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Yes I did remove oil cap - no smoke there. Did not check timing old fashion but will it work if PCM controls timing and shows already -3 deg at idle? Broken valve spring - don't think so compression 180psi each cylinder. I will definitely remove intake and check valve springs and clean...

Tried that while ago no leaks. Sprayed everywhere around intake and injectors. And this PCM wont change rpm even if sprayed engine starter into throttle body - tested to see reaction. Noticed only fuel consumption going gown immediately on vessel view. Checked also with smoke generator no leaks.

There's only the potmeter on shift plate and it sends signal to PCM and PCM controls the throttle body (drive by wire). Is that what you asked for ?

@muc what do you think of oil pressure? Only min oil pressure is specified in service manual 41kPa, mine is 280 at idle and 330 at 3000rpm. I'm just wondering if excessive oil pressure could be causing hydraulic lifter pump-up which in turn keeps the valves slightly open preventing the engine...

Fuel quality causing low intake vacuum? Its 95 octane exactly name E10. Spark plugs are correct.

Not sure because nothing showed up on Diacom. Guessing low water pressure

Can we now all agree that low vacuum is what I should be sorting out first? Today checked intake manifold with smoke generator. No leaks Any other ideas what to check?

@muc I also checked fuel supply module and it works nearly as it sholud. 1st video - ignition on the pressure goes up to 51psi. Then at idle stays steady 46psi. According to manual it should be 40-45. Its 1psi above acceptable range because its regulated by vacuum pressure and if this is too low...

@muc please see the attached Diacom recordings. The engine stopped due to an alarm, so the log is split into two files. Hope this is sufficient.

No way I thought its gonna be easier than that. Is it any other way to verify timing chain? IDK maybe measurement of valves and piston movement? I will run Diacom tests today. Vacuum stays at 12.5"Hg reading on gauge with engine warm up that's I'm sure and I think I should focus on sorting...

@muc Checked manual and 45psi is correct fuel pressure for that engine.

Props - turning point 14.25x21 and I thought that boat was sluggish because of that and replaced with SS 14.5x19. As long i won't see correct vacuum pressure I will be barking under that tree 😉

@muc when it comes to drive im pretty sure with correct ratio. I checked online Bayliner VR5 performance done by boating magazines and at 3000rpm and 4000rpm a get exactly the same speed as they did during boat test. If prop or gear ratio was different than what they had in test boat speed won't...

I will take engine photo tomorrow. It's version with only one O2 sensor per exhaust. I was getting confused with that mercruiser site with parts too. Its not very clear there with serial numbers etc. That sticker tells you all about catalyst - not for sale in California.

I know what diacom shows in regards to MAP explained it to someone just like you did few days ago under post #18. During Diacom test vacuum gauge was connected to manifold and never showed more than 12.5" on idle. BTW see attached. It's below 13"

It's alpha one gen 2. 1.62 ratio if I rememeber right

Found screen shot from month ago and water pressure was much higher. It all changed that one day. Engine keeps right temperature maybe just pressure sensor is restricted. I would expect overheating if watter pressure is 1/5 of what it was few weeks ago.

I will do it again tomorrow then and get some decent data. When I did the recording you just reviewed noticed that engine was warmed up, got on plane waited for O2 status to change to closed loop and I was sure that it was the whole PID ongoing. What else to look for to be sure that its in...

@muc please see attached the recording of my previous checks. Idle, then steady plane at 3000, 4000 and WOT

Do you know what was wrong with it back then? Was it repaired before auction or sold as it was?