liquidlounge

iTrader: (1)

Am about to finish a long dormant n/a engine project and am wondering if I should just upgrade to the MEFI 4 computer and harness. I like the idea that the ecm and harness are 12 years newer than what I have and the price is certainly reasonable enough. I am planning to only rev the motor to 5400 max, but it seems I read that the MEFI1 doesn't have much in the way of good tuning above 5200 rpms, is this a concern? I am planning on dyno tuning the motor once its buttoned up. Cam is pretty mild. I think I've pretty much concluded that the MEFI setups are still a decent way to go for a basic n/a marine motor; am I on the right track here? Thanks in Advance.

Trash

IF you are going to stay N/A I would keep the MEFI 1 for the following reasons: 1) If you are doing your own tuning its the simplest to learn on 2) you don't have to worry about getting the new wiring harness all hooked up correctly and 3) you have minimized variable changes from when the previous motor/ecm combo ran. If you were to go to a MEFI4 and had problems getting things running it would be challenging to find out if it was a motor issue or a MEFI4 load, wiring or setup issue.

Your new motor should start and run on the stock tune well enough after the engine mods to get base timing set. After that you can start tweaking the fuel tables. Even extensive mods such as larger displacement, bigger cam and heads will be handled adequately by the stock tune for initial start up.

You must have wide band O2 to get your AFR readings and thus make fuel adjustments.

The MEFI 1 loads FAST. MEFI 3 the slowest. MEFI4 is quick to load but not as fast as a MEFI1.

Having said all that MEFI 1 has its weak points.

1) It lacks fidelity in the tuning range. In other words the break points between rpm /MAP are somewhat large. For instance you get your BPW set perfectly for 2800 rpm and 60 kPa and 3200 and 80 kPa but the motor is off slightly (lean or rich) at 3000 rpm. Well 3000 rpm is not a cell point on the fuel table so you have to tweak the four corners around that rpm / MAP as the controller appears to do linear interpolation when between cell points.

This isn't a deal breaker but it does require a little understanding and patience.

2) As you alluded to the max tabled rpm is 5200 rpm. Not the end of the world but you can't tailor the fuel curve beyond that. Myself and several others have run the motors well beyond 5200 rpm (with rev limiter lifted accordingly) and AFRs have remained stable and within limits. Personally I've seen 5600 rpm and can run the AFR up or down by tweaking the last break point (5200 rpm and 100 kPa). Some guys have gone to 6000 rpm with no issue. Often the volumetric efficiency starts taking a dive at the upper rpm range to you may actually need less fuel. Each motor is different. Revving your motor to 5400 is a non-event for even a MEFI 1 ECM. Just raise the rev limiter.

I would start with the MEFI 1 and after you get things running and you really feel the itch for more tuning options dive into a MEFI 4.

I've been running the same MEFI 1 for 18 years and dozens if not hundreds of loads put into it. Works great for a simple N/A application.

Assuming you have the same TB, IAC, MAP sensor, throttle linkage, sensors etc, you will only have about 3 tables you need to play with. RPM/MAP/BPW or fuel table, Ignition ADV/RPM/MAP table and perhaps the ECT BPW modifier.

If you plan on converting to a blown application, then a MEFI 4 is a must. MEFI 1 has no provision for boost.

I wish you luck. Let us know how it goes.

liquidlounge

iTrader: (1)

Trash- Thanks so much for such a comprehensive reply. I don't have the MEFI software and am going to let the mefitune guy out of Wichita a shot at tuning the motor in on a dyno when this project is all wrapped up. I was a little concerned about the age of the ecm/harness and thought with the engine out, I could upgrade to the m4 very easily and for a reasonable cost. Its seem like someone is always looking for a replacement ecm, so I suppose they can deteriorate somewhat with age...and from what I've read, the MEFI 4 should be available for along time. Thanks Again Trash!

Trash

I wouldn't worry so much about the age of the ECM or harness unless it has been soaked in water or is severely dry-rotted. But like you said it's easier to do with the motor out and everything dismantled. In my case I had a working MEFI 1 on hand I knew was a working reliable product and couldn't justify spending the money on another controller and harness. It has worked very well and I'm happy with the results.

If you go with the MEFI 4 you will definitely have a more capable system with room for growth (i.e. boost).

I believe you are in good hands with the guy from Wichita (TunerTech if I'm not mistaken). Working the tune on a dyno can be fun and hopefully you'll see good results.

I look forward to seeing / hearing about your progress.

Best of luck.

JerrodGlover

For those that are thinking some Boost will be in there future and need MEFI3 or 4 how much of a pain is it to change the harness in the boat? Is it worth it to source a used harness or get and aftermarket one?

articfriends

iTrader: (1)

Mint used harnesess are almost impossible to find for 3's and 4's, just buy a new one unless you have a deal fall in your lap, Smitty

Young Performance

Its depends on the boat, but it shouldn't be a problem to swap out the harness in the boat.
Eddie

Pismo10

Great thread.

tunertech

for what it's worth

MEFI 4B can tune on the fly. At some point you do have to stop and flash.

Your MEFI wiring harness can re re-pinned to support any flavor MEFI 3 or 4 and you can do it right in the boat