1999 21v Riders Edition issues

[COTige21V]

Ok wet compression test done and the 4 and 6 that were 60, #4 went up from 60 to 90 and #6 went from 60 to 100. Not sure what to think? Head gasket or stuck/sticky valves?. I am at a loss and would love to LS swap it lol

[COTige21V]

Ok I will do a leak down on it. Do you think it would be better to do it or to just get new heads and head gaskets?

[COTige21V]

But if it was ECM don't you think the computer would pick it up and show an error of some sort? It's strange to me too. Maybe buying a known good ecm would be smart. I will also see if I can borrow one. To verify. I got a really good deal on this boat so putting money to make it good is my goal. Make it as reliable on the lake. I have LS swapped a few vehicles and have been going through the process of getting a parts list for the swap. But this engine has low hours so it should last a while lol

Summer is getting short and it does kind of chap my *** that I didn't get as many days on the lake.

[boatwakes]

COTige, I have 2 pairs of ready to run Mercruiser 906 casting heads, gaskets and all the fixings ready to go if you need a set. The compression being low in 4 and 6 indicates you have a manifold to riser gasket leak on that side of the engine and water has been making its way to the exhaust valves (we see it all the time). Replace the exhaust when you do the heads, both manifold and risers to avoid this in the future. However, no spark on 2 and 3 indicates an ECM issue which is not terribly uncommon with the MEFI 3 system. Arizona speed and marine can possibly reprogram but a MEFI 4 upgrade may be the only available option if you can't find a known good MEFI 3 ECM.

[boatwakes]

If you're doing an LS I would strongly suggest just buying the stand alone from Marine Engine Depot, its a drop in marine engine with closed loop MPI compared to screwing around with "making it work" custom installation crap.

[COTige21V]

There is a part of me that wants to do the LS. I have a 5.3 that is 325hp but is going into a Land Rover... oh decisions. I think I would prefer a 6.0 or 6.2 and I will check out the Marine Engine Depot.

But this one with 502 hours (from the computer not dash, dash says 163 hours. But it is low hours. I am going to do the head gasket, ecm, deck the head and have it freshened up. If the cost is worth it to do both I will but thay other side is good. That way I can still use it while I source a 6.0 or 6.2.