Mercruiser 5.0 L Engine Failure

[Frederick R. Dent III]

I have a Mercruiser 5.0 L alpha one I/O V-8. SN OF280196.
The engine starts fine. After about 40 minutes of cruising at 1000-1200 rpm, the engine momentarily runs rough and then stops. Repeated cranking of the starter on both batteries has no effect. The engine does not even try to start. DEAD!. When I wait several hours and the engine cools down, the engine starts on the first crank and runs great. The next time out, the scene repeats itself. Engine failure occurs after 40 min of low rpm. I'm getting tired of being towed to shore. My wife says SELL.
Within the past year, I have changed out plugs, rotor, and cap. (Not the coil). Four weeks ago, I replaced the shift cable. Is there any connection there? Is heat somehow causing a short in the coil? The wife with great ears heard a clicking sound before engine failure. Would appreciate some ideas.

Frederick R. Dent III

 

[Uraijit]

Re: Mercruiser 5.0 L Engine Failure

You need to find out WHY the engine is dying, rather than just throwing parts at it.

When it dies, are you getting spark to the coil?

 

[lkbum]

Re: Mercruiser 5.0 L Engine Failure

Sounds like vapor lock to me. When cruising at low speeds, your engine compartment is getting less ventialtion and may be getting fairly warm. Depending on how your gas line is routed, the gas line may be getting pretty warm. Enough to "boil" the gas in the line, turning it to vapor and the engine dies because it needs liquid gas, not gas vapors. If this occurs while running, it will first run rough, then die. After it cools down, it will start up and run fine. Try running with the hatch open and see if this makes a difference. Also look where your gas lines are routed. Any chnace they are getting too much heat from the engine (this has been a common problems of 5.0 and 5.7l mercs.

 

[John_S]

Re: Mercruiser 5.0 L Engine Failure

OK, seperate thread now, thanks!

As Uraijit re-enforced, you still need to isolate fuel from electrical, and why I asked:

"It sounds like you are chasing electrical. Did you varify there was no spark? or that the carb still had gas? ie you pushed the throttle a couple of times and got good streams from the accel pump nozzles?"

Can you recreate the problem at the mooring dock, or if a trailered boat, on muffs?

The shift interupt switch will ground out the ignition, but that is usually a position adjustment error, streached cable, consistant problem vs heat/time related. Start back at the fuel/electical decission point first.

 

[chiefalen]

Re: Mercruiser 5.0 L Engine Failure

I'm going to take a shot in the dark.

Check the vent it clear, sounds to me a vacuum condition. Check the fuel pickup screen in the tank. It clogged, all other filters clean, the one in the fitting bye the carb, fuel water separator.

No over heating?