MEFI Programming
 

I have a Mag 350 MPI. I’ve got the engine torn down. Is it worth stroking to 383?
Would I see any noticeable speed gains?
If I were to stroke it to 383, would I be able to keep my current MEFI 3 controller and just have it reprogrammed?
How much would that programming cost?

What boat and how fast with current power ?
will you or someone else he able to program it in the boat on the water ?

seem very unlikely. even if you go from the 5.7 to the 6.2, you gain maybe 2-5 mph top end.
I have 2001 Merc 350s MEFI3s (new base engines in 2021)

top speed on my formula 292 with twin 350 is 68 mph.
twin 6.2s is like 72...

so... meh. I run WOT maybe 1% of the time?

it’s a 1969 Formula 233. I’m restoring g it so never had it run with this power. I’d have to have someone else do the programming. I’ve never done anything like that.

The problem your facing with the mefi programming is no one including mefi burn has ever figured out the unlock codes for the factory 5.7 ecm so any tuning done would be starting over from scratch. Since theres not alot of NA 5.7's with mefi3 hopped up, I highly doubt anyone has a "canned" tune either that would be remotely right. Not saying it cant be done but I 100% would say it needs to be at a minimum done on water WITH 02 feedback from exhaust and really/ideally done on a dyno. I do both, Im in michigan, dont know where your from but I tune mefis all the time, Smitty

thank you. I’m located in Massachusetts.

Yes you would be able to keep your current MEFI 3 controller. Yes you would be able to have it reprogrammed, but there are some catches. The password to unlock the MEFI 3 needs to be acquired IF you want to modify the original tune. I was under the impression that Bob at MEFIBurn had some codes for MEFI 3, but I could be wrong on that account. The other option is to wipe the original tune and start from scratch but this can be highly problematic if you don't know what you are doing. The most realistic option is to get a tune for a MEFI 3 for a 454 and transpose to a 350/383. Basically you would need to scale the fuel tables for the injector size and fuel pressure.

There is another option that may cause some here to have a stroke at what I'm about to suggest. Assuming you are only going from a 350 to a 383 and not extensively changing a bunch of other stuff then begin by running the new motor with the original factory tune. YOU MUST DO SO WITH WIDEBAND installed and monitored. I say again YOU MUST DO SO WITH WIDEBAND! The factory 350 tune will successfully start and idle a 383. The only major parameters you alter in MEFI tuning are primarily 1) fuel tables (BPW vs MAP vs RPM) and 2) spark tables. Theres a whole bunch of other stuff in the MEFI tables that in most cases does not need to be tweaked, at least initially. Now I am NOT saying just run it as is a 'send it', but rather do incremental tuning explorations under no load or mild load and see what the AFRs are doing. I would start this on a test stand which can be done fairly easily at your home or shop. You might find that there is enough slop in the stock tune to handle a 383 for the parameters you boat in. I cannot guarantee that but it is possible. The factory tunes are slightly rich and it is possible the AFRs would still be reasonable. There is not a major gap or change is basic small block timing between the two motors either. Both are going to have about 8 deg BTDC base timing at idle and roll up to 32-34 deg max for WOT.

Let me give you a real world, first hand account example. I had a bone stock 350 Mag/EFI MP motor (1995 MEFI1) that got turned into a 377, with bigger cam and heads. Started up and idled first try on a bone stock factory tune. Idle AFR was about 12.4-12.8. From there I kept it simple and made one change at a time and checked the results.

The cost of tuning can vary quite a bit. The most cost effective method is to get MEFIBurn and do it yourself on your time table. That's what I did. It will be intimidating and possibly overwhelming at first but if you immerse yourself in the simple basics it can definitely be done.

I think its worth it to stroke the motor since its already torn down. You will get some extra cubes and torque, all of which boats tend to appreciate. Speed gains will depend on how amped up the 383 is. I think 2-4 mph is a reasonable gain for a mild build.

can also throw an intake and carb on it old school and it will run great many fishing boats have been retroed because a carb(eldebrock 1409) almost always idles better for 6 to 8 hrs also you can make tiny throttle adjustments to get the 1.6 - 1.8 mph troll speed as you head into the wind or downwind idle rpm is most often 500-650 rpm range a few go below 500 but i dont like to i try to keep 600 or above to keep things circulating the problem with the 6.2 in the fishing world is you have to really wind them up to get the boat going they make power at higher rpm at least in the inboard world

Bob has told me they have never spent time to crack the 350 5.7 ecm codes when I asked fwiw

This would be a great alternate plan.

Good to know. I seem to remember he had a few, but not all. With enough MEFI 3 tunes floating around it would seem easy to load a big block tune and scale back the BPW table. All the other scalars and constants rarely need to be touched for initial tuning.

On another thought, assuming the 'new' 383 runs too lean for his taste with the stock injectors and fuel pressure, rather than jack fuel pressure up just install slightly larger injectors. Say go from a 26 lb injector to a 32 or 36 lb injector. Timing table and all the others scalars could remain untouched and the larger injector could be sized to the increased displacement. Conceivably the tune would never need to be modified.

Funny story about "tuning" a 5.7 TBI: A good friend whos retired had a fishing boat, had a 5.7 tbi mefi3 , sits down under floor with giant hatch you remove. Calls me up all in a panic, says he has boat sold but suddenly it wont run right and guy wants his deposit back. Proceeds to tell me the most convoluted story. So he tells me he always ran a certain prop and it never quite revved where its supposed to, guy was buying it so he put a slightly smaller prop on it to "impress" him, proceeds to tell me that it hit the rev limiter and broke up a little and has never ran right since then, they been paying to have it worked on and seems to be no fix. so he says they took it to a local marina next to the boat launch in a nearby town, they determined it needed a fuel pump and charged him 1000+ $ to change pump and scan it. So after they did that, it ran EXACTLY the same. So they told him that these efi systems have a "hard" rev limiter and once you hit it , sometimes you have to have a efi guy go in and clear it (you cant make this **** up). So, I grab mi tuning laptop, mefi burn cord, some hand tools, a few sensors etc and meet my friend at docks, on way there I call bob at mefiburn and ask him if they ever figured out any unlock codes for any small blocks as Id like to pull the tune off for future reference, tells me nope. So I get there and I take one look at the motor and see the tit for the map sensor is broke off and WTF, the hose going to map sensor is plugged onto a exhaust riser on a little barb. I laugh and tell him well, this will be a two minute fix, I wont even need to scan the data with laptop. I pull out a new map sensor I brought, I install it, attach the hose back to the vacuum port on motor and I ask him who the fawk has been wrenching on this?? proceeds to tell me the fuel pump, hard rev limiter story. Then he tells me oh yeah, the changed the riser gaskets two. So the incompetent marine "tech" BEFORE it had problems did riser gaskets, broke off the map sensor, attached the signal hose to some random fitting on a exhaust riser .
So, new map sensors in, we take it for a spin and NO, its NOT fixed, its back firing and breaking up under a load. So I ask my friend : tell me EXACTLY everything thats been done to this, every detail. He says oh yeah, my neighbor was trying to help two so he pulled the throttle body off and "cleaned" it. So I plug mefi scan in, I sweep the tps and lo and behold its frozen in time, does not do anything thing as far as voltage change (should have done that to begin with). So I ask him, did you guys take the tps off, he says yeah, either the neighbor or the guy at marina did. Well, they put the flat part of shaft in it wrong and ripped the guts out of it.
So, we leave the boat at dock, run to a auto parts store, buy a tps for some TB 5.7 version for a Chevy van or something and boom its fixed. I ask my friend, you PAYED the guy at marina next door to scan this and he didnt see any of this, unbelievable!

Amazing story. Can’t believe number of people that hack their way through, lie to customers, and steal money. Sad.

What I CANT believe is they misdiagnosed the fuel pump and failed to see obvious problems on engine and didnt see them scanning it either Im not some
merc certified tech' but within 15 minutes I had it completely figured out, LMFAO!

Classic. Glad you helped the guy out!

Hey ArticFriends, Sorry to hijack the thread. Are you still running your MEFI ECM? Any tiips on how to use MEFI Burn?
I would send you a message but I don't have enough points.
Thanks, Don

Contact him here Steve Smith good dude
https://smittysengtrans.com/

[QUOTE=F-2 Speedy;4921179]Contact him here Steve Smith good dude


Thanks!

I have been using MEFI Burn since 2010 for my own application. Can offer some limited guidance as needed.

Throw some Holley on it, it`s not dinosaur software like the Mefi stuff and significantly more user friendly and intuitive.
I couldn`t figure out mefi.. thank God for Eddie Young and Steve.

Mefi
 

Trash, Thanks for the offer. I'd love to hear more about it.

Can you message me and I'll reply. I don't have the posting cred yet.

Thanks,
Don

Mefi
 

Speedy, Thanks for the referral. He called me and we had a great conversation.

Definitely a great Dude.

[QUOTE=F-2 Speedy;4921179]Contact him here Steve Smith good dude

Mefi
 

Trash, Thanks for your response. Turns out I can't even read private messages. I'll get it sorted later today

you have 10 post so you should be able to read and send pm's and pictures / links

[QUOTE=Donski;4921403]Speedy, Thanks for the referral. He called me and we had a great conversation.

Definitely a great Dude.

Was good speaking to you, keep me in mind IF you do need injectors flowed AND cleaned as I offer that service on top of all the other dynoing, tuning etc, Smitty