Elite Marine

You guys without blowers don't really have to worry. Its the forced induction guys that are in real trouble when they go lean

It's not a real tough thing to do to tune an EFI set up providing you have a dyno and O2 Sensor...it's not magic. Building and putting together the right combination of cam, injector and valve train for longevity with HP is more of an art than the tuning.

RichardCranium572

You're right, tuning full throttle on the dyno is fairly simple. It's the transients that are the struggle. Also why GM will have 15 engineers doing transients for ~ 8 months.

thunderusone

You have no idea what you are talking about. Based on what I have read about your combo......you could use some help in both categories....

Elite Marine

I was talking about tuning an EFI engine which I have done many times and I 100% agree with DH572.

My engine was tuned very well by Gary Taylor of TPI. It's the combination of the hull, drive and set up that I am having issues with. And what are the two catagories you reference?

Your solution is???? Enlighten me genius...

Why is that every a$$hole on here has an opinion, yet they never have the actual solution???

MEFIburn

This should be interesting.....

You may want to go back and review what is in a MEFI 3 vs. MEFI 4 regarding rev limits. See the image attached below for a real world example.

You are correct that the rev limit fuel cut-off and resume should be adjusted together. A 100 rpm difference is what I have seen in tunes. This is fairly obvious in the software that these should get adjusted together.

Versus what.... people not having any package to tune their controllers?? You have no idea the huge amount of time and effort it took to decipher these controllers and come up with the MEFIburn package.

Everyone has a rough day sometimes.

... or if you want a package that exists, is supported via phone and email, and run as a part of a professional business, feel free to buy copies for yourself, your friends, your relatives, your dog, etc.

Below is a screen shot logged on a dyno run from a stock MEFI 3 controller hitting the rev limiter. You can clearly see that the BPW of the injectors has been cut to 0 (the previous sample showed 9.60ms of fuel) while full spark is still being delivered, in this case almost 31 degrees at this KPA and rpm level. This engine is under full load on the dyno. I have more logs of both boosted and normally aspirated MEFI 3's hitting the rev limit in this same manner under full load.

Smitty

MEFIburn,

What is your web address and where can I buy the software. I will need to reflash whan I get my motors back together.

thanks,
Smitty

RichardCranium572

I DO have an idea the huge amount of time it takes to decipher these controllers. Your package looks nice and professionally done. Msd's(ingenious) is nice as well.

You might want to look at the 16 bit array at $0x201A,B if you want full control of the rev limiter on the mefi3 There are quite a few other things besides the two rpm bytes at $0x2043,4

JasonSmith

Hey, that is my motor! Really, that is my stuff you see there. Bob has helped Ben "the motorman" & I out sooooooo much fixing what Tyler Crockett had in my MEFI3 as a "tune".

If you guys want custom tuning software, you can get it from many, many places. If you want software & SUPPORT, get with Bob @ http://www.obd2allinone.com/sc/toplevel.asp?cat=32
His stuff works!
Thanks Bob!
Thanks Ben "The motorman" Bowman AKA Tunertech here on OSO.

cobra marty

So are you saying the way to do the rev limiter is, say you want a rev limit at 5500rpm, you make the fuel table go to 6000-6500 rpm and then use the timing to rev limit so at 5500rpm you decrease the timing say 8-10 degrees and more at above 500rpm.

MEFIburn

Thanks Smitty, we are at:
www.mefiburn.com
or the link is also posted above by Jason Smith and Ben Bowman. Smitty, were you or your engine builder able to examine the piston you lost to see what the cause of the failure might have been?

Ben and Jason, thank you for the kind words. Yes that screen shot looks almost identical to yours, but believe it or not was on a MEFI 3 equipped 350 small block rolling on a dynojet, and not your Whipple supercharged 496's screaming along at 95mph!

Excellent call RichardCranium572! The x201A low order bit switch / flag would appear to have the capability of setting the controller to do spark only rev limiting. I do not know how this works in practice because I do not have a good log of it in action, and I do not know the mechanism or algorithm GM might have used to implement it. Some MSD spark setups have soft rev limiting where it depletes spark on a rotating basis so it is gentle on the engine. I will try and set up a test with a MEFI 3 in the next few weeks where I set the rev limits with and without this flag to see the effect on a running engine.

I have gone through the tune library that I have compiled so far, and for the MEFI 3's it appears the factory settings are to use fuel cut off as the mechanism for rev limiting. Most all appeared to be normally aspirated engines. I also had tunes that were boosted applications that were set for spark only rev limiting with that switch / flag set, and some boosted applications that were set for fuel cutoff. There didn't seem to be any consistency in which method was used.

Armed with this information I talked to a number of well known engine builders and tuners who use MEFI's extensively. Again, I didn't get a good consensus on whether one method was better than the other.

Cobra Marty, yes, you can manipulate the tables to do exactly that. Now which is the best method to implement this (or if it is a good idea at all after talking to a few of the builders) I can not tell you because I do not know how the algorithms in the MEFI3 controller make use of this data. By pulling a few degrees out (such as 8-10) or taking the timing all the way down to 0 or -20 degrees, will this cause the engine to backfire and do damage, or will it cause the engine to just laydown and put out no power? Again, I did not get a consensus among the engine builders and tuners I spoke with on this issue.

Ideally the MEFI 3 flag for spark only rev limiting would do some type of soft rev limiting like some of the MSD controllers do where it is gentle on the engine.

I do not have a definitive answer at this point on what is the best way to rev limit on the MEFI 3. I will try and gather some test data on a MEFI 3 in the next few weeks, I have to do a MEFI 3 tune in a car, so I will experiment. This will hopefully shed some more light on the subject.

Maybe Dustin Whipple or someone else with a lot of experience in this area can chime in....