5.0 mpi runs rough when wet

[woodguy81]

Can’t seem to track this down but noticed when the engine gets wet it runs rough. Low power, poor fuel mileage. Checked plugs, wires, cap and rotor replaced twice. Good fuel. Clean filter. When I left the engine cover off and let everything completely dry for a few days it was able to run 20 miles offshore without a hiccup. After being out all day and taking in some water through a new transducer wire hole I forgot to seal up, the motor ran like garbage again. What else would likely cause this only when it’s wet. Also probably near the bottom of the motor as the water that came in would have splashed up from there. Any thoughts?

 

[Fun Times]

What year is the boat engine? Engine serial number handy?
What area seems to be getting the wettest?
Distributor assembly maybe?
Is there high humidity in the area while running, etc.?

 

[tpenfield]

Hard to imagine that much water getting in unless you had 6-8" of water in the bilge.

If so, then perhaps the electrical wiring is getting wet and reducing the voltage to the engine.

 

[dubs283]

Can’t seem to track this down but noticed when the engine gets wet it runs rough.....After being out all day and taking in some water through a new transducer wire hole I forgot to seal up, the motor ran like garbage again. .....Any thoughts?

Although the design of the engine is to be operated near water it isn't designed to be operated when doused with water. Your issue could be one or more things but first you should locate and repair the water leak(s), then check operation when the engine is allowed to operate without being wet

 

[Lou C]

Check your spark plug wires & distributor cap, when the insulation gets old & dried out it can allow misfires to happen, make sure that you don’t have water spraying from a hose behind the engine on the distributor.
We had this on an older Subaru, when it got damp it would throw a misfire code & run rough, cured it by coating the plug boots on the coil with dielectric grease. Might try that first if the wires aren’t in bad shape.