2001 21V engine problem

[ploeffelman]

We have taken our boat out four times this year and after an hour of wakeboarding the boat sputters and loses power, for a little bit you can run at lower RPM until the boat eventually dies, you let it sit for a little while and it start back up and then when head back at low speed. When behind boat you smell gas and acts as if the boat is getting gas but not firing. We have replaced the water separator fuel filter, checked the fuel line for any restrictions, changed the distributor cap and ignition sensor but still does the same thing. Has anyone experienecd something like this? Mercruiser 315 hp engine

[Ryan Schilreff]

not sure if this is it, but below the fuel filter, look compltetly below, there are two wires, one red and black wire, make sure the black wire is connected as this goes to your low pressure fuel pump.

[R&T Babich]

What engine do you have and how many hours?
I'm guessing Mag MPI from the 315 hp, not a carb.
Does it do this each time you go out after about an hour?
Our 350 Mag MPI Ski does not have a low pressure fuel pump below the fuel filter.
Maybe the plug wires are shot.
There may be an engine fault code that would help.
Make sure you're getting around 23-25 psi of fuel pressure.
Make sure there is no water in the fuel/water separator by pouring it into a clear jar.
The symptoms sound like a time we had issues with water in the fuel from a marina pump.

[samw]

This may not help this problem but it will make it run better. If you don't know if the plugs, wires, rotor and cap will need replaced every couple years. I agree with R & T could be water or moisture in the take. Add some sea foam or stabli. I have the same year and motor. It's a strong motor. Try some of the above and check the fuel pressure.

[dogbert]

This may not help this problem but it will make it run better. If you don't know if the plugs, wires, rotor and cap will need replaced every couple years. I agree with R & T could be water or moisture in the take. Add some sea foam or stabli. I have the same year and motor. It's a strong motor. Try some of the above and check the fuel pressure.

I'd agree the cap may need replacing. You shouldn't have to replace the plugs more frequently than every 400 hrs.

How many hours are on the motor? Also, when was the last time the impeller was replaced?

[TeamAllen]

We have replaced the water separator fuel filter, checked the fuel line for any restrictions, changed the distributor cap and ignition sensor but still does the same thing. Has anyone experienecd something like this? Mercruiser 315 hp engine

He said he already changed out the distributor cap.

[samw]

He said he already changed out the distributor cap.

Team
Good catch

[ploeffelman]

No fault codes came up at the dealer
Impellar was changed in the spring
Put Stabil in it after the first time it shut down
Pulled water separator off and dumped into jar no water
motor has about 180 hrs.
do you think it has something to do with overheating? ( gauge reads 175 degrees when it shuts down)

I have not checked the fuel pressure yet

[dogbert]

175 is normal.

One thought I had was that maybe your fuel vent is clogged or pinched. What would happen is that it would create a vacuum in your fuel tank that would cause the engine to be starved for fuel (just like running out of gas). Once pressure in the tank equalized again, you'd be able to start it. Your boat burns about 5-6 gals per hour.

Your vent line should be in the observers compartment. Maybe there's something obstructing it in that storage area?

[R&T Babich]

175 is normal.

One thought I had was that maybe your fuel vent is clogged or pinched. What would happen is that it would create a vacuum in your fuel tank that would cause the engine to be starved for fuel (just like running out of gas). Once pressure in the tank equalized again, you'd be able to start it. ...

Our boat runs just under 175 deg, too.
That's a great thought about the vent line dogbert.
I had a car doing that once.
Our boats have a fuel/air separator (#1675) in the vent line which may be clogged: http://www.boatus.com/foundation/Fin...el.htm#summary
It could be bypassed for a test.
A fuel pressure test should tell something, too.
I added a small gauge that screws into a pipe fitting in the end of the fuel rail.
It's great for confirming there's good fuel pressure.
Does your boat do this each outing and after it sits a few hours runs good?

[Sharkbit]

Could it be vapor lock? These engines are notorious for that. If you are getting hot water draining back into the fuel cooler while the engine is shut off it could boil the fuel in the cooler causing it. I had some issues with that a few weeks ago. I think some people shoot cold water from the ice chest onto the fuel cooler and it fixes it. Could be a temp solution. I think mercruiser also offers a check valve that you add between the cooler and water neck on the engine to eliminate it. I would run the boat on a hose out of the water to ensure you are getting good flow through the engine. I had a brand new impeller go bad on me last week and it caused me fits.

Hope this helps.

[TeamAllen]

Can vapor lock occur while the engine is running?

[dogbert]

Can vapor lock occur while the engine is running?

Only if there is no vent to allow the pressure in the gas tank to equalize. It basically creates a vacuum.