1996 5.7 2 barrel suddenly idling high with black smoke out of exhaust

mtb_prodigy

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May 2, 2017
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I took her out to sea yesterday and was too tired to flush the engine. Woke up to do it this morning and I noticed I had left the gas cap open and it had rained a little bit. I topped off the tank last night. While flushing it started right up, was at 800 rpms for 10-12 seconds and then the idle started climbing all the way up to 1800 rpms. It steadily climbed to 1800 in about 40 seconds before I shut it off. I noticed black smoke out of the exhaust although that went away once it was at higher rpms. I tried again with the throttle cables disconnected but nothing changed. The engine also dieseled a few times for the first time yesterday. once for 3 seconds, once for 10, and another for 2 seconds. When I got back to shore it turned off properly. Im lost
 

achris

More fish than mountain goat
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May 19, 2004
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... and I noticed I had left the gas cap open and it had rained a little bit....

There's your answer... Water is heavier than petrol, it sinks, to the bottom of the tank. Where does the pick up sit what to get all the petrol out of the tank? At the bottom. So, until you used it all up, you had a di-hydrogen monoxide injected engine. That explains the increased idle speed, the dieseling, and the black smoke.

Pull your fuel filter. I bet it's full of the wet stuff...

Chris............
 

Bt Doctur

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Aug 29, 2004
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Never knew that stuff could be that bad for the enviroment
Dihydrogen monoxide:
  • is also known as hydroxyl acid, and is the major component of acid rain.
  • contributes to the "greenhouse effect".
  • may cause severe burns.
  • contributes to the erosion of our natural landscape.
  • accelerates corrosion and rusting of many metals.
  • may cause electrical failures and decreased effectiveness of automobile brakes.
  • has been found in excised tumors of terminal cancer patients.
Despite the danger, dihydrogen monoxide is often used:
  • as an industrial solvent and coolant.
  • in nuclear power plants.
  • in the production of styrofoam.
  • as a fire retardant.
  • in many forms of cruel animal research.
  • in the distribution of pesticides. Even after washing, produce remains contaminated by this chemical.
  • as an additive in certain "junk-foods" and other food products.

 

mtb_prodigy

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There's your answer... Water is heavier than petrol, it sinks, to the bottom of the tank. Where does the pick up sit what to get all the petrol out of the tank? At the bottom. So, until you used it all up, you had a di-hydrogen monoxide injected engine. That explains the increased idle speed, the dieseling, and the black smoke.

Pull your fuel filter. I bet it's full of the wet stuff...

Chris............


The dieseling occurred before I left the gas cap open. I'll take a look at the fuel filter

Is it dangerous to run it with water in the tank. I doubt it's very much.
 

achris

More fish than mountain goat
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...Is it dangerous to run it with water in the tank. I doubt it's very much.

Doesn't need to be much. The water washes the oil off the cylinder walls and leaves the pistons running up and down with no lubrication. I have only just rebuilt an engine that suffered from exactly that malady. And it was only about a cup of water in the tank....

Chris..............
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Also check the clear vent line from fuel tank to carb/spark arrestor. If it has fuel in it, your fuel pump failed.

Dihydrogen Monoxide is also one of the ingredients in coffee
 

achris

More fish than mountain goat
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....Dihydrogen Monoxide is also one of the ingredients in coffee
It's also used as an industrial cleaner. :eek:

And yet, with all those problems, governments aren't looking into it with a view to banning it. Makes you wonder what backroom deals have been done!
 
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Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Thats because people in government suffer from lack of nitrogen dioxide to their brains
 

mtb_prodigy

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Doesn't need to be much. The water washes the oil off the cylinder walls and leaves the pistons running up and down with no lubrication. I have only just rebuilt an engine that suffered from exactly that malady. And it was only about a cup of water in the tank....

Chris..............


If I syphon it out, will just removing 1/6 of the tank be enough since the water collects at the bottom? The tank is full I don't know where I'd even put all the gas if I pulled it all out. Wouldn't the fuel/water separator be capable of filtering out a cup?
 

achris

More fish than mountain goat
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Tip the front of the boat up. Start removing the petrol until it's not water. . You're done. The other option is toss in a bottle of meths.
 
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