Ideas on what would cause boat to die?

[timmyjane]

99 4.3 dies after running a while. Boat will run fine for about 30 or 45 mins and then will begin shutting down. Once the boat shuts down it will start right back up but then will die again in 15 seconds to 2 mins. No warning alarms.

The alarm does work because it went off when the gear oil was low. However I am not sure if the oil pressure side of the alarm works. When the key is turned on there is an audible beep but it does not have a long drawn out beep like my last boat did. Per Mercury CS this is ok and it is working like its supposed to.

Where should I start looking on this? Im wondering if its not one of the sensors shutting the fuel pump down.

 

[Leardriver]

A plugged fuel tank vent?

 

[timmyjane]

What's the best way to check that?

 

[alldodge]

What's the best way to check that?

When it dies, open the gas tank fill cap, and IF you hear air rush in, or it starts and runs without issue, that's the issue

 

[timmyjane]

Ok. Thanks. Any other ideas?

 

[Scott06]

As above and when it does die check fior spark with a spark gap tester to see if coil is getting hot and croaking.

 

[alldodge]

Ok. Thanks. Any other ideas?

From what your telling us so far, a clogged vent would be the most probable cause. If you have more info of what is happening it could help in determining other possibilities

 

[timmyjane]

Not the gas vent. Boat gave lots of trouble this weekend. Same symptoms as always. Boat will run good for a while then begin dying. It will fire back up and run for generally not more than 15 seconds before it cuts off again. However, there may be a time or two thrown in while limping back to the dock that itll run for a minute or more.
Opened the gas cap and there was no hiss and it still followed the same pattern when trying to run with the gas cap loose. Going to go ahead and order a coil and I guess well see what happens then.

 

[alldodge]

What is your engine serial number?

Being a 99 I'm guessing it has a carb and electric fuel pump. An issue is we don't know if you have a TKS, Merc, 2 or 4 barrel carb.
I would like to start with the basics and try and figure out is it spark or fuel your not getting. Getting a coil may fix but there has been many thousands of them replaced with no help.

Pull the fuel filter and see if it is full, then dump the contents into a baggie or something clear so you can see if there is anything other then clean gas. Suggest putting a voltmeter on the positive terminal of the coil and when it dies see if the power is going away.

When you go to restart the motor do you have to crank for a bit before it fires?
When the motor is running do you hear the fuel pump running? On put your hand on it and can you feel it running?

 

[timmyjane]

The engine serial is 0L329521. I was thinking that the carb is a Merc 2BBL.
The motor seems to pretty much start right up after it dies. I haven't checked the fuel pump because I didn't think that would be the problem. I assume that it works because the motor will run for a while before it dies and then will fire back up.
It seems that either something critical for running gets warm and then quits working for something else gets warmed up and then shuts off either the ignition or fuel. I was originally thinking it was something similar to the oil pressure cut off killing the fuel pump. But we don't get a warning alarm so it is confusing.

 

[alldodge]

Thanks for the S/N it helps with how the motor was built, and its a 1998 model
http://www.mercruiserparts.com/4-3l-gen--2-bbl-gm-262-v-6-1998-1

If it was running out of fuel it would spit, sputter and then die. Turning the key it would not fire back up quickly. If it was fuel the key would crank the motor a few seconds so the fuel pump would fill the carb and it would run again for a short time.

So if its dying quick, then its electrical

 

[timmyjane]

That makes sense. It'd have to say electrical then. It probably doesn't have anything to do with the problem but at times the starter can be very slow to start. Like how it would sound when the battery is almost dead. Most of the time it hits quick and hard but occasionally, especially when cold, it drags.

 

[alldodge]

With the starter dragging, I would suggest looking at the ground connections. Start at the battery and inspect the cables, bend them around and look under the insulation if you can. Look closely at the negative cable the connection to the block. Then look at the 10 pin engine harness connector. Remove it and check the pins. Then work your way up to the key switch and its contacts

 

[timmyjane]

Not ignition coil. Installed new coil and no change. What ever it is seems to have gotten worse. The time it takes to get to the point of cutting off has gotten shorter and once it reaches the point of cutting off, about 15mins now, the boat will run for 12 seconds and die.

 

[alldodge]

Put a voltmeter on the + terminal of the coil and wait for the motor to die while watching the meter.

Also would like to know if the fuel pump is running. Would also like to know what kind of pressure you have at the carb