I need help with 5.7 EFI Mercruiser

S

SEARAY245

New Member
Oct 19, 2009
18
Boston Harbor
Boat Info
2005 Sea Ray 280 ,Twin 4.3's With Alpha drives. C80 Raymarine with radar
Engines
Twin 4.3's Alpha one gen two drives
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
 
Make sure the spark plug wires are not running close to one of the knock sensors.

The plug wires can induce a signal into the knock sensor wiring and upset the ECM. It will show up only at resonate frequencies.

A known problem.
 
Thanks Chris will take a look . I just installed new wires and had the same problem before . Maybe wires from before were comming close to the knock sensor. love Australia , spent three weeks there last year. Thanks
 
Thanks this does this in neutral also. Could there still be a bad coupler, outdrive input shaft while in neutral . What would be something that maybe imbalanced. Engine runs great at any other rpm just that 1000 starts shacking even in neutral. Would there be a senor that maybe is starting to go bad like IAC ,MAP Im just not sure . it just stinks thats the speed I usually need to dock with and the whole boat starts shacking. Thanks
 
Did the engine ever run smooth at one time and then the roughness started or has it always done this? Answering this question may give me a hint.
 
Sorry was gone for awhile. We bought boat late last fall so we only used a few times before we pulled out of water. I do remember it running rough at the 1,000 rpm mark . I really should of looked into this more than . I told the shop what it was doing , that I was getting vibration around the 1,000 rpm range . So naturally he said sounds like gimble bearing so he replaced , which from me telling him what it was doing I guess that was the right diagnostic. I should of put in neutral and tried and I would of known it was vibrating in neutral to . So to answer your question since we have had the boat it has alway's had this vibration, rough idle at 1,000 rpm . Its like running on 7 cylinders. Once I get past this rpm runs great . Changed filter, plugs , cap ,rotor, and wires. Such a pain to have this vibrate the boat at this speed I use to come to the dock in . the shop is suppose to come down to put on the computer and hope maybe it through a code . Im still waiting. Plugs were changed out and old plugs were gaped at 0.035 new plugs are gaped at 0.045 seemed to run a little smoother with the old plugs being at 0.035 . Maybe im just fishing now. Thanks
 
Last edited:
Change your wires and cap/rotor. At higher RPMs, missing due to arcing or bad wires is not very evident. (I.e. it is hard to hear unless you know what to listen for.). Similar problem with my old Chris Craft. Gave her a tune up and all was well. I had a few bad wires. They looked good, but were not.....
 
Sorry, nevermind. I see your post now about changing cap, rotor and wires. Guess I should read all posts before posting, huh? DOH!!!
 
No problem, Thanks anyway
 
Well had Marina come down and they put on computer ,but they found nothing , everything checked out with the scope. They gave Mercury a call and they think it mabe the engine coupler . Mercury say's to pull boat out of water take of drive and put in the alignment tool and start boat to see how true the coupler is . Does any of this make sense to anyone. I just keep throwing money out there . Don't get me wrong I would'nt mind paying just like to get it fixed right . I just had the drive off last fall and had the gimble bearing replaced . When the alignment was done after the gimble bearing was replaced would they notice or should have none the coupling was going. They also said I should be alright using the boat this way and wait till the end of the season to have done. Will anymore harm be done to the coupler if i keep using.. Just vibrates at 1,00 rpm any other rpm it is very smooth. Thanks
 
SEARAY245 said:
Well had Marina come down and they put on computer ,but they found nothing , everything checked out with the scope. They gave Mercury a call and they think it mabe the engine coupler . Mercury say's to pull boat out of water take of drive and put in the alignment tool and start boat to see how true the coupler is . Does any of this make sense to anyone. I just keep throwing money out there . Don't get me wrong I would'nt mind paying just like to get it fixed right . I just had the drive off last fall and had the gimble bearing replaced . When the alignment was done after the gimble bearing was replaced would they notice or should have none the coupling was going. They also said I should be alright using the boat this way and wait till the end of the season to have done. Will anymore harm be done to the coupler if i keep using.. Just vibrates at 1,00 rpm any other rpm it is very smooth. Thanks
Click to expand...

Get it aligned. It's much cheaper than yarding the engine out to replace the coupler.
 
Hi could this just be out of aligned and the coupler is fine. Or im I looking at replacing the coupler to.
 
I was looking at your problem and it sounds all too familiar. After running at 1000 rpm pull your spark plugs out. You may have water getting into your combustion chamber. I had a similar problem after replacing my exhaust with aftermarket Sierra exhaust and one of the manifolds where defective. If one of the plugs looks brand new its getting wet, and the carbon will be washed off. At higher rpm the cyl would just burn off the water and it would be ok. Good luck!
 
The same thing happens with my 5.0L EFI. It is a PITA when navigating long idle speed stretches. If you find a solution, PLEASE post. I'm going to check my spark plug cleanliness as Moriches suggested.
 
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