Mercruiser 502 Alarming & Going crazy
06-25-2024 | 09:10 AM
#1
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Joined: Jan 2019
Posts: 26
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From: Greece
Mercruiser 502 Alarming & Going crazy
Hello, and thank you in advance for your help.
I have a Scarab 33 AVS in Greece, with 2x 502mpi. Very well cared and maintained boat, with no expenses saved.
First trial before summer , everything ok.
Next day, when planning at 3K RPM the one engine start alarming with intermittent sound. Only that. When stopped and shut off the engine, iti will not turn on easily. Needed some throttle. Checked oils , temps, psi, everything ok. Checked with Rinda, no faults found. In any way, we (mecchanics) desconected the wiring of the oil reservoir for the lowers.
It stopped alarming for 5minutes of riding, and then started again.We checked again , and we found that the kill switch of the same engine has been faulty. Replaced it , stopped alarming again, for some minutes of "hard ride".
Everything ok, left it docked, next day, when at 3k on plane, engine could not gain RPM. Hardly could achive more than 3.200 while the other one was at 5K. Not alarming (disconected as i said before).
Stopped, Rinda to scan, and....ECM cannot be detected..
And thats where we are now. We changed the harness from engine to cluster (dont know how it is called), but nothing changed in function of the engine or detection for Rinda.
Any idea? anyone with something similar? My mefi3 is dying?
Thank you!
I have a Scarab 33 AVS in Greece, with 2x 502mpi. Very well cared and maintained boat, with no expenses saved.
First trial before summer , everything ok.
Next day, when planning at 3K RPM the one engine start alarming with intermittent sound. Only that. When stopped and shut off the engine, iti will not turn on easily. Needed some throttle. Checked oils , temps, psi, everything ok. Checked with Rinda, no faults found. In any way, we (mecchanics) desconected the wiring of the oil reservoir for the lowers.
It stopped alarming for 5minutes of riding, and then started again.We checked again , and we found that the kill switch of the same engine has been faulty. Replaced it , stopped alarming again, for some minutes of "hard ride".
Everything ok, left it docked, next day, when at 3k on plane, engine could not gain RPM. Hardly could achive more than 3.200 while the other one was at 5K. Not alarming (disconected as i said before).
Stopped, Rinda to scan, and....ECM cannot be detected..
And thats where we are now. We changed the harness from engine to cluster (dont know how it is called), but nothing changed in function of the engine or detection for Rinda.
Any idea? anyone with something similar? My mefi3 is dying?
Thank you!
06-25-2024 | 10:44 AM
#2
Platinum Member
Joined: Feb 2001
Posts: 4,290
Likes: 1,450
From: Virginia Beach
Check wiring harness connections and grounds. That’s the first thing.
I had a similar issue with one of my MEFI-3 502s -it would run well and for a few minutes and then alarm and go into limp mode. Key off and restart and would run fine until 3k rpm. The problem ended up being a knock sensor. The interesting part was that the Rinda wouldn’t catch it unless it was hooked up and monitoring when it happened. Message was, “no knock detected.” The ECM advances timing until it knocks and then backs off - if it cannot detect knock it assumes the knock sensor is bad a faults.
I had a similar issue with one of my MEFI-3 502s -it would run well and for a few minutes and then alarm and go into limp mode. Key off and restart and would run fine until 3k rpm. The problem ended up being a knock sensor. The interesting part was that the Rinda wouldn’t catch it unless it was hooked up and monitoring when it happened. Message was, “no knock detected.” The ECM advances timing until it knocks and then backs off - if it cannot detect knock it assumes the knock sensor is bad a faults.
