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Not able to locate source of misfire

M

Medichawk00

New member
Mercruiser 2013 GM 5.0L MPI ECT Alpha1 Gen2 Last season ran fine and maybe once a month start on muffs during winter with out any problems (Live in Florida) took boat out on the water My vessel view mobile is reporting engine misfire and would not go over 10mph and i think 3200rpm was my max wot no OBD alarms. Motor has almost 300 hours this is what i have done so far some i did anyway due to hours and age. I replaced the fuel pump and regulator that is in the cool fuel, ignition coil, cap and rotor, spark plugs, and fuel filter that did solve the surges at idle, fuel pressure is now stable and where it should be which did not solve my misfire. Fuel about 3/4 tank of new fuel did not see any water in the tank or in what i syphoned and let sit in jar. I pulled the spark plugs and they are all still clean and the boat starts instantly even after sitting. You can feel it running rough. Today i still have the misfire and now O2 sensor failure reported in vessel view. The last time one of my O2 sensor failed it did not cause a misfire so i don't think they are related. I did not replace the spark plug wires they appear in good condition before i throw more money at this thing what else should i check what else can cause a misfire any help would be appreciated thank you.
 
Start with the simple things first....
1) verify distributor wired to correct spark plugs by physically tracing each wire. Note that the caps cylinder #'s are often marked for both RH and LH Rotation engines...
2) run a compression check on all cylinders.... warm engine, no plugs in, throttle wide open.
3) how old are spark plug wires? Sometimes get fritzy while still "lookin good"
 
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I traced each wire twice and checked the cap the second time, I am pretty sure the wires are original. I will do the compression test Monday. Thank you
 
This is an emission controlled engine..... Mercruiser may have an ECM reflash for this.... The reflash ignores low RPM misfires....

Things to look at, Make sure you do not have the Yellow Flag circuit breaker.... This will cause the ECM to rack up misfires.

Make sure the balancer is not loose.

This is the service bulletin number for EC Engine Misfires...Bulletin No. 2011-11R2 OEM No. 2011-07R2

"Diagnostic Information
This bulletin provides information on the probable causes of the "Cylinder Misfire Limit Exceeded" fault and outlines a
diagnostic procedure to efficiently resolve the fault. Cylinder misfire in 4‑stroke gasoline engines can be caused by many
different engine systems and components. Cylinder misfire is not something new and unique to MerCruiser ECT engines. What
is new is the PCM’s ability to detect cylinder misfire and set a diagnostic fault."
 
I do have the yellow flag one, I also ran it again today[FONT=&quot] and had white smoke or steam coming from one side of the exhaust and the riser on that side was alot hotter than the other pulled plugs and one had a little bit of what i think oil on it. Thanks[/FONT]
 
I ran it today on muffs had white smoke or steam coming from one side of the exhaust and that riser was a lot hotter than the other side. I do have the yellow flag one and will look into reflash and I will check the balancer. Thank you
 
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