I am in the process of doing a rebuild and am wondering the longevity of the mefi 3 ecm. Mine is a 2000 on a 502 mag mpi. The Holley HP looks like a slick set up but I am concerned about hatch clearance and would like to keep a stock appearance. Any insight would be appreciated. Thanks in advance.

Just my opinion here, but if staying stock, the old MEFI is wonderfully simple and reliable for marine use. The Holley, while a great system, will do very well to have the reliability record of the MEFI. For how many zillions of these that are in service, it is pretty rare to find one that has shot craps for no reason.

Ive had my hands on at least 100 mefis in past 15 years, saw a guys boat that killed 2 mefi-1s on same motor (30 hrs apart), I blame something in his wiring. Saw 1 mefi4 that would not turn on his fuel pump relay no matter what we did so we triggered relay on a different way, sold 1 mefi3 with a 500 efi tune that I loaded on it to a guy from Florida that thought he had a bad one (never heard back IF that fixed his issues) that's IT. A EX-member from here (BUP) has posted pictures of stacks of bad "mefis" he's repairing, looks like a EPIDEMIC looking at his post but I personally haven't found that to be the case. Now, a mefi3 is potted, Ive seen them where they were under water and still worked afterwards, I don't think a Holley is necessarily as sealed /rated for marine use and I think over time theirs MORE of a chance for one to fail then a MEFI. I HAVE also seen harness problems on a few mefi boats too BUT unless it was under water in Saltwater can easily be traced out and repaired, Smitty

Thanks for the replies. That makes decisions a lot easier !

My opinion if you need to tune it and want to learn EFI go Holley. (The HP and Dominator are aluminum cased and fully potted, Terminator plastic and not potted) If you don't need to pay for someone to tune it keep the MEFI.

I've run my original MEFI 1 for 25 years and literally hundreds of tunes loaded and downloaded. Zero issues, not one. I'm not sure how much more bullet proof it can get.

Anyone hear of a mefiI that will not send a signal to the IAC? IAC is good and wiring checks out.

Padraig

driver in the ecu is blown,,ie a transistor.

I have a bad MEFI 3 with that same exact issue. Anyone know whether this can be repaired?

I asked BUP since I know for a fact he repairs a lot of ECM’s. He said if the IAC drivers were available he would be able to repair the MEFI 3’s. MEFI 4’s use a different IAC driver than MEFI 3’s. But the same goes for the MEFI 4’s if you can find new IAC drivers for that ECM he could repair them also. For 2020 the MEFI IAC drivers he could not find any new and he has no more in stock either per his words. Anyhow I thought I would ask to see what he had to say.