2006 Merc 40HP 4 Stroke EFI runs rough and low rpm at WOT

FairbankFrank

Recruit
Joined
Jul 10, 2011
Messages
2
I have a 40 HP Merc EFI 4 stroke bigfoot. the motor starts easily but idles rough and continues to idle rough. It almost sounds like one of the cylinders is not firing. how can I check spark without doing any damage? RPM at WOT is 4200, manual says it should be 5500 -6000
 

BBDAWG

Seaman Apprentice
Joined
Jul 9, 2010
Messages
41
Re: 2006 Merc 40HP 4 Stroke EFI runs rough and low rpm at WOT

I have the same problem on same engine. I can however get a little more rpm, up to 4950. At 2500+ engine sounds great but under 2500 it "sounds" like a cylinder is dropping out.
 

Jeep Man

Commander
Joined
Oct 17, 2008
Messages
2,803
Re: 2006 Merc 40HP 4 Stroke EFI runs rough and low rpm at WOT

I would suggest cleaning the injectors.
 

FairbankFrank

Recruit
Joined
Jul 10, 2011
Messages
2
Re: 2006 Merc 40HP 4 Stroke EFI runs rough and low rpm at WOT

I did find out the problem here. the Number 4 coil was pooched. Replaced the coil the engine runs like new now.
 
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