www.iFourWinns.com

Hi

I had a backfire issue at WOT last season post purchase, however this was not present during the pre sale trial. Decided to give the boat a full service including all filters and plugs. Cleaned out the fuel tank and inspected the tank via the sender and ragged out to confirm clean. Dropped the boat in for her first run this year and hit the same issue at WOT. Boat runs fine just over 3000rpm and will run at 25 knots all day no issues. Open her up to WOT and within 30 seconds the power drops off and pop goes the weasel!!
Not sure if this is a fuel starvation issue or wiring/ECU issue? I have yet to check the fuel screens in the fuel pumps as I lack info to do the same.

I could do with a few pointers from anyone who may have had similar issues before I dive in?

Thanks

Mick

Volvo or Merc?

Engine is a Volvo 4.3l gxi

What did the plugs look like? Running lean? Then look for vacuum leaks and clogged fuel injectors. You might want to do a compression test to rule out sticking valves

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88 Four Winns 200 Horizon
4.3 OMC Cobra-4bbl
2002 Walker Bay 10/2012 Suzuki 2.5
2008 Walker Bay 8

1998 Jeep Grand Cherokee 4.0/Selectrac
2007 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

After dealing with paint issues in my fuel pump and fuel pressure regulator, I was getting backfiring. I had the injectors serviced which eliminated the problem.

https://www.injector.com/injector_service.html

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2004 Vista 298
Twin 5.7L Volvo Penta GXi-E

That is what i was thinking

+1 on fuel supply.

Mine was ok on half to 3/4 throttle up to about 3500rpm then stuttered and backfired over 4000rpm. Fuel pump replaced ( Motor out job for my boat) and all good now.
However on a previous boat the timing was not advancing sufficiently causing similar issues..

Check fuel pressure if you can on the water when it backfires, if fuel pressure is to spec it is timing.

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Cheers

Mark
Melbourne
Australia

Boats:
Current: 2004 FW 190
2001 Mastercraft X5
1998 Malibu Response
1999 Sea Ray 180
17 ft Scimitar Barefoot (200hp Yamaha)
16ft Scimitar Ski (Yamaha 115)
1988 Ski Nautique ( Called Ski Antique)

Ahhhh yes, where do I start?? I echo everybody else - this smacks of a fuel starvation issue. I know a lot about this, because I chased bad fuel pumps on BOTH of my twin 4.3Gi engines for 2 summers. Trust me - those fuel pumps might sound find when they prime, or when they are running; but they still can be under performing a great deal.

It took me 2 summers of throwing parts at the boat like crazy, Im sure my neighbors thought I was purposely trying to let the boat bankrupt me, seeing me go to the boat every day after work like clockwork with a new bag of parts from the Volvo Penta parts department, lol. I swore my fuel pumps were fine. One day there was nothing left to replace, so I went and bought a high pressure fuel pump for my stbd engine. Solved my problems. A month later, I replaced both the low and high pressure pumps on my port. The engines have never run better since, and all of my backfiring, popping, hard starting, stalling, and every other weird random intermittent problems I had went away.

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1997 Four Winns Vista 278
T - 4.3l EFI
Kohler 4esz Genset
379 hours as of 8/8/21

Good info on this issue.
The real question is why marine pumps seem to fail more often than automotive ones. Probably because auto pumps can be in the tank (cooled by gas) and push fuel instead of pulling it.
Meanwhile I still have the OE mechanical pump in my old boat.
Think of it this way, an EFI system needs much higher pressures all the time than a carb system. They have to maintain close to 40-50 psi at the fuel rail. A carb system only needs 5-6 psi because a carb works on vacuum not pressure like EFI. So all it needs is to keep the carb bowl full of fuel.

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88 Four Winns 200 Horizon
4.3 OMC Cobra-4bbl
2002 Walker Bay 10/2012 Suzuki 2.5
2008 Walker Bay 8

1998 Jeep Grand Cherokee 4.0/Selectrac
2007 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II

I had the timing issue when I first bought my FW. However a careful review of the symptoms might tell you which one you have.

For the timing issue:
Mine would run perfect up to about 85% power. Above that, it would backfire and not get any additional power. Mine also did not show up on the test ride, but in my case, I think it was caused by my switch over to 10% Ethanol gas (E10) instead of Marina gas that the previous owner used. I found that I had to advance the timing a few degrees to get it to run perfect on E10.

Fuel Pump or Fuel Filter issues:
If you momentarily get to near full power, but then it backs down (and backfires), then you likely have the fuel issue, not the timing issue. (Your description sounds like this one).

Ray

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"Knot Easy" 2000 Horizon 240 Volvo 5.7GS /SX
tow: 2017 Honda PILOT EXL-AWD
prev. boats:
'87 Chaparral 198CXL 4.3 OMC Cobra
'69 Jetstar 16ft Ski Boat, 115hp Yamaha
'68 Aluminum Jon Boat, 3hp Sears
'64 Water Wings

Dropped my boat in on Saturday, port engine is running like crap. Haven't dug into it yet but it sounds like fuel starvation again...

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2004 Vista 298
Twin 5.7L Volvo Penta GXi-E