Merc optimax 150 (2002) rough idle (with video)

[phyrefighterjay]

just typed the best description of what my engine was doing....hit send and lost it allllllll
all of the simple stuff has been tracked down....filters are new, plugs are good...the only thing that the videos dont show you are when its on plane. it cuts out when its on plane about 200 rpms and my fuel consumption goes from 5.5 gph to 7 gph at 3500 rpms....then it will sometimes snap back into regular running mode (5.5)
what we know....
fuel is good, no water
filters plugs and wires are good and plugs are gapped
elec connections are good and tight.
Batts are good (i load tested them
as you look at these videos of it running at low idle, remember it sometimes cuts out 200rpm while its on plane as well. I am trying to sell the boat/motor combo. So i need help getting it back to a normal running state. The third video shows it running with the plastic Flywheel cover off… Maybe the belt tensioner is too loose and needs to be replaced? Thank you for your help

[JOE54]

check for spark when on all 6 when problem occurs

[EuropeanAM]

Also check the Air Compressor for lateral movement, etc.

Belt should be replaced at LEAST once every 3yrs/300 hours (whichever occurs first). The 2.5L belt tends to stretch, and will allow the tensioner bracket to contact the alternator/bracket (once that happens, severe wear and performance problems are likely).

I agree with Joe... spark and spark plugs (don't forget to inspect wires) are a GREAT starting point.

[phyrefighterjay]

It was a bad coil

[JOE54]