Merc 225 OB mystery problem

[TCS]

I have a 1997 Merc 225 offshore counter-rotating engine that will, at its own discretion drop 1000-1500 rpm's and then surge back. mechanic has tested fuel pump and all obvious causes. fuel pick-up & fuel system seems Ok I believe problem may be electrical-when engine drops RPM guages act weird momentarily. We have been pursuing this mystery for months now. other matching engine is fine, prblem is intermittant but getting more frequent, it never happens when mechanic is aboard with test equipment, when problem is not present engine runs perfectly<br />HELP PLEASE!!!

 

[MERCMAN]

Re: Merc 225 OB mystery problem

Check the main engine harness where plugs into engine these are bad about not making good connection unplug and slightly spread pins and i bet your problem goes away hopefully.

 

[Fitch]

Re: Merc 225 OB mystery problem

When the tack drops it is usually a sign of a rectifier problem. I think they had that problem that year. Might becausing a heavy load on charging system cauing loose in rpm.

 

[bassingrs]

Re: Merc 225 OB mystery problem

TWO YEARS AGO MY 200EFI MERC. DID THE SAME THING.I WAS USEING NGK PLUGS AT THAT TIME.I PURCHASED TWO NEW SETS IN ONE SEASON.I WAS ON THE ROAD FISHING WHEN THE PROBLEM BEGAN TO BE MORE FREQUENT.I STOPPED AT AN AUTOMOTIVE STORE TO PURCHASE ANOTHER SET OF NGK PLUGS. THE STORE DID NOT HAVE THEM SO I TOOK A SET OF A/C EQUIVELANT.THE PROBLEM STOPPED,AND HAS NEVER RETURNED.ANOTHER BENEFIT,THE PLUGS WHERE VERY CHEAP COMPARED TO NGK.TRY THIS IT WAS A VERY CHEAP EXPENSE IF IT DOENT WORK YOU WONT BE OUT MUCH. BASSINGRS

 

[Big Rod]

Re: Merc 225 OB mystery problem

"Ditto" on Bassrings post, NGK's are not bullet proof, happened to me too...

 

[HHI3]

Re: Merc 225 OB mystery problem

Some gas lines are multiple layers and the vacuum created by the fuel pump pulling gas out of the tank can seperate and collapse the inner layer of your line.....causing the exact symptoms you are talking about. Mayby you could switch your lines and see if the other moter does it.