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I have a 1993 omc 5.0 liter cobra that blows the circuit…

Customer Question
I have a 1993...

I have a 1993 omc 5.0 liter cobra that blows the circuit braker for the fuel pumps. the low pressure fuel pump gets very hot during operation, too hot to touch with your bare hand. I have changed the low pressure fuel pump twice and have replaced all of the components between the gas tank and the fuel pump, pick up tubes,anti-siphone valve,fuel lines, filter twice. I get one boating season out of the repairs and then it goes right back to blowing breakers and burning up the low pressure pump. The port side engine has been done 3 times and the starboard engine twice. Any ideas?

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Submitted: 25 days ago.Category: Boat
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Answered in 16 hours by:
5/28/2018
Marine Mechanic: Joe, Marine Mechanic replied 25 days ago
Joe
Joe, Marine Mechanic
Category: Boat
Satisfied Customers: 7,429
Experience: ASE, electronics, Marine mechanical and electronics, pwc, wiring, all around repair tech,
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Hello,

Thank you for allowing me to assist you, my name is Joe and I will be happy to help you with your concern today.

One thing I see here is that both engines are suffering from the exact same problem which usually indicates something shared between them, in this gas I am assuming you have a single fuel tank and or they both run from the same tank, correct? Has the inside of the tank been inspected? And how does the fuel/water separator look inside once this starts to happen?

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Customer reply replied 25 days ago
I have taken fuel samples from the tank and checked for water. The gas looked and smelled fine. I have replaced the fuel filters/water separaters several times, no water was present in the filers.
Marine Mechanic: Joe, Marine Mechanic replied 25 days ago

I am not really concerned with water, running hot for me would be lack of lubrication (fuel) but it could care less so long as it's liquid for cooling, so then I'd suspect if it were raw water cooled either lack of raw water cooling or lack of fuel. So then my thought was crud in tank or not picking up fuel or lack of raw water cooling if you have raw water cooled pumps?

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Customer reply replied 25 days ago
You are correct. I believe that it is a fuel/heat problem. The high pressure pumps which are water cooled seem to work just fine, the low pressure pumps have no water cooling and are the problem pumps.
Marine Mechanic: Joe, Marine Mechanic replied 25 days ago

Question, does this only happen when it is hot out? And or after running and then leaving out and going to restart?

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Marine Mechanic: Joe, Marine Mechanic replied 25 days ago

And what kind of engine bay/bilge ventilation are you using and are they moving enough air? Does it happen if the engine hatch is left open?

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Customer reply replied 25 days ago
It happens hot or cold, hatch open or closed, cold start or hot restart. Once the symptoms start ( surging at idle or stalling underway) the breaker will trip. Both high and low pressure pumps draw through the same 20 amp breaker.
Marine Mechanic: Joe, Marine Mechanic replied 25 days ago

What is the model number of your engines?

Have you checked fuel pressure during the problem?

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Customer reply replied 25 days ago
The staboard side is OMC model 50FAPRJVB the port side is OMC model 50 FAPLJVN. I am guessing that the pressures drop to near zero because the engine starves for gas but I could be wrong.
Marine Mechanic: Joe, Marine Mechanic replied 25 days ago

Correct and that's what we would need to know in order to diagnose the problem, need to see if it is a fuel loss problem or cooling problem.

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Customer reply replied 25 days ago
OK but I cannot get you an answer anytime soon. I’ll let you know what I find out as soon as. Thanks
Marine Mechanic: Joe, Marine Mechanic replied 25 days ago

Otherwise we are guessing as to which it may or may not be which won't help you much as if we guess wrong you'll just be checking things that don't matter, that;s why it is important to see where the problem lays first.

Thanks,

Joe

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