Mercruiser5.0 ltr ECM Problems

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Rob Skrzypkowski

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I wondered if any one can help me. I have a Mercuiser 5ltr EFI, year 2000, Serial number L694472. Basically the engine will not start. I have found that I have 12V to the + side of the ignition coil but - side is open circuit. I have traced this white wire to the ECM (I think the ECM is a MEFI-3). I cannot get a closed circuit from the ECM in either the off or run position on the ignition key switch. The question I would like to ask is could I simply install a - wire to the coil. I really don't fancy paying $700 for a new ECM also I don't want to damage any other parts by doing this.
 
Don S

Don S

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Re: Mercruiser5.0 ltr ECM Problems

The white wire from the coil is not a ground, so no you can't just make a new ground for it.
How exactly did you test the - side of the coil for voltage? Where exactly did you have the test leads of your meter for the test.
I assume you are not following any kind of a manual, is that correct?

PS The chances of the ECM being the problem is low.

Are you getting spark from the coil while cranking?
 
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Rob Skrzypkowski

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Re: Mercruiser5.0 ltr ECM Problems

Hi Don,
Thank you for getting back to me, I did wonder about the "white wire". I simply tested for continuity from the - side of the coil to the - side of the battery with a multimeter. You are correct as I am not following any kind of manual.
 
Don S

Don S

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Re: Mercruiser5.0 ltr ECM Problems

Are you getting spark from the coil while cranking?
 
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Rob Skrzypkowski

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Re: Mercruiser5.0 ltr ECM Problems

Hi Don,
I have no spark, this is what prompted me to check the supply to the coil.
 
Don S

Don S

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Re: Mercruiser5.0 ltr ECM Problems

With power off, check the primary and secondary resistances of the coil.

Ohms test on coil.jpg
 
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Rob Skrzypkowski

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Re: Mercruiser5.0 ltr ECM Problems

With the power of and the - wire removed. On the primary when the meter is set to 200 ohms the meter reads 0.9 and on the secondary when the meter is set to 20K ohms the meter reads 7.82.
 
Don S

Don S

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Re: Mercruiser5.0 ltr ECM Problems

Here is some troubleshooting info for your system.
I edited out all the info for the other type ignition used so it doesn't confuse things.

View attachment TBI TB MEFI3.pdf
 
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