SEDS (Sudden Engine Death Syndrome)

[FatBear]

I have a 1976 120 Mercruiser. It starts OK, runs rough while warming up but smooths out as the choke opens. Just when it starts to get warm it shudders and dies.

This started a few weeks ago. At that time I was able to run upstream to a fuel pump and it ran fine, but one the way home I tried to get on-plane and it just lost all power. The engine shuddered and sputtered the last mile and died as I pulled up to the dock upstream from my house. I thought it was water in the fuel, so I added a water separator. I got the engine warmed up and running nice and my wife got in with me and we made it about two or three hundred yards, not even out of the no-wake zone and it started sputtering so I headed home. It died just in time to glide into the slip. The next day I tried getting water out of all of the lines and dumping out the carburetor. It started fine, ran a bit rough until the choke opened, warmed up nicely, then died sitting right in the slip. It was getting progressively worse. So I took the carburetor apart to see if some sludge had somehow gotten inside of it, but it was pristine clean. Put it all back together again (yes, with a carb kit) and tried it again a few days later. Same thing only this time it dies just as it is getting warm to the touch.

So what could this be? There is a new fuel pump and rebuilt carb, new fuel, water separator, filters. I no longer think fuel is the issue.

So what happens as it warms up? The choke opens. But the choke on my current carb is electric and has been open for a while when this problem occurs.

Also, the thermostat opens as the engine warms up. So where does the water circulate before the thermostat opens and where does it circulate after the thermostat opens? Could water somehow be getting into the cylinders only when the thermostat is open?

A bit more background: a few years ago (right after I bought it) I had to have the exhaust elbow replaced as the water jacket had rotted through. Last year the water jacket on the head rotted through. Does this sound like the exhaust manifold could now be rotted through?

And if the exhaust manifold is rotted through does that mean the block is next?

Is there anything else that can be causing this particular problem? Hopefully something I can afford!

Thanks,

--FatBear

 

[Don S]

Re: SEDS (Sudden Engine Death Syndrome)

It could very well still be a fuel problem, something plugging up before the fuel pump.
Have a look at this thread for a way to test.

http://forums.iboats.com/showthread.php?t=283269

You could also hook up a remote fuel tank (outboard tank) directly to the fuel pump and see how it runs.

 

[reel clownz]

Re: SEDS (Sudden Engine Death Syndrome)

Well im gonna say im an expert but it sounds to me as if you have a bad head gasket. You replaced all filters, fuel, whatever. but as your engine gets hot, the thermostat opens and if you have a bad head gasket the water could be leaking into the cylinders choking out the engine. Like i said im no expert, but i would also check there. one way you might be able to tell is get the boat out of the water hook up the ears. Let it run get it hot. Once the thermostat opens if it stops flowing water out the exhaust it may be leaking into the cylinders. sometimes the head gaskets will go on the inside and you can never see or tell. Thats my guess. Good Luck!!

 

[FatBear]

Re: SEDS (Sudden Engine Death Syndrome)

Interesting idea. The head was replaced earlier this year and the problem has occurred since then. Perhaps the head just needs to be re-torqued?

Thanks,

--FatBear

 

[Silvertip]

Re: SEDS (Sudden Engine Death Syndrome)

One test you failed to do is when the engine dies and fails to restart, simply check for spark to rule out the ignition system. A coil getting hot can certainly cause the issue and since it gradually gets worse, the heat cool cycles get shorter and shutdown occurs more quickly. If this is a points style ignition, a condenser going bad can also cause the issue. A stuck (or sticky) anti-siphon valve can cause fuel starvation but that would be a rather long shot with the symptoms you describe. Anyway -- rule out spark before continuing to chase a fuel problem that may not exist. If there is indeed good spark then try this. When the engine dies, remove the flame arrester and look down the carb throat while you pump the throttle. If you see a good squirt stream from the accelerator pump nozzle you do not have a fuel delivery problem. You may still have a carb problem.

As for a bad head gasket, the leakage would need to be extremely bad to cause cooling water to be diverted from the cooling system. Besides, the water would still come out the exhaust but in the form of steam and water as it would have passed through the combustion chamber.

 

[6meter]

Re: SEDS (Sudden Engine Death Syndrome)

Right after it dies you need to check to see if there is voltage at the coil+ and/or fuel in the carb.

 

[fishrdan]

Re: SEDS (Sudden Engine Death Syndrome)

Put it all back together again (yes, with a carb kit) and tried it again a few days later. Same thing only this time it dies just as it is getting warm to the touch.

Did you adjust the idle speed and idle mixture screws after rebuilding the carb? Not just turning them X number of turns as the manual says, but adjusting them after the engine is warmed up, so the engine runs smooth.

- If the idle speed is too low the engine could die when the choke pulls off
- if the idle mixture is too lean or rich, the engine could die when the choke pulls off

(I hope this isn't obvious, some people don't have experience with carbs)

 

[GLENN M]

Re: SEDS (Sudden Engine Death Syndrome)

warms up? The choke opens. But the choke on my current carb is electric and has been open for a while when this problem occurs.

i dont think its head gasket, or water it would hydrolock if its leaking enough to kill motoryou need to follow checks and elimanate problems,as stated fuel spark and air,goodluck

 

[FatBear]

Re: SEDS (Sudden Engine Death Syndrome)

This problem was occurring before I rebuilt the carb and it was correctly adjusted (by the boat mechanics who everyone around here recommend, including other boat mechanics.) The problem is the same after rebuilding the carb, so I basically wasted my time doing that. (I thought it might be full of gunk, but it wasn't.) But since the engine dies just as it is getting warm it would be impossible to adjust the idle correctly. It started out way too rich and I leaned it out so that it ran smoothly at high idle. If I can ever get it to run warm, I will work on setting the idle mixture.

The problem is not occurring just as it comes off choke. The electric choke is fully "off" before the cast iron engine is ever really warm. The problem seems to be occurring a few minutes after the choke is fully open and the forward part of the exhaust manifold was just beginning reaching a temperature where I could touch it, but not hold it too long.

Unfortunately, we are leaving tomorrow and will be gone over a week, and my wife has banned anymore boat work today so I can pack. I have acquired a compression tester and will use that when I get back, check the spark, check the check valve at the fuel tank connection and anything else I can do. The boat is in a slip right now. If all else fails, I will wrestle the trolling motor onto the transom and drive it to the boat ramp (about two hours: can you say "pain in the back"?) and take it to the shop where the pros will fix it in a day.

Thanks, and if I do get it fixed I will post the solution.

--FatBear