intermittened loss of RPM 340DA

M

mares1

Member
Apr 3, 2007
44
Sea Bright
Boat Info
340 Sundancer 2002
Engines
6.2 merc
2002 340DA 6.2 merc.

The engines worked fine until I went above 3800rpms ti get on plain. The port engine's rpms fluctuated at the top end. After a few minutes it seemed to clear up. Then after we achored for a few hours the problem reappered on the trip home. A friend suggested the fuel pump which is an expensive fix.

Are there any other thoughts.

Thanks
 
It does sound like a fuel flow problem. How about the fuel filters? Have you replaced them in the past year? If not, consider doing that first. What about the fuel itself? Any possiblity of bad fuel? I know you said it's only on one side, but due to genset... I've been known to add gas to only one side at a time.

Since you didn't mention it, I assume that you're not getting an error message/warning of any kind. This could also be an electrical issue. I've read of other guy's spark plug wires coming loose/off. Any smell of gas when this is happening?
 
Thanks for the reply, gas is the same in both tanks, fuel filter was installed in the spring and there are no wires missing or gas smell in the boat.

Any thoughts into junk floating by at the dock got caught on the prop. But the would be a constant issue.

Thanks again
 
mares1 said:
Thanks for the reply, gas is the same in both tanks, fuel filter was installed in the spring and there are no wires missing or gas smell in the boat.

Any thoughts into junk floating by at the dock got caught on the prop. But the would be a constant issue.

Thanks again
Click to expand...

Definately dive the boat (snorkle/mask). You never know what you'll find!
 
Alex D is having the same issue plus generator issues. http://www.clubsearay.com/forum/showthread.php?t=13173

I had the issue with mine also but mine is an 8.1. My dealer looked at it and came up with nothing. I ended up pulling the engine wiring harness plug apart at the top of the engine, cleaning the contacts and checking the pins to be sure they are tight. With the same fuel in the tanks, the issue dissapeared and has not returned for roughly 20hrs of runtime. HTH SB
 
Newbie and I have been exchanging thoughts and ideas in the thread he linked to. I think my genny issue is unrelated and either bad plugs or a leaky gasdenser.

I now this fluctuating issue just appear during the past month. Never ever had any engine power issues since I owned the boat. I had all the fuel filters changed last week (2 per engine, two cheap water separator filters for 9.50 each and the expensive inline FI filters for $50 each) and went out to check yesterday, but the fluctuation issue is still there. Mine is on the starboard engine just like Newbie's was. I plan to do Newbie's main harness plug check and maintenance that he explaines in my thread he linked to. read also fwebsters post!! Very insightful!!

I think between the three of us we should discuss what we find out and help each other out.

BTW I'll buy Newbie a beer or two from here if his main harness plug repair fixes the issue. If it is the cause no dealer would ever find it. It is one of those lucky strokes finding these issues sometimes.
 
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Wow, I have had this problem for months. I have a 2002 340 w/ 6.2 (320's). I get a drop and subsequent increase of RPM's after the engines have run for awhile. If I'm crusing at 3800 RPM's I will get a drop to around 3500 or 3600 ON BOTH ENGINES and then it goes back to 3800 and will sometimes climb to 4000 or so and then level out. My Sea Ray dealer hasn't a clue. Did you get through this? Was it a gas issue???

enablers2
 
sfergson727 said:
Does your local fuel use ethanol? If so, you can expect the other engine to be acting up very shortly. We spent ALL summer tracking down the same issue in my friend's 340. After changing multiple fuel filters, swapping ECM's and having a tech go with us on the lake with a fuel pressure sensor hooked up, we finally came to the conclusion that the ethanol was either breaking down, or attaching itself to moisture in the fuel, or both. You could see the inconsistancy in the fuel when you looked at it (after draining from the filter).

His symthoms were this: When at cruise power (3300-3700 RPM) his engine would lose 150-200 RPM for varying amounts of time, usually 30 to 60 seconds and then recover. You could hear the RPM loss as well as seeing the indications on the instruments. There was a slight roughness in the engine when it dropped. This problem started out on the starboard engine, but gradually the port engine developed the same problem.

Although I purchase my fuel from the same location as my friend, I always keep my tanks full, and to date I have not had any issues (knock on wood) My friend always kept his less than full, which I believe allowed moisture to form in his tank from condensation and has caused the issues he is having now. Food for thought.
Click to expand...

This could also be the issue. We have not been boating much because our son in his second year was jsut in a stage where it was difficult with him on a boat. Last year when he could not yet walk it was fine and it will eb a full season again next year.

Anyway, our tanks were full and with the same fuel since June and all summer. I had each tank treated with one quart of Stabil.

So sfergson ... did your friends issue clear up when he filled the tanks with clean fuel??
 
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Now I am beginning to think that the genny issue is cause by the same bad gas. A carbureted engine would probably be even more affected by bad gas than a forced FI engine.

I ran her 30 miles yesterday and I an down to a quarter tank. I will run it down to empty next weekend.

The question now is what fuel stabilizer to add? I had plenty of Stabil in the tanks all year and that did not prevent the issue.
Stabil is maing a new blue treatment that is especially for ethanol treated fuels, but it is not readily available. Need to try to get my hands on some of that stuff.
 
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I ran through 9 or 10 tankfuls this season and the issue was still there. I don't think I ever went more than 2 weeks with the same fuel in the tanks before needing to refill until recently. The last time I remember it, I had filled the tanks for a 3 hr cruise. About an hour into it, RPM's dropped. I guess the real test as to whether or not it was electrical for me will be the next time I finally get back out on the water. I have a half tank in it now and have not run the boat since the first of Sept. other than idling at the dock. My wifes shedule at work has kept her from getting to the boat and I'm to chicken shyatte to try to take it out myself (actually, dock it myself)

I can see how many of the lake boaters can have fuel related issues with the ethanol. I can't imagine you guys go through nearly as much as those of us in coastal areas with more places to go. I have burned 200 gallons in one day in the open water, can't even think of a way to do so in a lake other than the great northern ones. SB
 
Well, at least I have a bit of a game plan now with all the good suggestions from here.

We usually go through 1000 gal. a season, running about 40 miles every weekend. This season it will only be 300 gal.
 
Newbie.
I dont want to freak u out but i had 03 340. IT turned out there was a rubber glove left in the port fuel tank . as the rubber broke down it clogged the pick up. Never made it to the fuel filter. Just another thing to make ur head explode. Try running the boat off a temp fuel tank. Thats how we figured it out .


Rob
 
Robski97 said:
Newbie.
I dont want to freak u out but i had 03 340. IT turned out there was a rubber glove left in the port fuel tank . as the rubber broke down it clogged the pick up. Never made it to the fuel filter. Just another thing to make ur head explode. Try running the boat off a temp fuel tank. Thats how we figured it out .


Rob
Click to expand...
ROb ... how I.T.H. did you get it out of the tank??
 
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