motor revs

[simply]

Have just purchased a 50hp 4 stroke motor on my boat. The motor at varying times will drop revs by about 4-600 rpm. This will last for1-5 secs and then will pick up again. The dealer can't find whats causing it but was happy to charge me Au$1000 for the info. The computer printout shows no fault codes. My basic mechanics suggests to me it is therefore the ECM. As this is an expensive replacement on spec, any ideas? Please? Thanks in advance.

[JUST-IN-TIME]

run off a brand new tank and fuel line
pump primer bulb if motor picks up bad fuel pump

[simply]

Thanks. Have run 5 tanks of fuel thru. All fuel mods done. Still hasn't solved the problem. Played up again yesterday.??????

[simply]

Took the boat out on the weekend and the motor played up again. This time, the alarm sounded as well as dropping/ missing the revs.
This does not sound like a fuel problem. Anyone?

[simply]

Had the complete fuel system serviced on the boat and motor. Used it on the weekend and the fault/miss is still there!!!! The alarm came on twice when the motor didn't pick back up again. It sounded as if was running on two of the four cylinders. No fault codes were registered on the ECM Anyone?!? PLEASE?????

[simply]

No offers? Not surprising, two Merc dealers and $2000 can't find the fault either!!! Matbe I should get a grey motor next time. Bye.

[boats.net]

Have cooling system check to see if overheating, have oil pressure tested.

[simply]

Yep. All tested by last mechanic. No problems showing. What are the causes for the alarm to sound? Different alarm tones for different faults. Had two different so far.

[JUST-IN-TIME]

alarms is either over heat or low oil pressure
if this is fuel injected it could be a faulty sensor
they did have problems with the fuse links for charging system

[MACH 5]

Check all grounding connections thoroughly .

[simply]

Thanks guys.
Took the mechanic out last Thursday so he could experience the fault but of course, with an intermittent fault, it didn't miss a beat. I think I have him convinced now its not a fuel problem but an electrical one where one or more cylinders miss fire.
Used it for the 4 days after on a fishing trip and yep, played up every day

Yes its a efi motor so will have them checked.

Thanks for your help