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Dominick, Marine Mechanic
Category: Boat
Satisfied Customers: 1009
Experience:  25 Years Experience as Mechanic, 20 Yrs Boat Yard Owner/Mechanic, Factory Certified
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I have a 2010 mercury 225 optimax. I had poor compression in

Customer Question

I have a 2010 mercury 225 optimax. I had poor compression in all cylinders and had a new long block put. in. Now I have the same problem as before it was rebuilt at around 4600 rpm I loose power you can hear it in motor it is almost like rev limiter is kicking in. I can hole rpms at 4600 to 4900 but can not get beyond that. I have checked air and fuel pressure at the higher rpms and is good also compression is fine.
Submitted: 2 years ago.
Category: Boat
Expert:  Joe replied 2 years ago.
Thank you for allowing me to assist you, my name is ***** ***** I will be happy to assist you with your concern today.
Have you tried running the motor from an external portable fuel tank thus to eliminate potential problems with existing fuel system?
Have you checked for contaminants in the fuel?
Have you checked for misfires in spark?
How does it run otherwise (below 4600 rpms)?
Customer: replied 2 years ago.
runs strong below 4600. drained and put all new 91 octane fuel added new in line water separator and filter. Have 92 psi fuel pressure at all rpms. How would you check for misfires in spark. Is that related to stater ?
Expert:  Joe replied 2 years ago.
And you have found nothing in the separator, correct?
In terms of misfires in this setting I would use a timing light and check that each cylinder is firing correctly.
What is the voltage at the battery with engine running?
Customer: replied 2 years ago.
We put in a new starting battery because ecu was indicating low voltage good now.
Customer: replied 2 years ago.
I would assume that since the engine is running smooth at idle and lower rpms that cylinders are firing correctly.
Expert:  Joe replied 2 years ago.
A new battery could provide a better reading but I would still need to know exactly what the voltage is reading with engine running.
In terms of cylinders firing this is actually not fully correct, there can be problems at higher rpm's only and thus why it needs to actually be checked because if things are assumed things can accidentally get overlooked thinking they are ok.
Has it been scanned for codes yet as well?
Customer: replied 2 years ago.
we scanned it right after rebuild to set hours to zero and also so it would add extra oil through break in period there were older fault codes. I am thinking I should have it scanned again after break in and running it a higher rpms to see if it throws any codes. Will the ecu retain all codes in this model of motor.
Customer: replied 2 years ago.
we cleared old codes at the time we rezeroed hours.
Expert:  Joe replied 2 years ago.
Certain codes it will retain in history, others will not.