Mercruise 3.0 dieseling, no top end power

[Boater1981]

I finally got my Sylvan in the water this weekend after a $600 service bill. I put it in the water, it fires up and sounds good at idle. I give the boat some throttle and starts to make a load clattering sound similar to a diesel engine. The motor had no power beyond 2000 rpm and the last 1/4 throttle had no effect on power. I checked the plug wire configuration, made sure it had good fuel, cleaned the spark arrestor, spray cleaned the carb, tried messing with the timing (back yard mechanic next door gave me a hand). But at the end of the day it only made it worse.

When the engine is cold it would idle good but as it was revved up and brought back down it would start dieseling at idle.

Any ideas out there?

Thanks,

 

[JustJason]

Re: Mercruise 3.0 dieseling, no top end power

what's your oil level look like?

 

[Boater1981]

Re: Mercruise 3.0 dieseling, no top end power

Just changed at the marina and I checked it before I set the boat loose and it was all good.

 

[robjen1019]

Re: Mercruise 3.0 dieseling, no top end power

check your timing

 

[Doernuth]

Re: Mercruise 3.0 dieseling, no top end power

You didn't mention what the repair was? This could make a difference..

I would guess an ignition issue. Are the plugs fouled? What do they look like? Do you have a bad wire? Dist Cap?

Due to the issue that it idles ok, but wont run at higher rpms it could be an advance issue. Is it mechanical, vacume or electrical advance?

 

[Don S]

Re: Mercruise 3.0 dieseling, no top end power

The first you need to do is state what year it is and what ignition system. IF you have the EST distributor, "Messing with it" will really mess things up unless you had it in base timing mode.
You also need to do a compression test. Some 3.0L engines had problems with head gaskets blowing due to timing issues.
And don't go looking for a vacuum advance, the 3.0L never used one.

 

[Sweet sadie]

My 3.0 mercruiser seams to be in a nine since reinstalling