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2012 Mercruiser 377 Mag 130hrs A slight missing mostly

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2012 Mercruiser 377 Mag 130hrs A...
2012 Mercruiser 377 Mag 130hrs
A slight missing mostly noticeable when throttling up. (on trailer). Did a complete tune up late last year and all was great. Got the boat out for this season and noticed issue.
Used my Techmate Pro:
No Codes, Guardian not activated
In Misfire screen as the engine is running, shows #8 cylinder is misfiring at idle every cycle, going up about 1 a second. Increasing rpm past 1500 and the misfiring stops for #8 and starts for #2 cylinder. Go back to idle and #2 misfiring stops and #8 starts going up again.
I changed plugs, wires for these two cylinders. Checked rotor cap and used inline spark tester and all appears good. All these still appear like new....only put about 3 hours on new parts last year.
Next I check compression and both cylinders are just over 180.
Next I swapped fuel injectors from cylinders that do not have an issue and still have the same issue with these two cylinders....problem did not follow the injectors.
Submitted: 3 months ago.Category: Boat
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Customer reply replied 3 months ago
This is a Catalyst engine also.
Answered in 1 day by:
3/20/2018
Marine Mechanic: Boat Doc, Boat Enthusiast replied 3 months ago
Boat Doc
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