what kind of IAT's are you seeing? On the ones I dynoed with extra injectors the BSFCS even with "good" afrs everwhere kinda sucked (mid .650s to low ,700s at wot), that was tuned for 12.0 or so at beginning of boost and into mid 11.5s at top at 8 or 10 lbs of boost

so upgrading to a Mefi4b I can delete the injectors at the throttlebody? I removed the throttlebody today and inside the supercharger I had raw fuel piling up.

my understanding is those injectors helped “cool” The whipple?

I would post some pictures but apparently I don’t have 10 posts yet so I am not able too

A mefi4b wouldn't change whether or not you choose to add fuel at throttle body, it would, however allow you to have a "cleaner" tune overall. In a boat application their are 3 reasons a mefi4b is better than a mefi 3:
Spark/fuel tables end at 6000 rpms in a mefi3 , they go to 9000 on a 4b, so IF you want to build a motor that runs past 6k with a mefi3, you have to put whatever you want from 6000 up in AT 6 k and it is what it is.
Boost multiplier table, a mefi3 can be configured to use a 2 bar map sensor BUT the boost/fuel multiplier table ends at 150 kpa (7.35 lbs of boost) AND is 1 dimensional, ie, if you add 20% fuel at 140 kpa, its adding 20% any time it sees 140 kpa, whether its at 3000,5000 or 6000. A 4b table is RPM vs Boost , it can be set to add 10% at 140 at 3000, 14% at 140 at 4000 etc PLUS it goes to 200 KPA so it can taylor fuel multiplier all the way to 14.7 lbs of boost.
Spark vs boost table is same way
So if you NEED to add different amounts of fuel on a mefi3 under boost at different rpms, you have to do it in the100 kpa box in regular fuel tables. Problem with that is IF your not actually IN boost, that extra fuel you put in is still going to be there. Its npot terrible, Ive tuned some boosted mefi3 stuff that ran fine, just alot easier using a 4 and tailoring the fuel where it wants and needs it. Mefi4 does alot of other things too, but these are the big ones , Smitty

Got it. I might actually upgrade just to be on the safe side and get a better tune for better performance. Let me ask you this, are you still tuning MEFI3? If so what would you say about me mailing it to you(if thats possible) My motor basically has been refreshed and I did go with a roller cam. I had a guy tune it here in Havasu. He is the only person in all of Havasu that has the cable to tune MEFI3 (every shop i called has said the same thing, her is the only one that tunes Mefi 3). He did not build my motor but I had him turn it on the water. I do you have a welded bung And we did run a meter while tuning. Since he has to do it is still running very rich and I told him. Even while tuning at high RPM the boat sputters. It’s to a point where now it is doing it at Low RPM.

I talked to the gentlemen that tuned it and he is telling me to check timing, ignition coil(changed, spark plugs(changed), fuel Pump (brand new Aeromotive), fuel pressure regulator (new). It seems like he doesn’t want to turn it again or fix it. One thing that I do know is when we were on the water he did not check timing. He is making it seem like his Tune was spot on.

Update:

So I take out piggyback and wiring. Looks like the gentleman that built my motor did wire the injectors to bank one and bank two. But he still managed to connect the piggyback and wire it all up. DONT KNOW WHY!!

The gentleman that refreshed my motor and I are not on speaking terms so I did not know or wanted to ask him. It’s a long story!

The piggy back should be separate from the engine injectors..mefi3 or 4 can run 5 high impedance injectors per driver, there are two drives in the mefi3 and mefi4.

so are you saying you are firing the auxillary injectors off your 2 batches AND have the piggy back whipple computer? Are you sure your not looking at the TPS and IAC extensions running from your harness out to your TB?\

I am not using the piggy back at all. My boat never had it. I wired this two injectors in myself, one to each bank.
https://cimg7.ibsrv.net/gimg/www.off...67dd831aa.jpeg

Correct. So what he did was wire (taped into) both Aux injectors to the #5 and #7 injectors. When i took off the plenum i seen the injector connector that comes from the piggyback harness zip tied and Not connected. The TPS and IAC extensions were there but for time reason he tapped into those wires and they were connected to the piggyback harness. It was a complete disaster.

i am trying to post pics but unfortunately it will not let me. I just don’t understand why the piggyback was wired and he tapped into other wires.

With the piggyback being wired and the injector plug not connect (because he tapped into the 2 batches) throw off the MEFI when they were trying to Tune?

That is how mine was wired. Look at my previous response to Articfriends. This guy had a mess in the harness.

in the pic you sent of your fuel lines. The last pic have a read air filter. Is that for your vent hose?