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No compression on cylinder no 6 on 2 Merc inboards

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quadraboats

New member
"Hi All, a quick google search

"Hi All, a quick google search pointed me in your direction so hopefully you can help me out with a problem im having with two Mercruiser engines.

Both boats have developed missfiring issues under load and at high revs. After some investigation i have found that there is no compression atall in cylinder 6 on both engines. Any ideas !?

One engine is a 2003 Merc 5.0 MPI and the other is a Merc 350 Mag 5.7. Am i missing something simple here !?"
 
The infamous #6
More than lik

The infamous #6
More than likely you will find a "tuliped" valve or a hole in the piston from a very lean fuel mixture
 
"Hmm, doesnt sound to promisin

"Hmm, doesnt sound to promising. Any ways of testing for sure before i start ripping rocker covers and heads off ?

Also would you mind explaining two things for me. What do you mean by tuliped and what would the most likely cause for the fuel being to lean ?

Thanks for the speedy reply !"
 
"You did compression testing a

"You did compression testing and got a "0" - not good. Leakdown test will enable you to refine the source of the problem. the top end will have to come off either way, so....get the compressor and the impact tools"
 
"Its home time for me now, bee

"Its home time for me now, been in work for 8 hours on my day off !

Leakdown test will be the first thing on the books for Monday morning. It hasnt been a good week atall, two blown Mercruisers in the matter of days, bah.

Any ideas why the fuel would have been too lean on both motors ?"
 
Tuliped valve is just like the

Tuliped valve is just like the flower looks.

If the plugs are off white to white; the combustion is burning too lean. You want the plugs to be a tan to medium brown color for optimum combustion.

Lean MPI may be an injector issue.

Lean carb may be wrong jets or poor fuel delivery.
 
"[b]"Any ideas why the fue

""Any ideas why the fuel would have been too lean on both motors ?"

Ayuh,... Hard to say,.. Could be as simple as Dirty Fuel Filters...."
 
"Afternoon guys.

Finally go

"Afternoon guys.

Finally got the heads of both engines. It looks like i have tuliped valves on both, cylinder 6 as expected. Ive got all the parts ordered to rebuild the engines but I'm a bit worried that this may happen again.

Both engines haven't long had new fuel filters, I've tested both pumps and they are ok, and i am sending both sets of injectors to be ultra sonicly cleaned.

Any thing else i need to check ?"
 
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