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Author Topic: Mercruiser 5.0 stalling at idle when hot  (Read 262 times)

Offline CaNINE

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Mercruiser 5.0 stalling at idle when hot
« on: September 04, 2017, 06:58:05 AM »
We have a 2009 24' SeaRay Sundancer with a 5.0 Merc SeaCore and Bravo3 drive. It's been a great running boat for us until this summer. On three different occasions now the engine has stalled at idle and won't restart until it cools down. 

On a cold start everything is fine, boat runs smooth, runs great with no issues. We cruise around for a while and come off of plane into a no wake zone, putts at idle speed and after 10 - 15 minutes of running at idle speed it stalls out in gear.

Fortunately this has always happened where I'm able to flag down another boater to tow me in or I drop anchor and call towboatUS for a recovery. Thankfully I have the unlimited towing membership.

My first thought was a bad IAC valve. I took it to a very reputable marine service in Tacoma. They came to the same conclusion and said the IAC was sticking when hot. We replaced IAC.

First time in the water yesterday since the repair. Same problem. Ran for about an hour at 3400 rpm at cruise, came off plane and idle'd around in gig harbor for 20 minutes then the engine quits.

My next thought goes to something in the ignition system getting hot like the coil or maybe the oil pressure switch is malfunctioning and sending a kill to the engine.

Any bright ideas?

Needless to say it is a very unnerving feeling to have no power and be adrift in the puget sound. 

Offline BDildine

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Re: Mercruiser 5.0 stalling at idle when hot
« Reply #1 on: September 04, 2017, 07:13:27 PM »
ign modules can do the same thing when they get hot. get an inline spark checker and see if you can replicate the problem somewhere safe to test (lake or such), and if no spark, check to see if you have power supplied to module/coil, that should help narrow it down
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Offline CaNINE

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Re: Mercruiser 5.0 stalling at idle when hot
« Reply #2 on: September 07, 2017, 09:22:36 AM »
ign modules can do the same thing when they get hot. get an inline spark checker and see if you can replicate the problem somewhere safe to test (lake or such), and if no spark, check to see if you have power supplied to module/coil, that should help narrow it down

Thanks. Going to run some in the water tests and try to recreate the failure, check for spark and fuel pressure issues.

Offline CaNINE

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Re: Mercruiser 5.0 stalling at idle when hot
« Reply #3 on: September 12, 2017, 07:24:36 AM »
Well we found the problem. The Cool Fuel Module had internal corrosion and was restricting flow to the high pressure fuel pumps. Once the engine reached temp it the pump would get hot and shot down. 

New fuel module on order. Unfortunately it's a gold plated part.

But I should be back in the water for the weekend.

 

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