Rev Limiter/ MEFI 3 computer question
 

I need to know when you "hit the limiter" on a MEFI 3 injected setup, what happens?? Does it cut back fuel, does it pull out spark or ???? I am curious because I burned a piston and I was on the limiter but I didn't see the tach bouncing at all.

My understanding is it cuts out the fuel and you NEVER want to hit the rev limiter on a mefi when running a supercharger. I always have Crockett set rev limiter higher then I'll ever need it then use the msd limiter to actually limit top rpms. I went to mefi 4 for this reason when re-doing my 540 this time,he set rev limiter in mefi at 6400,I chip it at 6200, the OTHER:D Smitty

That's the way I understand it too, Smitty. Just visited a friend of mine that pro-charged his 500EFIs in a 30 ft Eliminator. It's still a bit under-propped so when we went to run it he never let it hit the limiter. I can imagine in a supercharged application how quickly you could reduce quality engine parts to molten aluminum. I don't know why Merc would remove fuel first. Even with a stock motor configuration it just doesn't seem like a good idea to have the throttle plate wide open and then reduce the amount of fuel available.:(

Not only does it cut fuel, but it intentionally misfires. This can cause a fire in the intake if the plug fires when the intake valve is open. I have seen it melt the cupronickel cores in a
Whipple intercooler. They take something like 2000 deg. to melt them. I put a propane torch to one to see what it would do. I think it burns somewhere around 800 deg. and it didn't even leave a mark. The only salvation is that when it burns the core and it melts, the incoming water puts out the fire.:D

That rev limiter has no conscience. It will tear up a perfectly good motor in a heartbeat.
Eddie

You guys are scaring me.
How does the MFEI 1 work on my 1997 502MagMPI?
I hit the limiter quite a few time this past week testing props.
The engine does sound a little like a machine gun when the limiter gets hit.

Then, once the fire is out you hydraulic the motor and trash a good set of rods. Just can't win for losing!:D

That pretty much sums it up:D

In the MEFI 3 and earlier MEFI's the rev limit is a constant that is set, and the parameter actually reads fuel cutoff rpm in the MEFI3.

You can control the spark tables directly and set the rev limit fuel cutoff rpm higher than where you cut the spark down if you want. This may have saved a few motors from the sounds of your experiences.

Bob

This is a perfect example of why GM didn't want everyone to have the software. In the mefi 3 you can set it for spark and fuel cutoff or just spark. It is also important that the resume is not set too close or too far. Too close burns the engine down, too far spits the belts off.

This just proves to me that mefiburn didn't reverse engineer to make their own software, they got ahold of the GM stuff and made their own GUI. Sad, now people get this software and assume they are tuners. :(

Bleh, caught me at a grouchy moment. :p If any of you here are contemplating purchase of the mefiburn software, hold off a little bit. I think it's time for some healthy competition. :)