3L Mercruiser stalls out when cruising

[Zepher]

I have a 1989 mercruiser 3l I/O which idles fine , but starts to flutter and stalls after it has been run under load for 20 minutes or so. It won?t restart untill I wait for 30 minutes or so, and then dies again after a few minutes. The engine temp is fine, I have changed the fuel filters, coil, wiring harness, plugs, overhauled the carb. I have noticed that there is a fair bit of blowby gas from the valve cover that is sent to the carb air breather. Could this be a problem? I would appreciate any help. Thanks, Zepher

 

[jerryjerry05]

Re: 3L Mercruiser stalls out when cruising

If you replaced the coil did you replace with a resistor coil?If you have blow-by then you need to do a compression test.Post the results.
While your testingnce the motor runs for a bit feel the coil to see how hot it is.If it is so hot it burns then it's possibly bad.It should be hot but not too hot to burn.Volt meter at the positive side of the coil then neg side.What is the voltage? Post the results.Jerry

 

[Zepher]

Re: 3L Mercruiser stalls out when cruising

Thanks for the reply...It will take a few days to check this out, due to the weather. I will post results. Zepher

 

[chiefalen]

Re: 3L Mercruiser stalls out when cruising

Did you bye chance check the tank vent to see you don't have a vacuum condition.

When it cut off the motor take off the fill cap and see if you hear a whoosh of air.

The fuel pickup tube you know theres a filter there.

And the anti-siphon valve you checked that also?

Fuel pump giving you 4-6 psi?

The oil ok?

 

[Zepher]

Re: 3L Mercruiser stalls out when cruising

Thanks for the info. I won't get out in the boat for a few days, but I did have a look at the gas tank vent, and the screens are clear, so I tried to blow air down the vent tube and it seems plugged. It pressured up and exhausted back out the vent, when the air was removed. Should it not just go into the top of the tank? Thanks...Zepher

 

[chiefalen]

Re: 3L Mercruiser stalls out when cruising

No, you should have blown it out the other way from the tank to the transom.

But we know it ain't that, now.

You check all the filters yet?

After you confirm the filters are clean, beg borrow, steal a external tank and run it with clean gas, and if the problem is still there post here.

How does the engine oil look?

And the compression?

 

[Zepher]

Re: 3L Mercruiser stalls out when cruising

I will be taking the boat out Sat and will do a compression test cold and warm. I will also tube it into a spare jerry can. Oil looks good, no signs of water. I disconnected fill hose from the gas tank and siphoned from the bottom, and no signs of water. I confirmed the vent line is clear. I checked the coil and it is an external resistor type. I ran the boat in the driveway with earmuffs on it for 45 min and it purred like a kitten???The coil was only warm to touch, and the voltage was 9.7 on the pos and 5.6 on the negative.

 

[gdombroski]

Re: 3L Mercruiser stalls out when cruising

And the anti-siphon valve you checked that also?

A sticking valve will cause similar problems. Replace for about $15.

 

[chiefalen]

Re: 3L Mercruiser stalls out when cruising

Compression check will tell the story with that.

Or a vacuum check.

Tell you what vacuum is better.

Heres the link.

http://www.secondchancegarage.com/public/186.cfm

 

[Zepher]

Re: 3L Mercruiser stalls out when cruising

I just removed the anti syphon valve, and found a piece of plastic holding the ball slightly open. I hope this is the problem, I removed the debris and the ball now appears to work properly. I can see how this could cause it to be starved for gas when crusing if the ball was stuck, hense restricting the gas flow, but am not sure why it would not restart until I let it sit for 30 minutes or so. I will take the boat out Saturday.

 

[chiefalen]

Re: 3L Mercruiser stalls out when cruising

The fuel pickup tube you check that, should be a screen on that.

Your running along and garbage gets on the screen and shuts down the motor, you wait and the garbage floats off.

You start the motor it's happens again and again,

And the other filters, the one in the carb fitting?

Fuel pump?

 

[Zepher]

Re: 3L Mercruiser stalls out when cruising

Looks like the anti-siphon valve did the fixed the problem...It is snowing here now, so i guess I had better winterize it....Thanks for the great advice form everyone...Zepher.....