2006 Optimax 225 HP

[steve123]

The engine has 98 psi in 5 cylinders and number 6 has 76psi. The engine runs great. What could be wrong? Thanks!!

[flabum1017]

Could be a number of things with a 14 year old engine. Maybe a fuel injector ran rich glazing the cylinder, maybe an injector made it run lean and scuffed the cylinder walls, maybe it over heated one time, Maybe a head O-ring breached, maybe it got water in it, maybe it got reduced oiling...........................

[InjectorService]

You could check the direct injector teflon seal. Because they are installed in the cylinder head directly into the combustion chamber, if they leak you will loose compression. The above options are more likely though.

[billybob]

On any optimax engine. The first place to start, is quikcleen. You can shock it, which means putting a strong dose in small amount of fuel. take it out & run it about 3,500 rpm for a half hour. Alot of times these motors will carbon up, when you have debris in thermo,s causing motor to run to cool at low rpm,s & making it run too rich. It will normally set a code, thermo fault. Too many times I have seen people screw up spark plug threads, on #6 cyl. just by trying to change plugs. If powerhead has ever been off, it is possible, someone overtightened mount nuts & distorted #6 cyl.

[Motv18]

Another problem for 5-6 is the pulse pump tube leaking air.

Water from the air side can also throw a tench in stuff in high humidity and pea soup areas.

but without a bore scope (29.99 Home Depot) we can guess all day

#6 is normally the first to go on just about any v6 merc so I could just be that time.

Pull the kill switch and try again warmed up and oiled. If the kill wasn’t off you might have caught the air side back filling. That will give low numbers and high numbers if you crank and have the air side fire wince full.