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Mefi1 guys please HELP! 502 efi GenV problems with Mefi1

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Old 07-31-2022, 08:24 AM
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Originally Posted by AP700
key on 423 is 0.04v
key on 423 is 0.00v
on j2 connector without ecm hooked upstarting the engine isnt possible right now because i have disassembled the intake manofold to check the harness.

i have 2 modules, thought maybe the 1st was bad. both are merc
Originally Posted by AP700
did try everything. don't know what to do now with this. anyone?
Did you get the intake back ON, and if so what are the voltages with motor running
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Old 08-15-2022, 02:34 AM
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Okay something interesting happened to me. What I tried was, Igniton off, apply DVOM to 423, IGNITION ON. Measure ckt 423 to ground, should be over 3000 Ohms. apply + to ckt 424, Ohms on 423 should change to under 1000. It did the reverse thing. Ohms were unter 1000 and when i applied + to 424 it changes ohms on 423 to over 3000.

I have seen the manual says IGNITION ON in chapter "7.4mpi/8.2MPI MEFI1".
Inchapter "7.4MPI Mefi1" it says IGNITION OFF.

With the Ignition OFF, everything is okay, I have over 3000 Ohme in CKT 423 and under 1000 Ohms when i apply + on CKT 424.

Maybe i just had the wrong chapter in the manual? My Engine is a 502 EFI GenV F419717






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Old 08-15-2022, 04:15 PM
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You should be using manual 16 for VST and MEFI 1
Manual 23 is for cool fuel and MEFI 3
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Old 08-16-2022, 12:14 AM
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Okay i just looked in the Manual 16. It says ignition ON. so my ignition does not work as it should.

Don't know what to do now.
3rd Ignition control module
2nd Ignition coil
2nd pick up coil
Harness has no opens or shorts

Why does my ignition module have under 1000 Ohms and changes to over 3000 ohms when i apply 12v+ on ckt 424? should be the opposite way, and it is when i have the ignition OFF.


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Old 08-16-2022, 07:40 AM
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Don't know if there is a misprint in the manual or not (its happened before), I've never checked the ohms readings. That said, being opposite could mean ECM issue
As I understand what you've said prior, is J2-24 is not seeing 4.5V

The ECM is not switching so I'm thinking the ECM issue

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Old 08-17-2022, 12:14 AM
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Yes I just want to double check if its the ECM. I have also a Code 33 everytime i switch ignition on. Map sensor is new, voltages are good, even the real time readings on the ecm are good, and it throws a code everytime. I think the ecm is shot. I try and put together the engine and read the voltages on the ignition system. Maybe its just the ECM.
But mefi1 ECM is hard to get, especially in germany.
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Old 08-17-2022, 05:23 AM
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Originally Posted by AP700
Yes I just want to double check if its the ECM. I have also a Code 33 everytime i switch ignition on. Map sensor is new, voltages are good, even the real time readings on the ecm are good, and it throws a code everytime. I think the ecm is shot. I try and put together the engine and read the voltages on the ignition system. Maybe its just the ECM.
But mefi1 ECM is hard to get, especially in germany.
https://www.boatunlimited.com/
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Old 08-17-2022, 07:00 AM
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Agree, a MEFI 1 is hard to find, and can see the extra issue being in Germany. I have my old one removed from my VST 502 when I repowered to MEFI 3 and cool fuel. OBDiagnostics has a listing for the M1 but don't know if Bob has any, and like John at Boats unlimited can test and maybe repair. A couple guys at iboats has contacted John about test/repair and he's told them he's so busy he doesn't have time right now. He may have freed up some time over the last couple weeks and may be worth contacting
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Old 08-18-2022, 07:17 AM
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Question.
when at 424 is no voltage applied, 423 is grounded.
When at 424 voltage is applied, 423 goes to the transistor.

Why does the manual say i should have less resistance between 423 and ground when 424 is energized? should be the other way around, like it is on my engine. or am I wrong?
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Old 08-18-2022, 07:37 AM
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I don't fully get it either other then they are taking into account what resistance changes happen inside the ECM. I like test which verify the ECM is working correctly, like voltage measurements on the pins during start and run. If this is happening correctly and still getting code, then it has to be ECM
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