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Mercruiser 3.0 stalls out after an hour

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mjricha

New member
Just purchased boat, runs fine, took to mechanic who said they couldn't replicate the problem.

All throttle positions work great, power is there, doesn't bog down or anything. Twice now, after running the boat for about an hour (not hard, mind you). When I slow down in a wake zone the engine just dies and will not restart. The battery isn't dead, cranks fine, you can see jets of fuel going into the carb when the throttle is pressed. But after an hour or so the boat will restart just fine like nothing ever happened. I have no idea why it's doing this, any help on where to start or what to check would be appreciated!
 
Have you checked for SPARK when the engine dies out?

You never said which version of 3.0 you have so specifics are hard to provide without those details.
 
makomark said:
Have you checked for SPARK when the engine dies out?

You never said which version of 3.0 you have so specifics are hard to provide without those details.
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I was on the water both times it happened so I couldn't then. Every time I try to replicate the problem in the driveway I can't.

It's a gen 1 alpha 1 120hp. The boat itself is a 1980 rinker trihauler
 
mjricha said:
I was on the water both times it happened so I couldn't then. Every time I try to replicate the problem in the driveway I can't.

It's a gen 1 alpha 1 120hp. The boat itself is a 1980 rinker trihauler
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Also....what would cause the spark to randomly stop after an hour or so of normal use?
 
mjricha said:
Also....what would cause the spark to randomly stop after an hour or so of normal use?
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A number of things - loosing 12 v supply to positive side of coil from bad key switch, loose or corroded wiring connections. Coil getting hot and eventually dying, points and or condenser.

Need to take a DVM with you and diagnose when it happens. Would also ohm the coil to see if it is still in spec. Get a spark gap tester so you can see if you have spark off coil, and at plugs, and strength of spark.

Are you sure it it not lack of fuel? if tank vent is plugged it is common to have fuel flow stop after 45 min or so
 
When was tbe last tune up, meaning points, rotor and condeser?

I also agree on possible fuel vent blockage
 
if it has the EST distributor, the pickup coil could be on the way out or so could the module...

DDIS is different beast altogether...
 
kghost said:
Original post shows 1980 boat...

If the engine is original, Its a point ignition
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As far as I'm aware the motor is original. When I bought it precious owner had recently replaced spark plugs and cables. I've spoken to him and he of course has no idea why it's doing this as it's never happened before.
 
Dieter said:
A number of things - loosing 12 v supply to positive side of coil from bad key switch, loose or corroded wiring connections. Coil getting hot and eventually dying, points and or condenser.

Need to take a DVM with you and diagnose when it happens. Would also ohm the coil to see if it is still in spec. Get a spark gap tester so you can see if you have spark off coil, and at plugs, and strength of spark.

Are you sure it it not lack of fuel? if tank vent is plugged it is common to have fuel flow stop after 45 min or so
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Would you happen to know the ohm values or where I can find them? I ordered a spark gap tester today

It is full, I filled it until excess gas came out the overflow on the side of the boat.

Also. I do not need the vent when I open the circular access hole between the front seats. Do you happen to know where the vent would be? Thank you
 
1. That is not an Overflow. Boats DONT have overflow ports for gasoline.

That is your gas tank VENT.

BAD THING TO DO!!! VERY DANGEROUS!
 
Dont need to ohm the coil.

Use a spark checker. If you have nice blue spark coil is good,
When the engine stops, recheck for spark.
If no spark then more troubleshotting needs to be done.
 
If you have been overfilling your gas tank and then run the boat and it dies,

Most likely its your falt.

If the gas tank cannot vent then the fuel pump CANNOT overcome the vacuum created.

Please clarify how much gas you have in tank when this issue ocurrs!!
 
kghost said:
If you have been overfilling your gas tank and then run the boat and it dies,

Most likely its your falt.

If the gas tank cannot vent then the fuel pump CANNOT overcome the vacuum created.

Please clarify how much gas you have in tank when this issue ocurrs!!
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Ok, the first time I filled the boat I realized that the tank gauge was broken. So I accidentally over filled. I didn't do it on purpose. Now the Guage is fixed and curently is between 3/4 and full. So i probably used an 1/8 of a tank both times before it happened. Before I go out next time I won't fill the tank. So since gas came out when I filled it the first time the vent must be clear then I'm assuming.
 
Yes you are correct, but if the vent line has a loop in it, and I have seen them this way, gas will act like a clog.
You can blow with your mouth from the vent port back to tank to see if it is clear.
I know it sounds weird but I have done so many times. Using pressurized air can blow out the screen at vent port on side of the boat
 
mjricha said:
Would you happen to know the ohm values or where I can find them? I ordered a spark gap tester today

It is full, I filled it until excess gas came out the overflow on the side of the boat.

Also. I do not need the vent when I open the circular access hole between the front seats. Do you happen to know where the vent would be? Thank you
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you can google this stuff as easily as I can... get a factory manual as all this is in there. OEM merc manuals are really, really good well worth the $.

Primary Resistance .60-.80 Ohms
Secondary Resistance 9,400-11,700 Ohms

As jack pointed out when it dies check for spark. You can check or not check the coil a head of time, if you have a weak spark - basically wont jump much of a gap and is orange vs white or blue... It rarely is the coil but good to rule out.

Basically you need to determine when it dies is it missing spark or fuel and go from there. When it dies use the gap tester off the coil and at the plugs to determine if you are loosing spark. No spark - chase that down. If you have spark dribble some gas down carb if it fires chase the lack of fuel route from carb back to the tank. Make sure your vent is open, crack the fuel tank when it dies if it sucks in due to vacuum that is one common sign of clogged vent.
 
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