454 MAP to 502 MAG ECM remap question
 

Some of you may remember my situation. I have a 1996 Crownline 225 CCR that had the 454 MAG MPI gen v engine. It spun a bearing and cracked the block and I was going to rebuild the engine but came across some 502 Mag MPI gen vi engines. I have the engine ready but my question is about remapping the ECM. I have done some research and found that Whipple can retune the computer to a 502 increasing the advancement and rev limiter but I have to use 91 or better octane and at the cost of $600. All i really want to do at this point is simply remap it to a 502 mag MPI setup. I called the local Mercury dealer and they say they cant do it anymore. Does anyone know anyone that can do this as it should be a simple $100 remapping? I have another 502 I'll build and then remap but I want to get back on the water pretty quickly.

The next question is the Gen V has a MEFI 1 ECM but the engine is a Gen vi which I believe came with the MEFI 3 ECM. However I believe the 502 MAG MPI was also offered in Gen V the only difference being roller rockers? So I guess my real question can I get the same tune as the Gen Vi to work on the MEFI1 ECM or will a Gen V 502 remap on the MEFI 1 ECM work for the Gen vi motor.

I am assuming you are using the 454 ecm and intend to use that on the 502s. Get the motors assembled, wired and plumbed and run them on a test stand (preferably) or in the boat utilizing the existing ECM tune. The motor will start and run and do so safely at idle and no load with the original 454 tune. You would need to have wide band O2 installed to see what the AFRs are prior to doing more tuning. Your best option is to get MEFI Burn and dial the motor in yourself. You will not need many changes or as much as you might anticipate.

It is NOT difficult and you would mostly make minor adjustments to the fuel and spark tables.

The motor does not care what version MEFI is running it nor does the MEFI version care what motor it sits upon. The motor only wants to see correct fuel and spark. If you have a a MEFI 1 with a 454 tune use it on the 502 as I stated before. The MEFI 1 is very simple and easy to work with, but lacks the fidelity of later MEFI units, or any other later ECM platform. For a basic N/A motor the MEFI 1 is fine. MEFI 3 has more fidelity but also takes much longer to load the tune.

A MEFI 1 tune will not load on MEFI 3 and a MEFI 3 load will not load on a MEFI 1.

IF I was you, I would use the MEFI 1 and tune it myself.

I don't believe any of the 454 or 502 black motors came with roller rockers. They would not affect the tune at all assuming the same ratio.

throw a custom carb and high rise performance intake on it and call it a day. Also install current fuel delivery system set up and call that a day. How long will the mefi 1 last and if you have the VST set up that is on borrowed time as well. Prob doing these installs you can get closer to 1 hp per .

Thanks for the input guys but I plan on keeping the fuel injection and I really dont want to tune the engine myself since I dont have the software and I dont know what Im doing. For $400 Arizona Speed says they can put the 502 tune on the 454 ECM MEFI1 computer but will it work? A intake and carb and or software all cost more money then just reflashing the computer if it is possible. It seems to me this should be a easy thing to remap to a stock 502 EFi tune as Im sure this motor was also offered in GenV. It has the exact same heads, intake, crank, rods, and so on. Surely they made a VST 502 motor. Im not looking for top end or performance. Im simply trying to get back to the water.

That being said I dont know if the roller cam in this motor is actually any different and could change how the tune operates.

The MEFI 1 will be fine. It is simple and robust. I have over 25 years of use on mine and 100's of tune installs. VST can be rigged with fuel return to tank and a new internal gasket kit if needed.

It is an easy thing to reflash the MEFI 1 to a 502 tune. You will spend $400 for AZSM to reflash the ecm or you can spend $600 and get the software and do it yourself. IT IS EASY! Plus you can tailor the tunes as much as you want on your time frame. I would run the motor on the existing tune FIRST then reflash/tune as necessary.

I rebuilt the VST last year for $50, new gaskets and pump, If needed it looks like the MEFI can be had for $500 if needed but I have a good one. Surely there is a easier way to get this computer tuned then send it to one of the online guys that charge for a performance upgrade. Mercury must have had a way to reflash a stock tune into the computer in case the ECM needed to be replaced?

Ok you may have sold me on that one. If its easy to as selecting the stock 502 tune Ill buy the software and try it myself. Where can I get this? Whats it called? I would like to change the rev limiter and idle a hair lower if possible and look at PID data if possible.

Decided to call one more boat store and they think they can do it for $65. The key word here is they think. Told me if it locked up my computer Id have to buy a new one. Has anyone ever had one lock?

Its not a selectable thing, unless you know someone with a stock 502 VST tune (maybe Articfriends or Young Performance) then you have install O2 bungs, get a AFR meter and buy MEFIBurn software.

The MEFI 1 is not locked, and since these guys don't know that don't let them touch it.

Thats what Im afraid of!!! So since its not selectable and Im not installing O2 sensors and buying a AFR meter then Im back to sending it to Arizona or Whipple for a stock tune replacement. There has to be someone that I can send this to for a simple reflash right or are we way over on the age that no one is dealing with them anymore?

My guess is Eddie or Smitty will have a base tune. I probably have a base tune on the MEFI 1 pulled off my motor (502 mag MPI VST) when I had the motor re-powered using a MEFI 3. The issue I have is figuring out how to power it up so I can download the tune to a bin file using my copy of MEFIBurn. I have a MEFI 1 harness, just would need to sit down and figure out how to do it. Not rocket science, just something else to do

That explains why these shops charge so much. If someone has a good base tune I'll buy the software BUT I just dont want to be stuck buying 93 octane using a performance tune. I do want to adjust the rev limiter up to 5400 but just not worth paying $600 and have to keep messing around with a tune when I can be on the lake cruising. Idealing it would be nice to have both performance tune and base tune to switch back and forth.

Don't think its a switch, it would have to be reloaded each time. No need to switch and should not be switched (IMO) even if you could. The motor should be tuned for optimum performance and then leave it alone

I dont disagree but whipplecharger says they can provide better performance on low and midrange though tuning provided I use higher octane which sounds like a fair trade off, if I had the software I'd reflash the computer if I was running cheap gas and was gonna go through a couple of tanks in a weekend but if im out hotrodding I'd put back the whipple tune.

I keep thinking there has to be someone in Chattanooga that can base tune this. There are tons of offshore type boats here and there has to be a performance marine or dyno shop here. Just cant seem to find anything in google.

I'll be happy with a stock tune but if I have to spend $500 for a performance tune I think I might just try the 454 mag tune. Literally the only difference is cubic inches I cant see the computer knowing that much of a difference.

I will touch on a couple of points and reiterate some others.

I would not raise the rev limiter. You would likely be exceeding max hp curve and not see any improvement in performance. Heads and cam might benefit from an increased rev limiter but not in stock form. I also would not alter the idle unless it is way off.

The MEFI controller only holds one .bin file at a time. You cannot 'switch' between tunes on the fly. You would have to load the tune each time you want to make a change. A MEFI 1 loads in about 3-5 seconds. MEFI 3 takes a little over 2 minutes (PITA).

Run the motor with the existing 454 tune THEN see where you need to go.

Gen V 454/502 had 48 lb honda/keihan injectors, gen VI had maghetti marelli 45/46 or so lb so possible a mefi1 with original tune will be 3 or 4% leaner but I wouldn't get crazy worrying about it as mercruisers are pig rich from factory anyways. I sent you a PM on tuning your ECM, Smitty

So this makes me wonder if the tunes from the 454 mag mpi to the 502 mag mpi are any different. They both, in Gen V used the same injectors. However, Im running a Gen VI 502 longblock so the cam would be different since its a roller and from a MEFI 3 boat. I have a bad feeling I may have messed up putting a 502 GenVI long block in place of the 454 Gen V. Noone seems to know if the tunes were any different from 454 to 502 and GenV to GenVI so I have no clue which tune to offer the motor. I do know the GenVi motor used the same internal parts minus the pistons and cam.

To the best of my knowledge the Mag/EFI motors were all hyd roller cams. I would need to dig out my literature, but I know the small block motors were. Don't over think the GenV and Gen VI stuff. Run the 454 tune on the 502 FIRST. Then see what needs to be done. Like Arctic said the factory tunes are pretty rich/safe assuming your fuel pressure and injector sizing is factory spec.

I have personally run a bone stock factory MEFI 1 tune from a 350 Mag EFI/MP motor in a 377 stroker, WAY bigger cam and heads and it lit off on the first try and idled on its own. AFRs were in the mid to high 12's at idle on the modified motor and stock tune. Hardly dangerous as a starting point. I am confident you could do the same. Either tune the 454 .bin yourself (requiring wide band which is easy) or hit up Bob and MEFI Burn or for a 502 tune.

Nope. Even the Gen V 502 MAG MPI was flat tappet.

Thanks for the clarification. You forced me to dig out the old brochure. The verbiage in the paragraphs in the 1995 Mercury brochure would lead one to believe they were roller camshafts, but the actual motor listing shows only the small blocks and a few 'blue' motors as having a roller cam.

Regardless, for the OP, the difference between the roller cam and a flat tappet as far as EFI is concerned is nil in my opinion when comparing the factory cams.