www.iFourWinns.com

So I have been trying to diagnose my engine issue with no luck so far. I had written on this forum in the winter saying my motor would lose all power above like 25 mph. It would not make any weird noises, it would just power down. It may be starving for gas. I got a few replies and everyone said high pressure fuel pump.

My motor is a '93 OMC 5.0 EFI.

So I proceeded to do a fuel pressure test and it seemed to pass coming in right at 40 PSI.

From there I did a fuel pressure valve seat test and it seemed to pass again by maintaining pressure after I pressurized system.

From there I did a fuel pressure regulator diaphragm test and it passed again showing no fuel in the vacuum line.

I ran my codes and found code #63 - "throttle position sensor circuit below minimum voltage" new TPS installed.

Another thing I noticed is that my low pressure fuel pump is "warm" and my high pressure pump is "cool" What could this mean? Is my low pressure working hard and high pressure not working enough? Vice versa? IDK!

I am running out of diagnostic tests I can do myself, what else can I do to try to find my issue? (P.S. I'm not very skilled in this stuff, I borrowed a few tools and am just trying to follow my Seloc book)

Need Advice!!!!!

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1993 Sundowner 215
OMC Cobra 5.0 EFI
South Hadley, MA
Connecticut River Rat for life

Replaced the anti siphon valve on the top of the gas tank, it's the fitting that the fuel line to the fuel pump attaches to; make sure the tank vent is not restricted; remove the cover for the sending unit look in the tank to see if there is junk floating around in there.

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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

Thanks LouC, I'll try that next.

Would this explain my low pressure fuel pump being warm?

When I bought the boat 4 years ago I took the whole tank out and power washed it inside and out. Squeeky clean. I hope nothing is floating but i'll take a look.

After doing some reading and watching YouTube videos I am also going to try to take off my Air bypass valve and solenoid and clean that out. I heard this improves the idle "surge monster" I have that is an epidemic in Ford motors of the low to mid-90's.

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1993 Sundowner 215
OMC Cobra 5.0 EFI
South Hadley, MA
Connecticut River Rat for life

So I took the boat out for the first time this weekend...

She ran like a champ. I took out the anti-syphon valve and replaced it. The old valve had some stuff in it like a small dead spider and a few very small pieces of grass or something. Also, the spring that controlled the ball was tired. I'm guessing that the fuel pump may have been sucking the ball too far and therefore clogging the valve. IDK. Either way I got slightly above 40 mph without pinning it all the way to the "floor". I'm hoping this was not a fluke and finally got it running good. I'm glad I replaced the $10 valve before I bought $200-$300 worth of new fuel pumps.

Next project... Gauges!

P.S. LouC saves the day again. Thanks Lou!

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1993 Sundowner 215
OMC Cobra 5.0 EFI
South Hadley, MA
Connecticut River Rat for life

Sounds great keep us posted, love it when its a simple fix.....

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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

Hello again to All and Lou,

So I thought my original problem may have been fixed with the replacing of the anti-syphon valve, and it might have but she still isn't running great.

My motor now seems to have a skip in it. It mostly occurs at lower speeds or RMP but it has also happened a few times while on plane. It is a very quick skip or loos of power. I do have an OBD-1 code reader. Would this symptom cause a code to pop up?

The spark plugs are 2.5 years old now. Is there any reason to think it may be faulty spark plug wires? I don't want to throw $70- $80 bucks at wires and have it be something else.

Any comments? Advice would be great!

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1993 Sundowner 215
OMC Cobra 5.0 EFI
South Hadley, MA
Connecticut River Rat for life

Wires you can check the resistance with an Ohmmeter, look up the specs in the manual.
Plugs for sure I'd check them, the color of the insulator around the center electrode will tell you a lot. Brown/Grey OK, black fouled (oil or fuel) blistered white too lean. Black/White can cause mis firing. How is the dist cap, any cracks, carbon tracking, worn contacts inside?
I replace my plugs, cap and rotor every other season. Salt water corrodes the contacts inside the cap and plugs, well in salt water if you leave anything in too long, it ain't coming out easy.

A skip like that might not set a code. If it gets really bad it should set a misfire code.
You can tell much sooner by taking out all the plugs, take pix and post them up here. Measure the plug wire resistance, look for burned terminals on either end of the wire, check the cap like I said. No reason to replace plug wires unless they have high resistance, or burned contacts. The cap, rotor and plugs are wear items.

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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

For what it's worth, I've done my cap/rotor plugs and wires twice on my '07 to resolve issues. I believe it's been the same spark plug wire (#5 I think) on both occasions.

I keep my Rinda code reader in the boat to help check these things that crop up. I've also used it as a back-up when my temp gage started rising.... Though I was in trouble so started heading back before I plugged in the reader and placed in "live" mode. Used it the whole day like that! $400 well spent!

http://www.rinda.com/marine/marinemenu.htm

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Walt B
"Debt-Charged"
Black '07 H210SS
6.2L Bravo One turning a 21P HIFive
Wakeboard Tower with Perfect Pass Stargazer version
Missouri River; Kansas City, Mo.

Well, Hat's off to you for having accomplished all of this already.

Lou's advice is very good, but I would add that I would replace the distributor cap even if it "Looks" good. The cap can get some carbon tracking inside that's hard to see. Might as well change the rotor at the same time since it doesn't cost much. Then plugs if you have any doubts about them. On my previous 1987 OMC, that's all that I ever needed to fix a misfire. I probably did Cap/Rotor/Plugs every 3 years.

EDIT: Let me add that on my 1987 OMC, I also had Points and Condensor to change every three years or so. And the Coil seemed to last about 10 years.

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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

X2, and the dizzy cap can actually crack too. If it's bad enough you can see a light show at night.

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1987 Sundowner 195, 4.3 OMC " Z boat"
1983 Wellcraft 248 Sportsman, 3.0L OMC Sea Drive "Born Again"
9' Patriot 40lbs TM "Quack Addict"