Where do I go from here? Melted spark plug

[D_J_Winn]

I have a 1997 MerCruiser 5.7LX (OKO26695) Bravo 3. I have been experiencing slow starts, rough idle, backfires at 40k rpm and can only achieve 41k rpm WOT.... as opposed to 47k. Today i dove into the engine and to my surprise i found #2 cylinder spark plug melted away after the threads. All others are fine. Looking for help in regards where do i go from here? Can anyone point me in the right direction, have any other ideas or suggestions? Thank You in advance.

Planing on pressure testing, installing a new distri. cap, and installing a new fuel pump. (things i have been wanting to do)

Not sure if this has anything to do with it, but i did have manifold and risers installed last yr.

 

[PS94]

Re: Where do I go from here? Melted spark plug

burning too lean/hot(bad intake gasket), detonation, rusted away, steam erosion? Got access to a boro-scope?

 

[Capt Ken]

Re: Where do I go from here? Melted spark plug

Possible intake leak causing a lean burn in that cylinder.

 

[achris]

Re: Where do I go from here? Melted spark plug

I have a 1997 MerCruiser 5.7LX (OKO26695) Bravo 3. I have been experiencing slow starts, rough idle, backfires at 40k rpm and can only achieve 41k rpm WOT.... as opposed to 47k. Today i dove into the engine and to my surprise i found #2 cylinder spark plug melted away after the threads. All others are fine. Looking for help in regards where do i go from here? Can anyone point me in the right direction, have any other ideas or suggestions? Thank You in advance.

Planing on pressure testing, installing a new distri. cap, and installing a new fuel pump. (things i have been wanting to do)

Not sure if this has anything to do with it, but i did have manifold and risers installed last yr.

Burnt plug, 40,000 revs... Not surprised!!!

Jokes aside. Very first thing, check compressions. Then check your timing, and that includes the timing advance. Also check your leads. A bad lead can cause a burnt plug too...

Chris.......

 

[makonnen]

Re: Where do I go from here? Melted spark plug

Could it be possible your engine swallowed something and it beat the crap out of the plug? Ie: swallowed a wingnut or something like that?

 

[gm280]

Re: Where do I go from here? Melted spark plug

Could it be possible your engine swallowed something and it beat the crap out of the plug? Ie: swallowed a wingnut or something like that?

Not saying that couldn't have happened, but a wingnut would mean both the intake and exhaust valves would have to open up really wide to allow such to get through...

 

[Bondo]

Re: Where do I go from here? Melted spark plug

I have a 1997 MerCruiser 5.7LX (OKO26695) Bravo 3. I have been experiencing slow starts, rough idle, backfires at 40k rpm and can only achieve 41k rpm WOT.... as opposed to 47k. Today i dove into the engine and to my surprise i found #2 cylinder spark plug melted away after the threads. All others are fine. Looking for help in regards where do i go from here? Can anyone point me in the right direction, have any other ideas or suggestions? Thank You in advance.

Planing on pressure testing, installing a new distri. cap, and installing a new fuel pump. (things i have been wanting to do)

Not sure if this has anything to do with it, but i did have manifold and risers installed last yr.

Ayuh,.... The most common cause of Detonation in a boat is bad gas, dirty gas, 'n plugged filters...
'n yer problem sure looks, 'n sounds like Detonation,...

Don't keep pushin' it, when it does it, or it'll be a Hole in a piston next time....
Probably got a good start on a hole now...

Inspect the contents of the fuel filter, insteada just throwin' it away,...

I'd Test the fuel pump, insteada just puttin' on a new 1,...

 

[Speakrdude]

Re: Where do I go from here? Melted spark plug

Was the spark plug "loose" when you removed? I have had that happen before. The loose plug causes a lean condition on that cylinder and will melt that sucker every time.
I will usually "tulip" the Intake valve too.

 

[D_J_Winn]

Re: Where do I go from here? Melted spark plug

Thanks guys for the help-
Unfortunately I wont have time until next Wednesday to work on her, but I'll be sure to update what i find.

Speakrdude- Not sure if it was loose (i can only hope) due to the threads being melted on the spark it was pretty hard to remove...might have to re-tap