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Merc 700sc RPM

Old 10-02-2020, 09:01 AM
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I find it hard to believe that there are presumably several boats with this condition at the same time. Is this a year 2000 clock issue??? lol

I never had this problem on my 700's, sorry can't help - but interested in what you guys found out. I've got a diagnostic manual if you need any screen shots from that.
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Old 10-02-2020, 03:06 PM
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This is from BUP John Mosetti: The 600 and 700 and so do the OPTIMAX engines suffer failures within the PCM 555 for the coil drivers when a bad ignition coil(s) happens. You can check for faults in with the scan tool to see if any of the coils have failed and or the internal ignition coil drivers in the PCM 555. At times this fault will not show either and or is logged in history
John can test the PCM555 and update the internals. He explained it as we are running very old tech, like an old computer, cell phone, TV, that needs to be current to run efficient, faster and stronger.
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Old 10-02-2020, 04:16 PM
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I would be interested in getting my PCM tested and updated. My Rinda scanner doesn't show a fault. How would I contact John?

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Old 10-03-2020, 01:09 AM
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Originally Posted by bcevans8
Both motors run very smooth and idle at the exact same speed. Both motors will only rev to 4,000. While it is possible that it is a bad coil (coil packs are original), what are the chances that both motors experienced a coil failure at the exact same time?

At 4,000 the motors sound and run great. There is no mis-fire or hesitation.

Thanks.
In the thread you started in the General Q&A section, you mentioned that it ran great before removing the anti-siphon valve, replacing fuel/water separators and replacing all the spark plugs. If you gapped the plugs too wide, the spark will find another place to go when cylinder press reaches a certain level.

Last edited by zz28zz; 10-03-2020 at 01:11 AM.
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Old 06-15-2021, 02:02 PM
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The issue was the high pressure fuel filters. They were clogged and did not allow sufficient fuel flow at high RPM and full load.
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Old 06-15-2021, 02:09 PM
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Originally Posted by bcevans8
The issue was the high pressure fuel filters. They were clogged and did not allow sufficient fuel flow at high RPM and full load.
Yep, the little ones mounted up on the engine...
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Old 11-15-2021, 07:25 PM
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Good evening.

The solution to my RPM issue was the high pressure fuel filters at the back of the engine. They were clogged to the point that they would not flow enough fuel at higher RPM. We replaced them and it runs like a champ.
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