pachangalpina

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?

Dave_N

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

stevesxm

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.

pachangalpina

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.

mr mercruiser

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

RichardCranium572

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

mr mercruiser

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-

pachangalpina

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

RichardCranium572

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

Pete280

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