I have twin 2006 496HO's and just had plugs changed as normal maintenance at a service shop a couple of weeks ago. Boat ran great all weekend until the end when I noticed the port motor is likely running on 7 because when under load it was 300-400 rpm down. At idle it sounds normal or close to normal-, hard to tell.

How do I find out in my driveway or on the hose which cylinder is not firing? It may be just a loose plug wire or cracked plug that needs to be replaced. If I check all the wires I am not sure I can tell the difference in idle as the computer kinda fixes itself.

I don't have a Merc. scanner or a Rinda tool to check cylinders, was thinking about using my thermometer gun to point at manfolf to see which area is hot and which cylinder is not. As you can tell I am not a mechanic but would appreciate if anyone knows any quick trick to isolating the cylinder. Any advise would beat a long haul to the water or added expense at a shop.

Thanks in advance!

it may just be a wire but....at idle it may very well be on all 8. Mine sounded fine idling. pulled them to add some headers and Precision found a bad coil pack... I was loosing hp/rpm as well on that motor.

How do you tell if a coil pack is bad? Or is this a mechanic only deal

grab each wire until you dont get shocked

now that's funny AND it'll work

not sure how they figured it out.

Ask around on who's got a rinda scanner close to you. you can check ignitions, injectors,& perform an induced misfire test one cylinder at a time. I had same issue turned out just a plug change.

Fastest way with no scanner is pull plugs abd see if one is wet.

Wannabe

inline spark testers while the motor is running or a spark tester - we use stevens. Anytime checking for spark make sure doing so in a very well vented engine compartment along with no gas leaks. Run the blower also helps

Also a proper scan tool or Rinda / diacom.

next swap coil paks from cyc. to cyc along with spark plugs to C if problems follows or stays the same.