mefi4b vs mefi 3
 

I'm hoping to go to the dyno fri at Crocketts,I have been using a mefi3 to run my injection until now,My new cam and valve train (thanks to RMbuilder) is expected to pull past 6000 rpm's. A mefi3 is not capable of supporting fuel tables or programming past 6000 rpm's,I recently bought a mefi 4b that I plan on using,is there any thing it won't do or will be a problem compared to my old ecm other than re-pinning some terminals in my harness? I have been told it will support fuel tables/programming well past where I need to run my motor,Smitty

I have a mefi4 and I think it was programed by Arizona Speed and Marine, if that helps any.

I guess my question is what is the diff between a mefi 4b and a mefi4,Smitty

I purchased the 4b and the ingenious software from AZ Speed and the fuel table in the software goes to 9000. I didnt buy the 4b wiring harness so had to re-pin my MEFI 3 harness to work with the 4b (fun times).
Havn't run the boat yet since the change, but hope to this weekend. Also have a wideband and pyrometer to help tune while running.
Turned the key after getting everything wired and so far all seems to be ok as I have no codes and everything that happens with just the key on still worked. Will be starting on the hose before heading to the lake just to be sure.

I havent posted much here, but have gotten a ton of info from the site and hopefully can contribute some with this.

The biggest diff is in the rpm range and boost amount. The mefi 3 is limited in boost and rpm (rpm 6300, boost app.14 psi), where as the limit in the mefi 4 is not an issue anymore since it is so high. (rpm 9000, boost app. 28 psi) If it is a supercharged motor, than you will have MUCH better control over the fuel curve with the 4 when under boost. The 3 only uses a multiplier to control injector times when under boost, where the 4 has seperate boost tables. Hope this helps, Eddie.

Thats what I wanted to know,I got a killer deal on 2 mefi4b's in the past 2 weeks on E-bay,brand new never been programmed> I was under the impression though that the mefi3 was only good to 6000,not 6300,so I guess I learned something else too. If I get my extra throttle body back tommorow I plan on a dyno pull with my 540 fri with blower disconnected to see what it makes N/A,Smitty

Smitty, yeah, it is definitely 6300. I've hit it a few times:D Glad I could help. Good luck with it, Eddie

I wish I had known the mefi3 could have went 6300 because we (me and Crockett) programmed mine to go 6000 on the dyno last time and I have been on rev limiter quite a few times. I would have had him take it to 6300,thanks again,Smitty

You can set the rev limit to whatever you want in the MEFI 3 or any generation of the MEFI controllers. For example, the MEFI 1 spark table stops at 3600 rpm and the fuel table stops at 5200 rpm, yet you can run the engine much faster if you want, it will just use the last value at the top of the table.
Bob

If you don't mind me asking, where do the tables end for rpm on the MEFI 3 and MEFI 4 ?

Thanks again for all your very valuable info.