My buddy's 454MPI with longer arms and bigger fists plus .050 lift on a new cam Otherwise bone stock Merc parts.
Stock cal near perfect AFR on the dyno with auto headers
In the boat with SM exhaust it showed a ton of knock retard. Dialed back the advance, added fuel.
Still didn't run right...turned out two injector wires were swapped. How did it run like that on the dyno? Yeah...I don't know either...
Ran like a b-itch finally. spun a 23p 3B right to the factory limiter which was as expected.
Tried a 25p and now it's choking at 4400rpm.

I know, check fuel/water sep, fuel filter, and fuel pressure. Haven't done that yet...out of town travel.

But he's wondering if it's out of injector now that it's seeing a real load. Trying to recall max pulsewidth for injectors around 12.6ms and they might be at/near that right now. Appreciate any thoughts/knowledge.
Happy Easter!

I ran the stock 44lb ones when I had my Whipples. I ran 9lbs of boost with the 44's and had to step up to 60's with 11lbs. 60's were too big to give a reliable idle. I think you'll be just fine with the 44's.
Who did the tune on the ECM?

DIY using MEFIBurn.

That's what we used too. Great tool.

use the .5 rule. for NA application

.5# fuel per estimated HP. i.e. 600 hp / .5 = 300 / 8 = 35# injector at 100% now add the 20 % margin 35*.2=7+35=42# injector.

Just a simple base calc to keep yourself on track. I would use 50's based on this calc

If you want full description go to: http://en.wikipedia.org/wiki/Brake_s...el_consumption

I'm not sure we have enough data to ensure a correct diagnosis. When you say its choking at 4400 rpm do you mean running lean or it just won't pull the RPMs you're looking for?

Chances are when going from the 23 to 25p prop your ECM is tapping into tables on the BPW/MAP table that weren't utilized with the lower pitch prop. The higher load caused by the 25p prop is forcing the motor to attain a higher MAP and the same or lower rpm and you may not have tuned/trimmed the BPW in those tables yet. Those particular values may need to be adjusted.

Are you using a wide band O2 for real time monitoring?

The stock 43 lb injectors are good to about 625-650 hp.

As mentioned, what's going on with the afr's at 4400 rpm? Is it to lean? to rich?

Eddie

As Eddie said if you have 43# injectors that will cover you through the 600 hp mark. I'd guess it's running uber rich with the 25p prop at 4400. But without wideband / AFR info its guess work.

Look at the 3D graph of the BPW/MAP/RPM table and see if you have any weird dips, spikes or holes around the 4400 rpm region.