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Searay / 350 MAG Engine Misfire Error

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Chris Martin

New member
I have a 2008 Searay 250SLX with a mercruiser 350 MAG. Since the middle of last summer I have been getting a System Fault (Engine Misfire) (STBD System Fault 71). I have taken it to the only local Mercury shop and they have been unable to resolve the issue. When they connect their computer, the data does not provide and specific information. They have changed it distributor cap, plugs, etc, but no resolution. Has anyone run across this scenario before?

Engine Serial - 1A304222
 
I am not experienced with the EFI models so this is only a guess based on the manuals I have.

If your system uses PCM 555 and you are seeing a code 71

this is what I found.
If this is not relevant to your efi system then disregard.

There are a few here who do have efi experience though so maybe they will chime in and confirm or deny my info.
 
Chris Martin said:
I have a 2008 Searay 250SLX with a mercruiser 350 MAG. Since the middle of last summer I have been getting a System Fault (Engine Misfire) (STBD System Fault 71). I have taken it to the only local Mercury shop and they have been unable to resolve the issue. When they connect their computer, the data does not provide and specific information. They have changed it distributor cap, plugs, etc, but no resolution. Has anyone run across this scenario before?

Engine Serial - 1A304222
Click to expand...

Hello Chris,
I have what sounds like the exact same problem that you had, below are my details. Did you find a fix? If so would you please the details? Also if anyone else has had or heard of this same problem please, let me hear from you. Thank you in advance to everyone.

2012 Cypress Cay Cayman 250SLE Pontoon Boat
powered by a Mrecruiser 350 MAG MPI with a Bravo 3 outdrive, PCM 555, I bought the boat new and now it has approximately 450 hours.
Engine Serial Number 1A655948,
Drive Serial Number 2A002728


Starting last Fall 2019, while running at 3/4 throttle to near WOT my SmartCraft gauge would most of the time, go into Guardian Mode, limiting engine power and sounding several audible alarms. The SmartCraft gauge details of this alarm are;


“OBD Service Soon”
STBD system fault 71 engine misfire detected.


...last Fall after some research I installed four new O2 sensors, re-gapped and installed 8 new spark plugs and all new spark plug wires, a distributor cap and rotor. Then after a pretty aggressive test drive it seemed my problem was fixed. The work and test drive were done at the end of fall going into winter so I was happy with my results for the season.


Fast forward to today, April 4, 2020, it’s a beautiful day, temps in the low 80’s without a cloud in the sky. I head down to my boathouse, start my boat and back out and cruise around for a couple of hours with no problems. I had been driving at many different speeds but no more than 3/4 throttle. It’s now time to head back to the house so I take off and throttle up to about 1/2 throttle for a few minutes then 3/4 throttle for a couple of minutes and then go to WOT for about 3 minutes. I’m running about 45MPH at 5100RPM’s, my SmartCraft Gauge sounds several audible alarms, the engine goes into Guardian Mode limiting my engine power. I immediately throttled down to neutral and floated to a stop. Throttling down stops the audible alarms but the engine remains in Guardian Mode for about 45 more seconds or so, then I proceed home about 1/3 to 1/2 throttle with no issues.
David
 
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