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5 of 6 cylinders firing

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BSC Dad

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Any and all help would be greatly appreciated! Have a 1998 Bayliner Capri LS 1850 with the 4.3L Mecruiser. Boat starts fine but runs rough. Rebuilt carb then replaced plugs, plugwires, rotor button and distributor cap. Checked fuel from tank, its clean. Did a compression test, 5 of 6 cylinders 140ish one cylinder is 170ish, it is also the cylinder not operating properly. The reason I know this is because I can pull plugwires one at a time and this plugwire makes no difference in idle of engine. Ran boat anyway, ran good for 5 of 6 cylinders. Seemed to loose more power the longer I ran. Started a slight backfire/ slight pop from carb. Pulled plug from said cylinder and it was very nasty with what looked like oil with water in it. Pulled oil stick and it looks like oil was just poured out of can, brand new. Ran again on muffs in driveway no sign of oil in water from discharge, even after drying on concrete no signs of anything. Also no sign of moisture on oil filler cap. Again any and all advise where to look now or what to check next would be greatly appreciated.

I'm leaning toward pulling valve cover to see if there might be an exhaust valve issue. Wondering if this could be a head gasket issue or maybe I'm getting water in this one cylinder from the exhaust manifold?

Thanks, David
 
Yah could be a bad lifter, busted rocker, loose rocker, bent valve (prolly not), bent pushrod,...a lot to check. The fact that the compression is there is good sign. Should be ez fix.
I may be wrong but if it were head gasket the compression would be down I should think.
 
I would not rule out a bad wire... or a damaged/distorted contact at either the disti end of the wire or the plug end.... or for that matter, a bad plug.
 
sandkicker said:
I would not rule out a bad wire... or a damaged/distorted contact at either the disti end of the wire or the plug end.... or for that matter, a bad plug.
Click to expand...

Plug is new, plug wire is new, I have verified it firing up to plug. Neither of these would result in the water in the cylinder. That's where I'm really confused.
 
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