Random Dying, HELP!!

This happened the weekend before last:

Little background. 96 Malibu Sunsetter, 350 Mag Mercruiser EFI with 345 hours. This season I've taken her out 3 times. ( I was gone for almost 4 months) In March, before the 3 runs, I had a complete tune up/service/detail done by a local, well known dealership that is in good standing. Tune up included spark plugs, spark plug wires, distributor cap, rotors, fuel filter, impellar, thermostat/temp regulator etc.

This last time we were out, we were wakesufing for about 30 min to an hour. Killed the engine to move ballast around and when I started her back up, she fired up for a sec and died. Tried starting her again and she just cranked over and over like it was out of gas. Would start then die, start then die. So I pulled the neutral switch, pinned the throttle and started cranking her again. After close to 1 min of off and on cranking it finally started. So we throw in the boarder and get on with some fun. After another 15-30 min we stop to move ballast, I kill the engine and it does the same thing.

So after drifting oh so close to a stump graveyard she finally starts again. This time I'm heading back to the dock for fear of being stranded in huge stump minefield. I pin it to about 4400 RPM, thinking I can run whatever is wrong out of it and she dies.

After floating around for another 30 min or so (and throwing ancor so not to float back to the stumps) I finally get her started. I pin it wide open, and make it back to the ramp. Funny thing is I turned her off to get the truck and get the trailer in the water, thinking she would not re-fire. I get back in and she fires right up like nothing was wrong. I try it multiple times and she fires up like she was brand new. What the hell is wrong?

This happened yesterday:

This time I didn't shut off the engine for close to 4 hours before I decided to give it a break. Afterwards it ran fine for about 15 min then started acting up again. After about 20 min of problems, it started up and didn't have another problem for the rest of the day... Someone mentioned that because of the humidity in Houston, and the fact that I have had the boat in storage for 4 months w/o running, that I probably have water in the line... Any ideas?

I had this happen a couple of years ago- it turned out to be an ignition relay. Also make sure your groung to the alternator is tight- if for some reason it came loose, the electronic ignition will not let the boat start- I'd tighten that first, then try the relay- it costs about 15 bucks and you can easily replace it yourself. good luck- I hate problems like that!

Is the motor TBI?

If so it's almost certainly the VST Tank/Pump.

If it's the tank, you have to take it apart, clean it out thoroughly, buy a $75 o-ring, put it back together. and see if it happens again, if it does the VST Pump might be bad and be ready to shell out up to $1400.

Also, has this been happening on particularly hot days? These motors do not have a Fuel Return, unburned fuel just hangs out waiting to be vaporized and cause vapor lock like a mother

Not sure what the TBI is. It is the 290hp 350 Magnum Mercruiser EFI Mulit-port injection.

Will, where is the Ignition relay? Is it in near the fuse panel? I'm not to mechanically inclined when it comes to boat motors, now if it was a 2 stroke engine I'd be in luck!

I had a similar problem and if you search vapor lock you should find similar experiences to yours.

My cure has been running the blower when I shut down. Others have insulated the fuel system.

Brandon the rela is on the top of the block next to the air filter. I have the same engine. Check your manual for which module is the ignition relay. Also- try pulling a plug and seeing if you're getting a spark- touch the plug to the block when you're turning it over and if you're getting a spark- it's probably a fuel issue. If you're 100% certain the dealer changed the fuel filter, then i'd check the ground on the alternator and change the relay- it could be an intermitten problem. Good luck.

I also had this issue at the beginning of the year. Loose ground wire on the fuel pump.