side. The boost pump should read 6 PSI with engine running. The boost pump is a low pressure pump and most spec out as anything between 4-6 PSI but manual indicates only 6 PSI.

There is a vacuum line going down to the high pressure regulator on the port side, if you place a Tee fitting in line you should read between 15 to 21 in Hg.

With all the crud you found in the fuel tank it could have clogged up some stuff as Fun Times mentioned including the regulator