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ECU error code 81?

Old 05-27-2024, 09:21 AM
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Default ECU error code 81?

I have 502 Mag MPIs (OLO85798) one engine had the mefi 3 replaced with mefi 4 by the previous owner, and that engine is throwing code 81.
The engine runs fine, makes full power, just started throwing that code (triggering the audible alarm) on start up yesterday.

Since Mercruiser never used mefi 4 from the factory, Iím not finding a lot out there but other GM based marine engines used mefi 4.
At planetnautique there is a user manual for mefi 4 and on page 153 (337 pages total) says it could be an injector problem. Also, I canít clear the code using the ďnon scanĒ method of advancing the throttle to 100% and back to zero while ignition is on, the engine off, with the paper clip inserted into the diagnostic port as previously described on this site for error code reading.

Any ideas? I plan on buying the rinda scanner, but that will take a while to get here. Is it possible to run the engine despite the code being thrown? It seems to run as well as ever.
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Old 05-27-2024, 07:10 PM
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may want to ohm out the injectors,,look for 1 that may have been changed,,could be a wrong injector.
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Old 05-27-2024, 07:18 PM
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Thanks for the advice. The injectors are the same for the last 800 hours/ 4 years, but maybe one is going bad.
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Old 05-28-2024, 05:36 AM
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Old 05-28-2024, 06:05 AM
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Thank you both.
i don’t think this generation 502s have crank or cam sensors, and given the engine runs fine, I don’t think it’s fuel pump problem. The oil sender on my engines is the 1 wire version, so I don’t think it’s an oil pressure fault (I believe you need the 3 wire for that fault).
I guess I just need to be patient and wait for the rinda scanner. I think an injector fault may be most likely.
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Old 05-28-2024, 06:16 AM
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Artic
are you using mefiburn?
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Old 05-28-2024, 06:23 AM
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Originally Posted by CUOTO
Thank you both.
i don’t think this generation 502s have crank or cam sensors, and given the engine runs fine, I don’t think it’s fuel pump problem. The oil sender on my engines is the 1 wire version, so I don’t think it’s an oil pressure fault (I believe you need the 3 wire for that fault).
I guess I just need to be patient and wait for the rinda scanner. I think an injector fault may be most likely.
I highly doubt your getting a code 81 for a injector itself, it will be in the harness most likely, simply take plenum off, unplug them all and hit them with a ohm meter, will take you 20 minutes. They should show 12-14 ohms give or take. I flow, clean and test these injectors as part of my full time business, other then BROKEN connections on these 502s and low / high flowing injectors, leaking, stuck etc, it is ultra rare to see one with resistance out of range. Since your engine is BATCH fire, other then a open circuit in harness, a dead short in harness or a dead short in a injector, your ecm is NOT sophisticated enough to tell anything else in all actuality. That list of the 16 codes for code 81 is from a mefi4a, smitty

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Old 05-28-2024, 06:24 AM
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Originally Posted by sutphen 30
Artic
are you using mefiburn?
yes
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Old 05-28-2024, 06:28 AM
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Originally Posted by articfriends
I highly doubt your getting a code 81 for a injector itself, it will be in the harness most likely, simply take plenum off, unplug them all and hit them with a ohm meter, will take you 20 minutes. They should show 12-14 ohms give or take. I flow, clean and test these injectors as part of my full time business, other then BROKEN connections on these 502s and low / high flowing injectors, leaking, stuck etc, it is ultra rare to see one with resistance out of range. Since your engine is BATCH fire, other then a open circuit in harness, a dead short in harness or a dead short in a injector, your ecm is NOT sophisticated enough to tell anything else in all actuality. That list of the 16 codes for code 81 is from a mefi4a, smitty
thank you for that, that is good to know. I canít figure out (w/o a scan tool) what else this could be on an engine that seems to run fine.
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Old 05-28-2024, 06:31 AM
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I edited my comment slightly, IF you go back and look at the 16 things for a code 81 on a mefi4a I used for example , you will notice ONLY injector related ones have a check mark in corner so in THAT particular tune, the only thing that WOULD throw a code 81 WOULD be injector related so my initial answer is somewhat INCORRECT but I will still say its most likely in the harness as the ecm cant tell IF a injector itself is not operating correctly mechanically as far as flow and I doubt it would throw that code fr 1 out of the four being unplugged in batch a or b (broken connector)
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