MEFI-4 Questions
 

What is the difference between MEFI 3 and MEFI 4? I have acquired a new MEFI 4 computer and harness but my other setups are MEFI 3. Can these 2 systems work side by side? The last question is what factory marine engine used this system. One of the brackets has dark metallic gray paint and the injector connectors are different than the ones I have seen on most Merc units.

Anyone want to trade a MEFI 3 with 500EFI style harness for this one?

Re: MEFI-4 Questions
 

The MEFI3 and MEFI4 could work "side by side" as long as they were both programmed for the same engines. It sounds like you are trying to use a mismatched ECM and harness, possibly from a Volvo (grey paint). You should not attempt to use it.

Mercruiser never used MEFI4, except as an aftermarket replacement for failed and no longer available MEFI3 units. They sell the MEFI4 conversion as a kit.

Dave

Re: MEFI-4 Questions
 

i am not certain that is correct. i was trying to buy a used efi system as a spare and the ecu #s were different. i ended up calling some engineers at delphi who suggested that , in my case, the ecus were different but ALSO made the observation that the pin outs on the 3 vs the 4 systems were different and that a 4 ecu wasn't going to work in any respect if plugged into a 3 harness. my impression was that the 4 harness is comprehensively different from a circuit stand point. not offering this as authoratative but thats what they told me 30 days ago.

Re: MEFI-4 Questions
 

Thanks for the comments. Sounds like I should be able to get this worked out with some connector and program changes. The harness and ECM are from the same engine and I would think that the sensors should be the same but the connectors may be different.

To keep my engines the same, I may just sell the MEFI 4 with matched harness and try to find another harness that works with one of the many MEFI 3 computers that I have.

Re: MEFI-4 Questions
 

merc uses mefi 4 because there are no more mefi 3 boxes to recal or reprogram that why merc went to the mefi 4-you can use them side by side with mefi 3-all the performance racers and aftermarket companies gobbled up the mefi 3 boxes-also the mefi 4 box comes with an external coil driver and mefi 3 is built in the ecm

Re: MEFI-4 Questions
 

What's the part number on the back of your mefi4? I have a new mefi3 harness. What engine are you dealing with?

Re: MEFI-4 Questions
 

you cant use a mefi 3 harness on a mefi 4 ecm-you need to get the entire mefi 4 kit which comes with an external coil driver and all harneses-

Re: MEFI-4 Questions
 

RC572, the # on the MEFI4 is 12569494 It also has 869494KA22980008.

My engines are using the ASM injection like the HP500EFI. One was a complete package that I got from ASM for a single engine boat that I had several years back and now I am building a second for my current boat from parts that I have collected.

Call me if we can do anything.

Todd Howerton
Outlaw Disc Brakes
770-844-1777

Re: MEFI-4 Questions
 

Mefi4 12569494
Mefi4a 12575479
Mefi4b 12584052

I'll give you a call.


You can re-pin a 3 harness to work with a 4 and vica-versa

Re: MEFI-4 Questions
 

Hope you dont mind if I butt in with a question, I have a 2000 502 MPI, sent the ECU (Mefi3) up to get reprogrammed over the winter, boat won't run this spring. Ran fine last fall, it fires right up then dies. Swapped out a friends ecu and it ran fine. Sent the ecu back for a completely new program and it does the same thing. I am told that my ecu must be bad and I have to buy a new one and send it up again. WTF?
How could this happen?
Do you think this one is toast or should I try somewhere else. The ECU was sent to a top-notch builder but I am a little hesitant to buy anither and send it up there.
Thanks

Re: MEFI-4 Questions
 

Sorry to bring up a old post but did you repin to the MEFI-4 or not. If you used your freinds ECU which was a three and it worked just fine I have to wonder why. I am making a change right now with my ECU and I m just wondering what to expect.

I have a bad MEFI 3 it is doing the same exact thing

Are you in Alabama by chance?

Jeff

You can not just plug and play from MEFI 3 to MEFI 4 - There is a harness adaption that comes with MEFI 4 that is added on top of. Also there is not just one MEFI 4 for all apps.

I asked this before is this Dave _ N guy around - heck he is pretty sharp about this OEM EFI and MPI systems. I came across a couple of other posts from him while searching for a post of mine last year.

I have a couple of sheets of paper that have the pin to pin conversion for 3 to 4/a/b.repinning wasn't all that bad.

I have a 3 & 4 for sale

4b?

no............... isn't the difference, the B has a built in power ( surge ) protection ?

I am in north AL.

I believe he has passed or that what was said on another site yrs ago, Yes he had a very firm grasp on mefi in almost every aspect.

Oh I had no idea at all. It seemed he liked to help a lot of other boaters out. One of these days I will read thru the older posts as you could tell he was very well trained thru the OEMs on the fuel injection side. Seemed to be pretty darn sharp as I respect that. I was just trying to see if we have ever crossed paths somewhere especially in any of the OEM schools or however.

Do you know what happened ?

Did you ever own a Donzi Minx?

Jeff

No I never even owned a Donzi of any kind. Why do you ask ?

It was for Steve from Alabama.
The quote option wasn't cooperating.

Jeff

When i converted my mefi 3 to mefi 4 i was told it was just a matter of repinning the harness. A "expert" at this did it in mi, said he did it all the time. When done when the key was turned on dyno it filled all the cylinders with gas. At that point we bought a new mefi 4 harness after butchering my virgin mefi3 harness, fwiw.

^^^^^ I totally agree and that's why I posted its not a simple plug and play without the added harness adaption that comes with the MEFI 4 conversion.

I said this a million times in another thread about the kid with the Volvo Penta who did not have it installed with his MEFI 4 conversion. Just saying. There is a reason why the harness and that adaption comes with MEFI 4 conversion.

B does not mean it is surge protected but it's a nice thought.
The 3 harness can be reworked to meet any of the 4 family of ECU, the degree of difficulty is related to your patience and having the proper documentation.

Anyone happen to have a copy of a pinout diagram for the 3 and 4 units they could share?

Do you still have a 4? Maybe a 4a?
Thanks

Do you still have a 4? Maybe 4a?
Thanks

no

Still have the mefi3? If so please call me been looking for one 207-837-4692

yes 16236999

Give me a call or text whatever is easier 207-837-4692 Thanks