Bizarre engine behavior. Help needed!!

[Tdady]

So here's the situation.. I have a 2004 380 Sun Dancer with twin 8.1ls. The boat just turned 500 hours and has been meticulously maintained. Over the past couple of outings, after running at speed (~25 MPH @ 3250 rpms), when I come down off of plane and the engines are at idle, 750rpms, the port engine will randomly just drop out. By this I mean it will act as though the key has been turned off then right back on. When this happens it is accompanied by an alarm. On two occasions the engine has actually shut off. Last week I changed the idle air control valve and the map sensor. This week the problem is actually worse. Obviously I'm missing something.:smt100

 

[480ces]

When was the last time spark plugs were done?

8.1s are sensitive, I've seen plugs that looked just fine but new ones cured similar stall issues. How does the boat run at WOT?

 

[GreatEscape]

Sounds like the main battery supply is dropping off. Try wires to main engine breaker or cable feeding engine.


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[Last Dollar]

Isn't there a fuel pressure sensor on these engines? If you are getting an alarm then it must be logging a code and can be read by a scanner. I'm no expert but somehow plugs and battery connections don't seem to be problems that would trigger an alarm.

 

[480ces]

I'd guess he's getting a raw water pressure alarm due to the engine nearly stalling.

If the plugs havn't been done they are due anyways at 500 hours...How is higher RPM running?

It's possible you got a bad IAC, I've heard of that before.

 

[Tdady]

I was thinking about a fuel pressure regulator as well but don't know where to find it yet. I was also thinking maybe the "brain". I plan on having it scanned this week. We'll see what that comes up with.

When was the last time spark plugs were done? Plugs and wires were done less than 20 hours ago.

8.1s are sensitive, I've seen plugs that looked just fine but new ones cured similar stall issues. How does the boat run at WOT?

Boat runs great at WOT.

Sounds like the main battery supply is dropping off. Try wires to main engine breaker or cable feeding engine. All the connections to the engines have been gone over and are good.


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Isn't there a fuel pressure sensor on these engines? If you are getting an alarm then it must be logging a code and can be read by a scanner. I'm no expert but somehow plugs and battery connections don't seem to be problems that would trigger an alarm.

 

[ziekman@cox.net]

Your fuel pressure regulator sits in the top of the cool fuel module cap. Have you checked the modules for the paint flaking issue (well known and documented)? If not, you are going to want to pull the regulators and caps to take a peek - they may be clogged with paint flakes.

 

[GottaLuvit]

I had a similar issue on 1997 7.4's. It was the electronic module in the distributor failing.

 

[Tdady]

Your fuel pressure regulator sits in the top of the cool fuel module cap. Have you checked the modules for the paint flaking issue (well known and documented)? If not, you are going to want to pull the regulators and caps to take a peek - they may be clogged with paint flakes.

Thanks Art, after reading all I can find about this issue Im scared to think what I might find when I open up the module. The last post I found on the subject was from earlier this year. Has anyone been successful in getting Merc to help pay for their piss poor engineering??

 

[rondds]

Required reading for 8.1 guys...

http://clubsearay.com/showthread.php/66600-Replacing-Cool-Fuel-III?highlight=

 

[480ces]

His boat is an 04 though so it could very well be CF2. Do you have a spin on water sep/fuel filter or the cartridge style?

 

[Tdady]

I have a spin on filter as well as an in line filter. Im thinking I have the CF2???

 

[480ces]

Yeah, that would be CF2. I honestly haven't heard of issues with the older ones and never had any myself when I had 8.1s.

If you're making WOT I'd be surprised if it was a fuel delivery issue. I'm still leaning towards you possibly having installed a bad IAC. You said your stall/stumble happened around 750rpm...can anyone chime in with what RPM the IAC is in play up to since 750 isn't idle.

 

[Pair-A-Dice]

I have the same issue on my Starboard 8.1L Horizon. Here are some parts have I replaced that did not solve the issue. Hopefully this can save you some money on parts.
Both high and low pressure fuel pumps and fuel cooler. Also changed both in-line fuel water separators, and swapped out relay switches on top of engine. Checked battery, connections, engine grounds, idle air control valve, and map sensor. Best of luck on your situation! If/when you find the cause please update the thread.

 

[Tdady]

I have the same issue on my Starboard 8.1L Horizon. Here are some parts have I replaced that did not solve the issue. Hopefully this can save you some money on parts.
Both high and low pressure fuel pumps and fuel cooler. Also changed both in-line fuel water separators, and swapped out relay switches on top of engine. Checked battery, connections, engine grounds, idle air control valve, and map sensor. Best of luck on your situation! If/when you find the cause please update the thread.

Thanks Pair-A-Dice I'll try and keep this going until I have it resolved and will post the results once I figure it out.