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1994 Sport Nautique seems to be running very. Oil residue…

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1994 Sport Nautique seems...

1994 Sport Nautique seems to be running very rich. Oil residue coming out exhaust system and black smoke. Also charring spark plugs very badly

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I rebuilt the motor this winter. New block. Hooked it all back up, set the timing and the boat ran pretty well. But when I went to water test it at the lake it overheated instantly. Ended up being a bad impeller. That is fixed now but blowing lots of black smoke and oil residue out the exhaust. Something else to note, when hooked up to a hose the water tends to build up pressure and then surges out of the exhaust over few seconds. I don’t remember it doing that before. My first thought is that when the boat overheated that it maybe burned up the fiberglass muffler and maybe that is causing blockage and also causing it to run rich.

Submitted: 2 months ago.Category: Boat
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Answered in 4 minutes by:
5/30/2018
Marine Mechanic: Jason, Marine Mechanic replied 2 months ago
Jason
Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 18,187
Experience: Degree in Marine Technology. Gas and diesel marine mechanic.
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Hello my name is ***** ***** am I speaking with? I read what you wrote. Which engine is in your Nautique?

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Customer reply replied 2 months ago
Steve. 1994 351 Ford EFI PCM 5.8 pro boss motor
Marine Mechanic: Jason, Marine Mechanic replied 2 months ago

Got it. I generally do not work on those engines because there is no support for them any longer, but I have an idea of what is probably wrong. Are you able to compression test the engine, do you have the tools for that?

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Customer reply replied 2 months ago
I do have a compression tester but I’ve never done it’s. Seems fairly simple though
Marine Mechanic: Jason, Marine Mechanic replied 2 months ago

Just pull 1 plug out, stick the compression tester in, crank the engine over 4 or 5 revolutions, see what the gauge reads, put that plug back in and move on to the next cylinder. Can you check all 8 and let me know what your compression numbers are?

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Customer reply replied 2 months ago
Ok. I’ve actually done that but then another mechanic told me your supposed to pull all plugs to get the correct reading. Either way, when I tested it one by one, I got anywhere from 115 to 120 on every cylinder.
Marine Mechanic: Jason, Marine Mechanic replied 2 months ago

When did you test this, did you test it before it overheated and was blowing black smoke or did you test it after it overheating?

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Customer reply replied 2 months ago
I tested it after it overheated and after new impeller installed. I tested it because it was blowing the black smoke and oil residue.
Customer reply replied 2 months ago
Just for a little history’s too, before I rebuilt the motor I lways though it ran rich. It tended to foul pluggs and was really slow pulling skiers up and wouldn’t tend to blow out black smoke when I tried to pull up a skier. Just wanted you to know that in case it changes your thoughts on where the issue is.
Marine Mechanic: Jason, Marine Mechanic replied 2 months ago

My initial thought was that you had low compression, as that is what causes black smoke 90% of the time. Your compression is on the low side but I can't find a spec on it anyplace and I don't have the manual for this engine so I can't say for certain 1 way or the other if your numbers of 115 to 120 were to low. I will opt out and leave your questions open to the community. Good luck.

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Customer reply replied 2 months ago
I’ve found what seems to be the correct manual online at: http://www.planetnautique.com/CorrectCraftManuals/1993/93PCM.pdf
Marine Mechanic: Tan, MerCruiser Certified Technician replied 2 months ago
Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 11,415
Experience: 40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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Hello. My name is Tan.

Black smoke and fouled plugs can also be too rich. Have you checked your fuel pressure?

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Customer reply replied 2 months ago
Not yet. But I can do that ASAP
Marine Mechanic: Tan, MerCruiser Certified Technician replied 2 months ago

If the fuel pressure is above spec this will cause the black soot on the plugs. Spec. 31-39 psi.

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Customer reply replied 2 months ago
Would it also cause black soot to come out the exhaust? I have an excessive amount coming out now
Marine Mechanic: Tan, MerCruiser Certified Technician replied 2 months ago

Absolutely. The soot usually floats on the top of the water.

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Customer reply replied 2 months ago
Ya. Exactly.
Marine Mechanic: Tan, MerCruiser Certified Technician replied 2 months ago

High fuel pressure is due to a failing fuel pressure regulator.

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