Switching to a HEI ignition on 4.3L Mercruiser

Has anyone done this before? My ICM is bad and I don't want to pay $500 for a new one.
I can buy a new HEI aftermarket distributor for $180 with built in coil. Any suggestion?
The motor is a 96 Mercruiser 4.3LX

Re: Switching to a HEI ignition on 4.3L Mercruiser

Yes and no...the timing curves are way different between auto and marine. The marine ignition system will reach full advance at 3000rpm and has a nice gradual advance curve where as a an automotive distributor reaches full advance around 4200 rpm and has a much more agressive curve from 2000-4200rpm. You will probably be able to make it work but you will not be happy with the performance and you will most likely be getting estimation on the top end because an automotive advanc generally will advance to 32? max vs. a marine curve reaching a full advance of 26?. Is your ICM an old or new style the new style is about 1.5x3" the old style is a 4"x4" box. I have a ICM from a 94' 4.3L...new style

Re: Switching to a HEI ignition on 4.3L Mercruiser

Make sure your hall effect pickup is not rusty and is functioning correctly before replacing the ICM. This can easily be checked with a lab scope. This pickup causes most of the problems with the thunderbolt ignition system...$50 from Sierra

Re: Switching to a HEI ignition on 4.3L Mercruiser

winterfunguy said:

Yes and no...the timing curves are way different between auto and marine. The marine ignition system will reach full advance at 3000rpm and has a nice gradual advance curve where as a an automotive distributor reaches full advance around 4200 rpm and has a much more agressive curve from 2000-4200rpm. You will probably be able to make it work but you will not be happy with the performance and you will most likely be getting estimation on the top end because an automotive advanc generally will advance to 32? max vs. a marine curve reaching a full advance of 26?. Is your ICM an old or new style the new style is about 1.5x3" the old style is a 4"x4" box. I have a ICM from a 94' 4.3L...new style

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Mine is the thin smaller one with one plug with 8 pins. Is their a different year or part number that will work? Thanks for your help...

Re: Switching to a HEI ignition on 4.3L Mercruiser

Recount the pins...should have 6 pins

Re: Switching to a HEI ignition on 4.3L Mercruiser

chop413 said:

Has anyone done this before? My ICM is bad and I don't want to pay $500 for a new one.
I can buy a new HEI aftermarket distributor for $180 with built in coil. Any suggestion?
The motor is a 96 Mercruiser 4.3LX

Click to expand...

Has anybody done it? Yep. Did those people care about their lives, or the lives of their passengers? Apparently not...
Automotive distributors don't belong in boats. H.E.I. is not U.S.C.G. approved. You run the risk of the distributor lighting off latent fuel vapors in your bilge, and I highly doubt your insurance company is going to cover anything if thats what happens...

Consider this;
http://www.michiganmotorz.com/delco-voyager-marine-electronic-distributor-p-121.html

Re: Switching to a HEI ignition on 4.3L Mercruiser

I checked it 1000 times it's 8. The brand name is NipponDenso part#131300-2360