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2004 Mercruiser 50 MPI

C

cdgogan

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"I've recently purchased a

"I've recently purchased a used 2004 Regal BR with a Mercruiser 5.0 MPI engine. The boat works beautifully coming out of the hole and cruises along nicely between 30 - 40mph. When I attempt to "open it up" as soon as the RPMs get to 4600 the engine begins to fluctuate. The TAC does not identify any fluctuation in RPM but the engine sounds as though it is "missing". I've played with the trim to see if that might be the issue but regardless of trim setting, the fluctuation is present.. Consistant at @ 4600 rpm. Any thoughts?"
 
"From what I've read onlin

"From what I've read online, it shouldn't be kicking in until atleast 5000 rpm. There is the possibility that the TAC is not reading accurately but the resulting fluctuation doesn't seem right. Does anyone know what the result (sounds / feeling) is when the Rev Limiter engages? I wouldn't think it is as ugly sounding as what I'm hearing."
 
Sounds/feels like a plug is no

Sounds/feels like a plug is not firing or it's running on 6 cylinders instead of 8. The computer is interrupting the firing order by pulling spark. If all is well up till max rpm that's probably what's happening. Put a shop tach on it to confirm tach reading.
 
I believe the MEFI ECU and the

I believe the MEFI ECU and the ECM555 actually limit fuel flow rather than shutting down spark. There was a warning on "offshoreonly.com" about running near or on the rev limiter as you get a very lean mixture and can destroy pistons etc.
 
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