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2016 90hp mercury Missfire

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Bozo

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Wondering if anyone has had a problem with this motor having an intermittent misfire develop after cruising (25knts) for approx. 1/2 hr or longer. When I stop the engine and restart the misfire goes away. I have replaced the coil packs, leads and plugs so it is not any of those items breaking down. The engine drops about 200-300rpm. It does not play up every trip. The mechanic could not find any fault codes, and when it plays up the vessel view system says everything is OK.
 
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Bozo said:
Wondering if anyone has had a problem with this motor having an intermittent misfire develop after cruising (25knts) for approx. 1/2 hr or longer. When I stop the engine and restart the misfire goes away. I have replaced the coil packs, leads and plugs so it is not any of those items breaking down. The engine drops about 200-300rpm. It does not play up every trip. The mechanic could not find any fault codes, and when it plays up the vessel view system says everything is OK.
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I have 2010 115 hp 4 stroke Mercury Outdrive and my issue sounds similar to yours. My engine went into a preservation mode that would let me run under 3k rpms when the faults happened, restart and it usually cleared up. My intermittent became more frequent and several mechanics could not id issue, lots of coil packs, plugs, injector clean. no codes at first then codes started showing up but they were a bit random, we changes some sensors based on codes no change. It came down to "WIRE WIGGLING" and we found a "short" in primary engine wire harness that was causing the five volt system that runs sensors to drop off sending chaos into the sensor codes and thus engine would go into protect mode. Good Luck
 
Thanks jpburnard,
It could be a random wiring problem, who knows at this stage. It has always played up after i have been cruising for a while and the misfire won't stop until i stop and restart the engine (only discovered this last trip). Last fishing trip It took me two hours to get to the reef at about 18knts max speed and i had no problems. Only when the weather is good and i can cruise fast for a good while does it play up. Some suggest it could be the Hp or Lp fuel pumps, but i don't want to go and just replace them at $820 plus fitting for the whole unit.

If i could explain the misfire a bit:- When it is misfiring it isn't constant, like running on one less cylinder. They engine is running good then for a second the engine will misfire and then be fine. Travel for a few more seconds or more and it will do the same. Doesn't matter what rev range i am in or load on the motor. It will act the same.
 
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Well I think the problem is resolved. I spoke to the local dealer, and he almost guaranteed that the "Shift Sensor is faulty. When it plays up the shift sensor thinks the engine is in neutral and revving to high, so it tries to cut the revs down (misfire). Does not always log a fault code he said. Turning the engine off resets the sensor.
 
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