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Twin Merc 7.4 MPI Electrical Issue?

One engine is the problem, the other engine is following ecm commands.... The engines are possibly linked together so when one engine goes down RPM are reduced on both... Which MPI do you have? L29 or the Lingenfelter set up?​
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How would I determine which MPI I have?
 
The fact that the ECM`s may be communicating with each other is a sign there joined together and needs to be addressed first
 
If the voltage drops when the engines die off it may be from combined electrical system , 1 dead alt, and the other alt getting ready to die. If they were truly independent only 1 motor would be affected not both.
Like I said earlier test the system to find out beacuse it looks like the same boat I worked on a few years ago and it had the wires combined and drove me nuts
If you still got my cell, give me a ring
 
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Bt Doctur said:
If the voltage drops when the engines die off it may be from combined electrical system , 1 dead alt, and the other alt getting ready to die. If they were truly independent only 1 motor would be affected not both.
Like I said earlier test the system to find out beacuse it looks like the same boat I worked on a few years ago and it had the wires combined and drove me nuts
If you still got my cell, give me a ring
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Was the boat that drove you nuts in Forked River?
 
No PP, any chance you have the Silent Thunder exaust box on the transom?
Aside from the motors blowing the 90A fuse on the starter to losing ign power but still able to crank,finding jumpers on the main buss bar under the dash. Lots of hours to get it back to true dual systems. Next was an exaust reversion issue rusting the valves in the heads on both motors .
Found a fix for that problem , but developed a fix for it. The bad part is once we got it perfect he sold it to go fast person.Moved the battery switches to under the rear seat for hatch motor power access,
and ran a dedicated hatch motor power lead there also .
 
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I don't thing it's the same boat. I bought this from a retired cop (Bob) in Forked River. He had it one year and the wife hated it. They were used to more of a cruiser type boat. He said it came from the Lake of the Ozarks.
 
need a better pic but most likely a filter , should not affect the alt output.
Now if it was added because of a alt whine thru the radios or stereo then the alt has a bad diode
 
Here is the update. I had the port side alternator benched tested and it was down 10amps from what it should have been. Replaced that alternator and finally got to sea trial the boat today and it ran like a champ. Thanks all for the help.
 
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