Strange engine issue???

[Dents]

Last weekend I experienced a strange issue.... we had pulled away from the dock and were waiting for our friends to load up their boat and pull out as well. We were sitting at idle for maybe 5 minutes when all of a sudden it sounded like the engine was sucking wind. I put it in gear and there was no power. I engaged fast idle and no power. Finally it just died and would not start. It would crank, fire, then die. After a few minutes of this we had our friends pull us back to the dock where we tied up and jumped in their boat for the rest of the afternoon. When we got back to the dock we began to diagnose the issue and found nothing wrong. We had fuel pressure, spark, air and vacuum but still would not start. Finally after about 15 minutes of thinking and random attempts of cranking it started. Ran fine and has ever since!!! It is a Merc 350 MPI so no carb issue. My 2 thoughts... When we were sitting at idle everyone was sitting in the front sections of the old style 21i so nose was waaaaay down and back was up. I dont see how that could do ANYTHING???? Just seems too coincidental. Thoughts?? My other thought is bad gas somehow. We filled up that morning and might have filled with non 100% gas(alcohol/eth)????? Maybe just a freak deal. Any thoughts?

[Jason B]

Was the engine getting enough air?

[Dents]

when we were trying to diagnose we pulled the cover and spark arrestor off. everything looked fine and still wouldnt start for a while. I did clean the spark arrestor screen before reinstalling. It had very slight carbon build up but not enuff to restrict air flow i would say.

[lightning59]

Fuel/Water separater maybe? How long since last change?

[jwanck11]

How long has the engine been running well since?

[Dents]

I change the fuel filter every year.... I have run the boat about 20 minutes since at high speed and idle for a bit as well. Runs perfect.

[H20SKIER14]

I would have said vapor lock because that's the same thing my 21i with a merc does every once in awhile but usually if I let it sit for a few hours it will start right back up and be fine. Another thing I have done is pull the fuel filter and it is usually half full when it does it so I put a little gas in it and it runs fine. Also when it does it you can let all the air out of the fuel system with the valve at the front of the fuel rail I know this isn't the safest thing though. Hope this helps!! Here is a link to another discussion on it http://www.tigeowners.com/forum/showthread.php?t=7499

[philwsailz]

Check your Idle Air Control sensor and make sure it is firmly attached to your throttle body.
If it is loose it will make the air sucking sound you describe.

If loose or intermittent, it can also prevent the motor from running well...

[dogbert]

I would have said vapor lock because that's the same thing my 21i with a merc does every once in awhile but usually if I let it sit for a few hours it will start right back up and be fine. Another thing I have done is pull the fuel filter and it is usually half full when it does it so I put a little gas in it and it runs fine. Also when it does it you can let all the air out of the fuel system with the valve at the front of the fuel rail I know this isn't the safest thing though. Hope this helps!! Here is a link to another discussion on it http://www.tigeowners.com/forum/showthread.php?t=7499

That doesn't sound like his issue. If I had to guess is, it would be bad gas. I'd also check your distributor cap for carbon build up. If there is some, it may be time for a cap/rotor change. Mercruiser's Tournament Ski Mag engines are notorious for going through distributor caps. It still sounds like bad gas.

[Dents]

maybe a combo of bad gas contributing to the vapor lock? I am trying to learn more about vapor lock on other threads and sounds like the 350 Merc has issues with this? Can we rule out that all the weight in the front of the boat had anything to do with this??? That has really been bothering me cuz I dont see how there is any possible way withthe nose down and the stern up could effect anything???????? BUT I have never had the weight in the boat like that and never had ANY engine issues. Maybe just a coinsidence?????

[noworries]

Can we rule out that all the weight in the front of the boat had anything to do with this??? That has really been bothering me cuz I dont see how there is any possible way withthe nose down and the stern up could effect anything???????? BUT I have never had the weight in the boat like that and never had ANY engine issues. Maybe just a coinsidence?????

Nose down will have nothing to do with it unless you were way low on fuel and you were sucking some air along with fuel as the boat bobbed around. Fuel is drawn from the rear of the tank. If you DID suck some air into the fuel system, it could have taken a while and fits and starts to get it worked through the lines and injectors.

[Dents]

Tank was full so no air should have been sucked in that way.

[formandfunction]

The air sucking sound is the idle air bypass valve trying to compensate.If something goes wrong and the engine starts to die the computers programmed to idle up where it should be.With a metal screen for a aircleaner you can hear it pretty well.That would tell me the computer is not the problem which leaves fuel and spark.
Spark plugs,wires,cap would be a more consistent problem not having many variables to change the problem so you could rule that out.The coil might be bad but would be sensitive to heat expanding and grounding out.
I would say fuel is the culpret either pump,water in the line,something getting stuck in the return diaphram or vapor lock.
I would start by eleminating any chance of bad gas or water in the gas with some kind of treatment,new filter and some good high octane gas.If that don't work buy a gauge with the fitting that screws on the bleeder in the fuel rail.$25.Without the boat doing it again your pretty well stuck but if it does you should be ready to figure out why.Gauge will tell you pump,air in the line would tell you vapor lock.

[dogbert]

Usually, vapor lock prevents you from starting. I've never had the issue where it kills your boat while idling because the fuel should be cooled. If you're having overheating problems, then maybe, but that didn't sound like it was the case.

One way to tell for sure is to leave the blower running next time and see if it does it again.

[murphini]

This may be off topic--but check the ground wire from the battery (switch) to where it is attached to the engine. If loose/flaky, the ecm may not be getting signals, which may cause your problems of bad idling, not starting...etc. Ours came off, boat died becase ECM received NO signals. Was a very easy fix. I saw a post from last year about a loose ground wire.

Wouldn't hurt checking.