Mystery Loss of RPM 496MAG
 

Gettng quickly to the point...2008 Twin 496MAG BIII with Livorsi Throttles and Smartcraft, 70 Hours on engine.

For 70 hours both engines ran pefect...meaning let's say at 40% throttle both RPM's were at 3300 RPM, with exact fuel burn in GPH.

Then one day in an instant...my STBD engine now requires 55% throttle to acheive the same RPM's and it now burns 2-3 GPH more fuel at the same RPM's.

By the way, inspection of outdrives and props was completed and no damage...so it must be engine related???

I've been researching and researching this thread...and I've gotten some ideas...but I want to make sure I cover everything. I am not a mechanic, but I can get around...so what I want to do is make sure I am covering all the obvious, before I start to pay a Merc tech.

Below are all the items I've found that need checked. The items in dark blue I can check myself...other than that I will have to go to a tech. Is there anything else I could check myself...or should check. Then if all fails, what should I have the Merc Tech do first? Assume a Engine Scan? Do you think my order is good?

By the way, I have buddy with same issues...he checked everything in blue, added new plugs, ran a scan test and nothign wrong...guess his next step is a compression test??

Spark Plug(s) Bad
Spark Wire Disconnected
Ground cable to battery loose
Fuel Filter
Too much oil
engine in Guardian mode

Engine Scan
Crankshaft position code activated
camshaft position code activated
Clear all engine codes
Compression test
Leak down test

Thanks in advance!

Nice prescription for an engine dilema
 

I think you have answered your own question here quite nicely. The engine is in the Guardian mode so power is down substaintially and the crankshaft and camshaft codes indicate that something is wrong and its not clearing itself. You need to scan the fault history and see what events if any may have led to this fault mode. Then the rest of the ideas you list are an excellent way to pinpoint a problem that may be as simple as some loose or slightly corroded conections in a sensor to something more serious in the engine. I am not sure I understand one blue input that says to much oil, does this mean you added to much oil or that the dipstick all of a sudden shows an increase in oil level. If it does you could have added a lot of water to the oil with a problem and since water is heavier than oil it will sit in the bottom of the oil pan and also raise oil level if it is a substaintial amount of water,. Has the coolant level gone down at all? In any event you've got a problem here and you sould like you have the skill set and ability to track it down. Best of luck finding your issue, hope its minor.

Best Regards,
Ray @ Raylar

Great and hanks...to clarify I have not validated I am in Guardian Mode yet...I might need to do a engine scan to get that...guess it should not been in blue. But I will begin troubleshooting with my above list....

I just wanted to validate that I did not miss anything...this list is an example of all possibilities.