Mercruiser repower with a 4.3 EFI

[get-r-done]

Couple weeks ago I ask about doing a repower on a 19ft rinker which had a 3.7l inline 4. Was considering a 3.0 however everyone suggested a 4.3 due to the gearing in my outdrive. I have since purchased a used 4.3L which came from a boat that had a bravo2 outdrive. Since I am keeping my alpha 1 gen 1 outdrive I am faced with some obstacles. The 4.3L is an EFI motor 2000 model year. I am being told that the ecu will need to be reprogrammed to allow the shift interupt functionality. I have found a shop in Arizona that can do this for a hefty fee. Does anyone have experience with this? There is only one part number for the ecu for that motor be it alpha or bravo. I am being told that mercruiser put code into the module depending on application. Does this sound right?

 

[mylesm260]

Re: Mercruiser repower with a 4.3 EFI

Reprogramming should not be necessary.


The shift interupt works by temporarily cutting power to the ignition coil (or the signal to the coil)

I"m running automotive EFI with my setup, and all I did was wire a relay in series with the +12 to my ignition coil.

You put tention on your shift cable
It triggers the switch
The switch causes the relay to "open"
The "openning" of the circuit cuts power to the +12 side of the coil
Your drive shifts
The switch springs back
The relay "closes"
Your ignition coil continues to fire


If you are running coil on plug (not sure about 2000 model year) then you will have to find the +12 supply to all the coils (should be one wire somewhere in the harness)



Make sure you use a proper relay pigtail and a good water-proof relay. You don't want to intoduce any potential electrical sparks into your engine compartment.

 

[get-r-done]

Re: Mercruiser repower with a 4.3 EFI

Call me dumb, because when it comes to this stuff I certainly am..... Isn't that what the interupt switch on the shift bracket does anyway? It shouldn't have anthing to do with the ecu. Basically doesn't the interupt switch ground the coil briefly while shifting occurs?

 

[skyking_22]

Re: Mercruiser repower with a 4.3 EFI

I just purchased an EFI conversion kit from an online vendor for 1900.00. I repowered my 5.7L 350 and it was very easy. All parts were included. As for the performance I show that I am using 7GPH less at 4000 RPM now and I got a whoping 5400 RPM's out of it and top speed of 49MPH. Before the most I could get on a clam day with the wind to my stern was 40mph. I love it.

 

[Bondo]

Re: Mercruiser repower with a 4.3 EFI

and I got a whoping 5400 RPM's out of it and top speed of 49MPH.

Ayuh,....

You need a Bigger Prop....

 

[Don S]

Re: Mercruiser repower with a 4.3 EFI

Shouldn't be any reason for a relay on your engine. If this is a TBI type EFI and has the EST distributor, just locate the white wire that goes from the ECM to the Distributor. The shift interrupt switch goes in that wire.
I would suggest you post your engine serial number just to make sure what you have.

 

[get-r-done]

Re: Mercruiser repower with a 4.3 EFI

Engine serial number is OL651284

 

[newport dave]

Re: Mercruiser repower with a 4.3 EFI

The Merc MEFI3/Alpha equipped engines (like this one) did use the ECM for power reduction during shifting. They reduce the IAC setting and retard the timing instead of interupting the ignition reference signal. But it's not a big deal, as suggested there are still a number of ways to do it.

 

[Don S]

Re: Mercruiser repower with a 4.3 EFI

One nice thing about doing it the way the Merc manual shows it, is that it makes it a lot easier for a tech to check the EFI system if the owner can't . It's a time consuming process for a tech to try to figure out some DIYer wiring jobs. And I have seen my share of them.

 

[get-r-done]

Re: Mercruiser repower with a 4.3 EFI

I appreciate everyones responses. Let me better understand this. Can I just connect the interupt switch to the coil wire to briefly ground the signal during shifting? Is it that easy?
Or
Since there is only one part number for the ECU can I expect that my ECU has the programming necessary to do power reduction during shifting, or did they put different code in for say a bravo vs an alpha? If it does have the proper code or I have it reprogrammed, where do I connect the interupt switch at that point? The information from the ECU is Part# 862148T3, it has coding on the back side of 1623699 and 86699KA0028800. There also is a white tag on the side with BC30, which my understanding is that is the code level loaded into the module. I am not sure it would matter but the shop willing to do the reprogramming ask for the distributor type which is a Thunderbolt 4.

 

[Don S]

Re: Mercruiser repower with a 4.3 EFI

I am not sure it would matter but the shop willing to do the reprogramming ask for the distributor type which is a Thunderbolt 4.

Thunderbolt IV ignition has NEVER been used with EFI from 99 or 2000

You are trying to do a lot of off the wall stuff, not necessary to use the shift interrupt switch. Why don't you just hook the white wire to the SI switch like Merc does, and don't complicate things and make them unusable. And how about a picture of your distributor, because you really don't have a clue what you have or what to do with it.

 

[get-r-done]

Re: Mercruiser repower with a 4.3 EFI

Don,
If all that is necessary is to connect the white wire enough said. You are correct I don't have a clue which is why I am asking here. I am simply trying to avoid an unnecessary reprogram which cost $400.00. As far as the distributor perhaps I misunderstood what the mechanic told me today. He also is of the opinion that all is necessary is connecting the SI switch. We are just trying to make sure.

Again thanks for your help.

 

[Don S]

Re: Mercruiser repower with a 4.3 EFI

You have too much BS in your head, you don't need to ground the coil like mylesm260 mentioned, you don't have an automotive system like he does.
You are the one trying to complicate it.
Like I said in my first reply. Put the shift interrupt switch in the white wire that goes between the distributor and the ECM and it will work just like Merc designed it. What is so hard about that?

 

[get-r-done]

Re: Mercruiser repower with a 4.3 EFI

Don,
I don't know what I did to pee you off but I obviously did. I will try and get the BS out of my head. You should try to get yours out of your fingertips.

Thanks Again.

 

[get-r-done]

Re: Mercruiser repower with a 4.3 EFI

BTW, this is a thunderbolt IV distributor. Looking up the part number in the manual brings me to this description.

Distributor - 805185A37.

* Fits GM V-6 with Thunderbolt IV ignition
* Bullet connectors

Don't know if they used them or not for that year but that is what is in it.

 

[get-r-done]

Re: Mercruiser repower with a 4.3 EFI

Perhaps some more book readin and less grouchy remarks are in order for some.

 

[JustJason]

Re: Mercruiser repower with a 4.3 EFI

That's no TB4 distro....
Can't say what it is from my house.... but it's not TB4....

and don't say more book reading and less grouchy.....

All those books everyone reads..... Don's been around long enough he might as well have written them. He's here to help just as much as everyone else is.
If you want to play odds.... if you do what he say's 98% of the time you'll be correct 98% of the time....

 

[newport dave]

Re: Mercruiser repower with a 4.3 EFI

That's no TB4 distro....
Can't say what it is from my house.... but it's not TB4....

Well, that IS a T-bolt IV distributor.

Don is correct that they never used the T-Bolt IV distributor on any EFI engine '99 or '00, or any other year for that matter. They did use the T-bolt dist with no ignition module (meaning it's not a IV or V, since the igntion module is what determines if it is a IV or V) , in the small block EFI/MPI engines in '99 and '00.

What you got there is a T-Bolt distributor with a T-Bolt IV Module that came out of a pre '95 carbed engine.

 

[JustJason]

Re: Mercruiser repower with a 4.3 EFI

i stand corrected then..... i'll have to run through my ignition ID book and make a correction

 

[Don S]

Re: Mercruiser repower with a 4.3 EFI

Somebody better show me a service manual that shows ANY EFI engine using a Thunderbolt distributor. They all used either the Delco EST (Early) and the later used the composite one (for the life of me I can't remember the name) with the flat cap.