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HELP--2001 Vista 328 with Volvo 5.7 SXI 280 hp. motors (fuel injected). The starboard engine loses power after @ 7 miles of running. I've done everything and had 2 of the best yards on Cape Cod in MA. look at it multiple times. Bought the boat used July 2013.
Now has 790 hours on each motor.
The boat had sat as an estate sale from July 2010 to April 2013
Yes, It passed my sea trials of @ 5mile run, with my surveyor on board (after the seller broker replaced the fuel pumps on both motors)
Here's what we've done

Fresh fuel
2 new fuel cell / pumps (on both starboard and port motors)
removed anti siphon valves on both tanks
Replaced fuel lines
replaced fuel filter multiple times
Swapped fuel pumps from starboard to port and back
Swapped engine computer / control module from starboard to port.

Thought we had it nailed last year when the starboard fuel tank sender was found to be bad and it was apparently out of fuel
Replaced the sender and it still happens
Ran both motors off both fuel tanks--still happens
Next to try is shut off the fuel from the starboard tank and run the starboard motor off the port tank

It acted up a lot last season
Then the last 2 trips of 16 miles each at the end of last season, it ran fine
Then the first trip of 16 miles 2 weeks ago, it ran fine
Then this weekend it was back to it's old ways. Ran @ 7 miles OK, then lost power in the starboard engine. Then when it happens I can run up to 2K rpm for about 1/2 mile, then it loses power again. If you keep it up, it will barely run at idle, just enough to keep the power steering.
Then on the second leg of the trip, 2 days later, it ran only @ 3 to 4 miles then lost power. Getting it back up on plane again after a few minutes of idle speed, it would only run 1/4 mile again.
No backfires, starts fine, no noises, no water in the oil.

If I didn't know better, I wonder if it could be a cracked intake manifold that the crack opens up under heat after a few miles? But then why would it get back to running OK?
Maybe a bad sensor somewhere?
I'll try more fuel and running the starboard motor off the port tank and see what happens--even have my shop contact Volvo I think.
Any ideas?

I am up in Boston and there is a place called McLellan Bro.in Everett 617 389 5508

I have heard great results from them! Even after the dealer looked at it.

What comes to my mind is the flap in the exhaust.

If you haven't already done this it might be a good idea to attach a fuel pressure gauge and see if there are any changes while it's happening. Any chance it's not fuel related and something is heating up in the ignition system like a coil or ignition control module and dropping out? Like you said it does sound like a sensor or something just dropping out or giving erratic signals once warm.

Another thing worth checking would be to back probe the injectors with a noid light and watch to see if it gets dim or starts dropping when you have problems....just thinking out loud here as you may have already done this stuff

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Our Boating Blog: http://ben-dana.blogspot.com/

2005 268 Vista "Sea Pickle II"
1979 AMF Alcort Puffer
Previous:
2003 FW190 Horizon
1973 Startcraft 18ft "Sea Pickle"

A couple of other things to look at are a dirty fuel pressure regulator and cleaning/testing your injectors. It seems that the paint from the fuel cells may clog those items as well.

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2004 Vista 298
Twin 5.7L Volvo Penta GXi-E

The shops have pretty much done all the basic fuel system work as you guys say. One shop (Hyannis Marine) even put a clear tube in the port line, said they say air bubbles in it, and gave it back to me as I needed to get the boat to my mooring on the Cape. Surprisingly enough it ran like a top from Hyannis to Martha's Vineyard even though they didn't know if they'd fixed it.

At the second yard, we put 50 gal of fuel in it after a lot of work such as switching the fuel pumps and engine modues from side to side and then finding a bad fuel sender -- it then ran fine for @ 3 trips of 16 mile each. The senders been replaced and it still shows @ 2/3 full of fuel but is acting up again of course.
This coming weekend I'll put another 50 gal. of fuel in the stbd. tank and see if that works, and try running the cranky stbd. motor on the port tank too. Maybe one or the other will give me some clues. Maybe I have "slow electricity" as they say up here and the gauges are still off due to a bad ground or other wiring issue or circuit breaker?
Any other thoughts anyone?

If you have air bubbles in the clear, then you have a leak somewhere. Here is a troubleshooting guide off of iBoats for fuel systems.

http://forums.iboats.com/forum/engine-r ... uel-system

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2004 Vista 298
Twin 5.7L Volvo Penta GXi-E

Well, another few weeks of the same issue. It ran fine two 16 mile round trips at the end of last season from Falmouth MA (on Cape Cod) across the channel to Oak Bluffs on Martha's Vineyard. Then ran fine for two more round trips the beginning of this season.
Now, the last 3 round trips on the last 3 weekends, the problem is back. It runs OK for about 3 to 4 miles and stbd engine loses rpm. Run it a few minutes at 1800 rpm, bring it back up on plane and it then runs only about 1 to 2 miles (depending on it's mood at the moment). Repeating this routine, it runs less and less on plane each time, until it will go only about half a mile on plane (about 3200 rpm or more).

I called Volvo Customer Relations for their tech guy and my shipyard has already called for him. Hopefully when he gets back from vacation next week we'll know something more. My yard is a Volvo approved too so that's good.

Will keep all of you posted when it's finally sorted out!

My Father in law has been battling this same situation with his pontoon for several years. He and I have replaced everything to do with the fuel system except for carbs. So this summer we rebuilt them and it seems to have cured the issue. Not sure if yours is a carbed setup or not but it is worth a shot.

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1990 Four Winns Horizon 200
2005 GMC Sierra