Mercruiser 3.0 LX 1996 cylinder misfire

[Pcholmondeley]

Have a problem with idling after full power run looking for comments

Boat starts and idles well but after running at mid or high throttle for any any length of time {and by the way is runs very smooth at speed** return to neutral it runs rough and misses on #2 cylinder proven by removing lead. The plug is sparking well. Once engine is shut off for a few minutes it starts up smooth again running on all cylinders and will idle all day that way until it runs under power again.

What has been done -

New manifold
Rebuilt cylinder head
Valves adjusted but oddly can not run if set to factory procedure will only run with 1/8 nut turn after zero lash
New plugs
New distributor and rotor
timing, compression test and tune up done by certified merc mechanic
He has ruled out ignition and fuel issues I agree as all cylinders share fuel input
Spark plug color is fine on all cylinders even after misfiring

His conclusion is the #2 valves must be sticking when hot or slight water leak into cylinder !

I am not sure I agree as it runs so well under power.

Looking for any thoughts or suggestions before I dismantle

Thanks

Peter

 

[alldodge]

Re: Mercruiser 3.0 LX 1996 cylinder misfire

Have a problem with idling after full power run looking for comments

Boat starts and idles well but after running at mid or high throttle for any any length of time {and by the way is runs very smooth at speed** return to neutral it runs rough and misses on #2 cylinder proven by removing lead. The plug is sparking well. Once engine is shut off for a few minutes it starts up smooth again running on all cylinders and will idle all day that way until it runs under power again.

What has been done -

New manifold
Rebuilt cylinder head
Valves adjusted but oddly can not run if set to factory procedure will only run with 1/8 nut turn after zero lash
New plugs
New distributor and rotor
timing, compression test and tune up done by certified merc mechanic
He has ruled out ignition and fuel issues I agree as all cylinders share fuel input
Spark plug color is fine on all cylinders even after misfiring

His conclusion is the #2 valves must be sticking when hot or slight water leak into cylinder !

I am not sure I agree as it runs so well under power.

Looking for any thoughts or suggestions before I dismantle

Thanks

Peter

I'm thinking you have a collapsed lifter. Is the rocker nut appear to be turned in more then others (more thread showing)

 

[Pcholmondeley]

Re: Mercruiser 3.0 LX 1996 cylinder misfire

Thanks for the response, do you think the lifter would un collapse as the engine cools and run normally until run hard again ?

Peter

 

[Bondo]

Re: Mercruiser 3.0 LX 1996 cylinder misfire

Thanks for the response, do you think the lifter would un collapse as the engine cools and run normally until run hard again ?

Peter

Ayuh,.... Welcome Aboard,..... How are ya findin' 0 lash,..?? By rotatin', or push/ pullin' the push rods,..??

Go Run it, 'n when it starts Skippin',... Do a compression test on #2, 'n See,...

 

[alldodge]

Re: Mercruiser 3.0 LX 1996 cylinder misfire

Thanks for the response, do you think the lifter would un collapse as the engine cools and run normally until run hard again ?

Peter

My thought is that the engine heat increases at higher rpm as it should. There is probably a slight miss but nothing noticeable at the higher revs. Higher heat equals more expansion, the increased expansion tightens the nut more (not really but used for example only). As the engine cools expansion decreases and your running good again.

This is just my guess right now. Doing a compression test as Bondo mentions would add some needed info. Other info such as seeing if the rocker nut is lower then the rest. Another thing which may help decide the issue, is if more threads are showing, retighten the rock just to zero backlash and see if the symptoms go away. If zero lash does fix it then you need a new lifter

As before I'm just guessing, the compression test will help and you don't need to pull the valve cover