Mercruiser 5.0 loss of power

[pmeyers61]

I have a 2003 Mercruiser, 5.OL It has maybe a 200 hours on it. Raw water cooled, used in salt water. Rarely left in the water for more than a couple of days. Fresh water rinsed when hauled out. The boat was winterized by a mechanic last year.
When I put the boat it this year, it had some moisture in the distributer which causes it to lose power; easy fix. Spent one day fishing, no problem. The next day I took it out fishing, I got an intermittent backfire with a loss of power. I would drop it ino neutral, the engine would recover and I seemed to again have full power. This happened about a half a dozen times when the engine just lost power. I couldn't get the rpms up over 2500-3000 and the speed up over 8 knots. I assumed it mght be the distributer again, but when I opened the engine compartment, there was fresh oil in the bilge and there was smoke/back pressure coming from the hose that ran from the starboard valve cover to the carb. I came back on the kicker.
The oil pressure remained normal and the engine temp remained normal. Judging from the dipstick, it lost about a 1/2 quart of oil. There is a PCV valve on the port valve cover, I took it off and it rattled, seemed clear.

I am in a fairly remote area on Vancouver Island and am taking the boat to a mechanic in the next town about 40 minutes away tomorrow. His initial reaction on the phone was that it didn't sound good, suggesting that it may require some tear down. It would be extremely helpful for me to know in advance what type of diagnostics I should expect the mechanic to perform and based on what I have described is it possible to speculate on the potential problem(s)? I'm dumb as a stump when it comes to marine engines.

 

[mylesm260]

Re: Mercruiser 5.0 loss of power

Fresh oil in the bilge shoudn't be too hard to trace back.


I don't know why his initial reaction was tear-down, because you didn't mention any knocking sounds or anything that would indicate serious engine problems. And you said you still had oil presure.

My initial thought is something related to your PCV system (is your engine over-fillled with oil maybe?) Oil getting into your carb could certainly cause your engine to run like garbage (and explain the oil in your bildge if it was leaking somewhere as well)


I have a feeling he will have a quick diagnosis when he looks at it, like I said, there arn't very many ways for oil to escape from the engine (especially with only 200 hours on it)


Also, if your engine is EFI with electronic ignition, then you may have a trigger sensor in your distributer (below the cap and rotor area) if water got into there, it could certainly cause your backfiring.

Here's another thought: If you were backfiring through the intake (plug firing when your intake valve is open) then that would temporarily presurize your entire intake manifold, which would in turn put presure through your PCV system into your crank case which could have forced oil out somewhere (maybe even out the dipstick oppening).

Did you ever check your distributer the 2nd time?