I need help 5.7 Mercruiser EFI

[sea ray 245]

Hello everyone , Here is my problem I have a 2001 Sea Ray with a 5.7 EFI mercruiser. Boat starts, idles perfect around 750 , tops out great , around 4300 rpm's nice and smooth. But when I bring up to and only to 1000 rpm's run's rough to the point it will shake the boat. If I nudge up to say 1200 and further it nice and smooth again. Or if I go below the 1000 rpm to 900 and under it' smooth again. This will do this in gear or sitting at the dock in neautral . I have just replaced the wires ,plugs, dist cap and rotor, and a new coil but still the same problem. Could this be a sensor going like map , IAC, throttle positioner , I have no more IDEAS. Went today and made an appointment at our marina to have it put on there computer so I hope it show's something. Does anyone have any ideas what could be causing this? or maybe has had or seen this same problem somewhere else. Otherwise the boat runs great . Thank you

 

[Dshow]

Re: I need help 5.7 Mercruiser EFI

First thought is the 4300 RPMs sounds a little low, it should be 4400-4800 RPMs. Is the engine actually running rough around 1000 rpms or it is possibly a mechanical harmonic at that speed that makes the boat shake?

 

[sea ray 245]

Re: I need help 5.7 Mercruiser EFI

Thanks I thought the 4300 seem low but I was not sure. What is the Harmonic balancer and How is this fixed.

 

[NHGuy]

Re: I need help 5.7 Mercruiser EFI

No he didn't write balancer, he wrote harmonic. Harmonic refers in this case to the vibration being due to the balance of the engine components at your annoyance RPM of 1000. You should hope though that the diagnostic they do at your dealer turns up a bad component. That's cheaper than engine work.