www.iFourWinns.com

This started last month - my 278 Vista has twin 4.3Gi's (throttle body injection) with all symptoms of a high pressure fuel pump on its way out on the Starboard engine, Port engine runs excellent (please dont jinx me, lol). I changed the high pressure fuel pump, problem persisted. Changed the low pressure pump - problem persisted. Changed the ignition module in the distributor (HEI) - problem persisted. Engine has 370 hours on it. Cap and rotor look good, no corrosion or carbon tracking. Engine temps around 150f the entire time and strong oil pressure.

Problem: Engine starts great, idles smooth (maybe a little rich but how can you tell on an old school 4.3 with no feedback control!), planes out strong. After 5-7 minutes, I start to see my tachometer on that engine begin to go up and down a few hundred RPM's. If I try to give it gas, it falls flat on its face, almost stalling while on plane. If I leave it alone, the RPM's will dance from 0 to 3300 and basically just go all over the place. Twice, it has backfired through the intake when this occurs. I have to come off plane, but anything under 2800 RPM's it goes back to running SMOOTH as day, and powerful. I get back on plane (strong smooth), and it takes another 5 minutes to start the procedure all over again. I swear I heard one of the fuel pumps whining AFTER this happened a few times.

Ive changed: Low & high fuel pump, fuel filters, ignition module, and today I cleaned the anti-siphon valves which were FULL of plastic and what looked like insect legs/wings or something. The check ball was definitely obstructed. Still I am not convinced. It seems like a thermal issue to me (coil heating up, cutting out, ignition module heating up,cutting out, etc). Or am I overthinking this.. I called my mechanic and he said hes had a rash of bad Sierra caps & rotors lately, causing arcing and all kinds of problems. Coincidentally, I have Sierra on there (replaced 2 years ago with only like 30 hours on the parts). There was no corrosion or carbon tracking that I could see. Suggestions?

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

Well the hardest thing with these problems is always to narrow it down to ignition or fuel. For ignition I might hook up a timing light to #1 plug wire; observe it when it’s running well then observe when it’s running poorly, any difference in the frequency of flashing on the timing light?
For fuel system checks, run the engine at idle and then at about 2000 rpm in neutral with the flame arrestor off. Observe the spray pattern when it’s running ok then check again when it’s running poorly. Might want to take vids of both ignition and fuel system tests. This might help you narrow it down to which system is acting up under load. If you have aftermarket distributor caps I might change those to OE since that’s an easy fix.
PS I would dump out the fuel filter in a large mason jar and see what it looks like. Layer of water or crud on the bottom? Also I think you’re better off replacing the anti siphon valves with brass instead of aluminum ones. My mechanic did that 15 years ago for a similar problem and no problems since.

something else:
http://www.volvopentastore.com/Vapor-Se ... _id.776029

I'm really not familiar with these sysetms yet but I'm wondering about this, could there be debris in the vapor separating tank, or some other issue with it?

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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

Just to update and close this one out, my anti-siphon valves at the gas tank were COMPLETELY clogged. I couldnt even blow air through them! I do not know how the thing was even running at all to be honest. Took me about 20 minutes on each anti-siphon valve with a pick to get all the crap out. Lots of (what looked like) machining metal shavings, bug parts, string (have no idea on that one), red plastic shavings from 5 gallon gas cans of yesteryear (the boat was kept at my personal house at my seawall for ~8 years so thats how I filled it). Added checking/cleaning anti-siphon valves to my maintenance sheet!

tl;dr I replaced fuel pumps and fuel filter/water separators for nothing

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

thanks for the follow up, I was thinking that the anti siphons could still be the problem even after cleaning, they can get internally corroded and my boat had that exact probem years ago when we first bought it, my mechanics caught it. So now you have 2 spare fuel pumps, think of it that way!
BTW, there are better quality anti siphons made of brass I think less prone to corrosion like the aluminum ones are.
As far as spares, I have a ton of spare parts for the OMC Cobra system because you can't just go out and buy parts for them when you need it. Most will probably get sold when I sell the boat eventually but I'd rather have some extra clutter in the garage than have the boat sitting waiting for parts for weeks during the summer. Spares:
complete outdrive
complete transom mount
exhaust Y pipe
steering actuator & pump
carb & fuel pump
old style points distributor
Hoses, belts, etc.

_________________
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