mefi1, mefi3, mefi4 -Teach Me, Lesson
 

So what is the difference between these ECU's? What did they come on? What years were they used? Which is best to reprogram for 540CID and heads and cam? Which is best for supercharging?

Does anyone have a source for the mates for the efi harness-a connector end like on the ECU box?

Why can't we get a program so we can reprogram the computer?

Re: mefi1, mefi3, mefi4 -Teach Me, Lesson
 

I found this:
http://www.paceparts.com/index.asp?P...D&ProdID=84483

Re: mefi1, mefi3, mefi4 -Teach Me, Lesson
 

What do you think about changing out the mefi computer to a programmable ECU like Accel DFI or Holly? Which wuold you recommend? Could you take a stock 500EFI harness and put the correct plug on it to plug into the new ECu or could you make an adapter/jumper harness to conect the stock harness to the DFI or other computer?

Re: mefi1, mefi3, mefi4 -Teach Me, Lesson
 

Do you have a bad ECU I can take apart for the connectors?

Re: mefi1, mefi3, mefi4 -Teach Me, Lesson
 

What are the connectors used for the MEFI3 and 4 ECUs? Do they have a name? How many pin? Where can I buy them- the male and female connectors?
Are they Delphi micro-pack connector? 24 or 32 or 36 pin?

Re: mefi1, mefi3, mefi4 -Teach Me, Lesson
 

I found that they are 32 pins.

Re: mefi1, mefi3, mefi4 -Teach Me, Lesson
 

ttt

Re: mefi1, mefi3, mefi4 -Teach Me, Lesson
 

Do the MEFI systems have the ability to work within different load ranges at one RPM as do the aftermarket offerings. Meaning, does the ECU have the ability to set different fuel and timing requirements at different load points within one rpm range. (example: 3500 cruise (80-85 kPa/36 deg) and 3500 acceleration under full boost (~140-150 kPa/28 deg)). I feel these are keys to optimum fuel economy and performance.
Can you program timing assistance for in and out of gear idle control to be used in conjunction with the IAC?

I've programmed a few different ECUs (FAST, Holley Commander, etc...) but never have had the opportunity to play with a MEFI system.
Just curious..
Thanks,
Dave

Re: mefi1, mefi3, mefi4 -Teach Me, Lesson
 

Yes, the mefi software allows you to change the fuel and timing maps according to different loads at the same rpm. Yes, you can put the timing wherever you want it, again, based on different loads and rpm. It is for the most part infinately variable. It will do whatever you want it to do as long as you are smart enough to know.

Re: mefi1, mefi3, mefi4 -Teach Me, Lesson
 

800xcr,
Is that true for the MEFI 2 ECU as well or only the later models? Specifically "Can you program timing assistance for in and out of gear idle control to be used in conjunction with the IAC?"

Rick

Re: mefi1, mefi3, mefi4 -Teach Me, Lesson
 

Yes

Re: mefi1, mefi3, mefi4 -Teach Me, Lesson
 

So what are the differences.
I had heard that Tyler Crockett had said the 1 and 2s did not have these capabilities.
Sounds like these may be a viable option if you could get the software.
Thanks,
Dave

Re: mefi1, mefi3, mefi4 -Teach Me, Lesson
 

I don't think that any of the MEFI 1or2 ECM's make a distinction between being in or out ot gear as far as idle speed control or desired idle speed is concerned.

A few other things to note;

MEFI 3 has Shift interrupt and load anticipation (for inboards) capabilities.

MEFI 4 has Distributorless Ignition, Waste Spark ignition, and Sequential Port Fuel Injection capabilities.

Dave

Re: mefi1, mefi3, mefi4 -Teach Me, Lesson
 

Thanks Dave...great info!!
I don't think there is a distinction either; the ECM just tries to maintain the desired idle RPM with the IAC regardless of in or out of gear. I have found that with some larger cams that the IAC cannot quite keep up or have enough range when dropping into gear to maintain idle. The aftermarket ECMs have a feature to assist the IAC by using timing advance to maintain the idle speed when dropping into gear. Works very nicely.
I was just wondering if the MEFIs have this capability?
Dave

Re: mefi1, mefi3, mefi4 -Teach Me, Lesson
 

When I watched tyler crocket programing my mefi I distinctly remember when the "fuel table #" which i think is your 140-150 kpa at max went above 100 it could no longer measure and correct the injector pulse width even with a 2 bar map sensor so there is one of them educated guesses in the programing up top where he just plugs in what he thinks you probably need. On the dyno my motor(540 cu inch/procharger m3sc/9-10 psi boost,944 hp/962 ft lbs twq) idled strong at 700 rpm's and had a/f ratio's in the 11.2-11.5 range thru out the power band after Tyler spent hours making changes and adjustments. He could take the throttle at idle and stab it and motor would respond great. In the boat was a different story,even after checking all conections,timing,etc boat would idle fine BUT was almost impossible to get from idle to 1200 rpm's. I bored and threaded a o2 sensor port into my manifold and took it back to him for fine tuning on the water.He was able to get motor to come off idle like a stock merc after adjusting several variables on his lap-top hooked to the merc mefi. We also ran boat in 200 rpm increments from minimum planing speed to WFO full boost. There were a couple of small areas where motor was actually lean in the powerband but there were quite alot of areas that were in the 9.8-10.2 A/F ratio. Its surprizing how rich motor ran compared to on the dyno.He went back thru the fuel tables and basically rewrote them in those rpm bands,we'd make another run,check the A/f,make more correction,another run,etc.It took about 5 hours on the water and the boat runs about the best it can.After seeing and doing this I really believe now that the intial tune on the dyno should be just to get you on the water,then a final tune as installed should be made while driving the boat. Imagine a motor running at 9.8 afr that should be closer to 11.8,thats 20% too much fuel!!It might sound extreme but if tyler builds a motor for someone or does the tuning on the dyno he is sometimes willing to fly to your area and ride in your boat with his laptop making final adjustments until the thing is close to perfect(of course you would have to pay his airfare and labor),Smitty

Re: mefi1, mefi3, mefi4 -Teach Me, Lesson
 

Smitty,
Your thoughts parallel mine exactly. "On the water" is a different animal which is why I like the lap top and closed loop with logging.
It's much easier for me to go back and review a few hard runs and make accurate changes to the program at all levels of operation while sitting at my desk :D You can really see what's going on in real life.
Dave

Re: mefi1, mefi3, mefi4 -Teach Me, Lesson
 

Neither the ecm or engine care if its in or out of gear or idle or WOT....its just a dumb piece of iron that does what it is told. Large cams are no issue, response rates can be modified. The system will do everything you need it to do, if you know how to do it.

I've rarely seen an issue with cruising rpm or higher if its done on the dyno, but like I said, either the dyno operator doesn't understand why and how to load it down low to represent off idle, or the dyno won't hold at that rpm.

If you go to the dyno with a different exhaust or for that matter anything else different than how its installed in the boat, you'll have issues.

No question about it, modified fuel injected engines require the ability to tweaked.

You should only use a 3 or 4 for supercharged applications because of their ability to recognize boost. 1' s and 2's are fine for non boosted applications.

Re: mefi1, mefi3, mefi4 -Teach Me, Lesson
 

Its much simpler than that. 1 & 2 configurations don't recognize anything other than a 1 bar. You can still use a 1 or a 2, it just takes longer to get there. Plenty of them out there running just fine.

Again, an engine only does what its told to do, its not its fault if the parameters or setup isn't right.

Re: mefi1, mefi3, mefi4 -Teach Me, Lesson
 

Sorry Dave, but the mefi2 can be programmed for shift interrupt or load anticipation as well as boost control. The mefi4 CANNOT do sequential fuel control. Wasted spark can be turned off in the mefi4 but will be wasted spark on crank. The mefi5 can do sequential fuel control. ;)

Re: mefi1, mefi3, mefi4 -Teach Me, Lesson
 

How many drivers in Mefi5?

Re: mefi1, mefi3, mefi4 -Teach Me, Lesson
 

Good question JC, I'll look into that, but if I remember correctly it only has 8 coil and 8 injector drivers.

Re: mefi1, mefi3, mefi4 -Teach Me, Lesson
 

I think so too.Not positive

Re: mefi1, mefi3, mefi4 -Teach Me, Lesson
 

Sorry, I can't help with the Mefi 5. Haven't had my hands on one yet.