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2004 Sunsetter running rough


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My 2004 Sunsetter LXi is missing at idle and has sluggish acceleration. 5.7 liter 320 Hp

It started running rough at the end of last season and has gotten worse this year. Misses at idle and during hole shot it feels like it is stumbling and weak. Occasionally it with recover and accelerate strong. Also when just crusing it will sometimes jump 300 rpms like the power comes back. Ran WOT and got 4400 rpms then the next time I only got 3900 with just me in the boat.

I have replaced spark plugs, cap and rotor...no help.

Just replaced inline fuel filter (under floor behind engine compartment )....no help. Is there any other fuel filter or screen on the fuel system?

Thanks

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Fuel pump maybe? I don't any skill to base that on though. You can test the fuel pressure at idle and WOT (on the lake) by borrowing a fuel pressure tester from many local auto parts stores. The fuel rail has a spot to connect it. I forget the numbers though.

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The pressure was tested and I was told it was good, but they did not take it to the lake so I assume that it was either taken at idle or maybe just at "key on". I don't know what that value was however.

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There is a screen on the inlet of the fuel pump. Mine was partially blocked when I had fuel problems. Very easy to chekc just by removing the hose and shining a torch into the pump.

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There is a screen on the inlet of the fuel pump. Mine was partially blocked when I had fuel problems. Very easy to chekc just by removing the hose and shining a torch into the pump.

LOL careful all you members in the USA. Our friend Down Under is referring to a flash light when he says "torch". Just had this great image in my mind of someone getting down there with a butane torch!

  • Like 2
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Also I forgot, since this is fuel injected, maybe one or more injectors is not working as good as it should?

Check the fuel pressure at WOT, bakes chart says 58-62 psi at WOT for a 2004, sounds like either a fuel pressure problem or your injectors need cleaning or both.

http://www.bakesonline.com/images/MediaLibrary/Indmar_96-06FuelpsiRef.pdf

Edited by Bozboat
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An inductive timing light or spark tested should show if a current cylinder is not getting fire properly. Hold the inductive pickup onto each plug wire close to the plug and the light should flash each time the plug recieves fire. You can do this at idle while it has the miss. If you done see a steady rate of flash on each wire, the one the flash is missing on is the problem cylinder. I'm not sure how to test injectors aside from removing each one. Maybe one of the spark plugs, if you pull them would show some evidence.

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I'll use a flashlight for now. If the problem can't be solved maybe a torch later! I was told that there is another filter by the pump (rear left side of engine)? Also a mechanic said there are screens on the injectors and idmar recommend they should just be removed? Does anyone know about that?

He also said its rare for wires to go bad....only 260 hours on boat. But I will replace or try to test.

Thanks.

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