454 mpi mercruiser.what is max rpm?
 

i have a mpi 454 mercruiser.(efi component about 96model VST, MEFI1,..brand new 454 long motor, standard)
what controlls max rpm?
EFI box says max rpm 4000-47000.
i'm flat out getting 4000 loaded or not.
is it ecm or something else??
very tempted to go carb.
i want more rpm..more faster.
by the way it is in a jetboat, hamilton 212 unit.
pushing about 2 ton empty and about 3 or 4 with 12 passengers.

Is this a 330 HP?
Merc or GM EFI intake?
When you bought the long block, did you buy with the same cam spec as original?
The EFI may not be calibrated for you new engine.
A carb will be easier to tune for sure...

disagree . if the original 454 w/ similar internals had this efi, then the efi will superior in all respects to a carb once you find the problem... and thats what it will be... a sensor wire left off, the base ingintion timing set incorrectly... something simple.

get a scanner, monitor the realtime readouts and make certain they are in spec, make certain the new motor has a thermostat in it so the water temp gets you out of full rich range and youll be fine, ill bet

If...
If the new engine has the same heads, cam, CR...
If not, then?

Believe me, I like EFI better too, but calibrating it to any old engine is not the easiest thing for us back yard mechanics to do.

I agree with stevesxm. The MEFI computer limits the RPM, but it is set way higher than 4000rpm, probably around 5100.
Water temp is also good advice, because the ecu will hold it in the richened state until the temp is over 130-140 and you will not get any power, plus it will wash down your cylinder walls and then you will have major problems. Give a few more details and maybe we can help more!
Pat is also right in that the ecu has to match the rest of the setup.

In your last thread you said that the engine was missing in the midrange and setting a code 42. Did you get that fixed?

When a code 42 is set the engine is forced to use the ignition modules internal advance curve and you will not get full WOT RPM.

Dave

somebody a few threads ago reminded us that checking that the motor actually sees full throttle after the motor change.......a great suggestion.

thanks guys for the input.
Same engine specs.
Had exactly the same problem on my old engine so asume it's not mechanical.
Never been able to get over 4000..except once a long time ago when i wasn't getting correct water flow through the exhaust manifols and i managed to get 4200 for a short while until i blew an exhaust hose and did a head gasket..
yesterday sent the ecm to a guy to check out. should know the results in an hour or so hopefully..
will keep you updated.
cheers.

Wow this is a good one. How about the sensor that monitors the temperature, not working properly. Heck maybe the ecu is not the right one for the motor. Maybe the ecu is for a 502 and dumping in more fuel than needed. How do the plugs look? Did this ecu ever work properly on a 454 before that you know of?
Here's an idea" do you have any friends with the same setup that you could swap the ecu with. That would verify the ecu is or isn't working.
However, all of this is of no use, if you are under load, because we have no idea what impeller you have installed in the jet, and what power it takes to spin it 5000rpm. If you get this figured out you will absolutely love the EFI setup. Keep working on it and posting here and I think you will find a solution.

This is interesting as I have the exact same problem. I also have a 454 MPI in my 98 Baja 252 and it reaches a WOT RPM of 4000 and no higher. I did get up to 4200 switching from my 21P to a 19P prop but in turn lost top end speed.