4.3LX to 4.3MPI wiring conversion

brs335249

Cadet
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Jul 9, 2011
Messages
8
Greetings,
I am finishing up changing out my old 4.3LX(Mr. frosty got her) to a newer 4.3MPI. The main 10 pin connection seems to be the same but I was wondering if I might have to change anything. I did download the manual for $17 and that wiring harness looks harder than Chinese math! Anyone ever do this swap?

Ben
 

TilliamWe

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Dec 21, 2004
Messages
6,579
Re: 4.3LX to 4.3MPI wiring conversion

If you got a COMPLETE 4.3MPI Mercruiser, it should be a "plug and play" swap. Everything is contained on the motor, so plug in the plug, hook up the starter wires, and a ground wire and you should be just about ready.
 

brs335249

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Joined
Jul 9, 2011
Messages
8
Re: 4.3LX to 4.3MPI wiring conversion

The motor was complete but I believe it sank. I went through it mechanically and it has hardly no hrs on it. I dusted the cyl walls and put new rings in and I'm hoping the electronics are not damaged.
 

brs335249

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Joined
Jul 9, 2011
Messages
8
Re: 4.3LX to 4.3MPI wiring conversion

Update...motor is hooked up, I have fuel pressure and the motor will turn over but it does not start. HELP...what is my next step?
 

Tail_Gunner

Admiral
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Jan 13, 2006
Messages
6,237
Re: 4.3LX to 4.3MPI wiring conversion

Update...motor is hooked up, I have fuel pressure and the motor will turn over but it does not start. HELP...what is my next step?

If the motor that sank was the FI motor and the ecm was under water it is almost assured its Under Water.. Take the boat to a merc dealer and see if there diag comp can talk to the engine...i really do not believe a ecm could survive something like that...I hate to say this but it takes a great deal of working knowledge to convert a motor in such a fashion...What type of igntion did the old motor have....Is your boats wiring harness pinned correctly to the new efi system...I truly suspect it will be cheaper to pull the FI off the new engine and go to a carbed motor...
 

brs335249

Cadet
Joined
Jul 9, 2011
Messages
8
Re: 4.3LX to 4.3MPI wiring conversion

If the motor that sank was the FI motor and the ecm was under water it is almost assured its Under Water.. Take the boat to a merc dealer and see if there diag comp can talk to the engine...i really do not believe a ecm could survive something like that...I hate to say this but it takes a great deal of working knowledge to convert a motor in such a fashion...What type of igntion did the old motor have....Is your boats wiring harness pinned correctly to the new efi system...I truly suspect it will be cheaper to pull the FI off the new engine and go to a carbed motor...
I'm thinking that I need to jump out the two outside wires on the shifter connector but not sure about the two gear plug???

There is no code reader available for this motor. like a flashing LED light? I hate to spend $400 if the ECU is bad
 

dubs283

Vice Admiral
Joined
Jul 27, 2005
Messages
5,058
Re: 4.3LX to 4.3MPI wiring conversion

I'm thinking that I need to jump out the two outside wires on the shifter connector but not sure about the two gear plug???

There is no code reader available for this motor. like a flashing LED light? I hate to spend $400 if the ECU is bad

if you have no spark there could be any number of issues with the igniton system ranging from a bad crank sensor to faulty ECM

the first step to connect a scan tool to see if it communicates with the ECM, then you can start to troubleshoot and rule out possible issues
 
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