If you have any suggestions....

So, I've had a fairly ongoing problem with my boat. It's annoying because its not a big enough problem to keep us from being on the lake, but its annoying driving the boat because it will run rough sometimes. I posted on this last year or year before and still trying to work it out. Heres what its doing...

Starts perfect. Idles perfect. Engage to gear and will putt around perfect. Trying to go from engaged gear to any speed, boat will hesitate and sometimes die. It will do this anytime gas is applied (ie from just entered to gear to 1/4 throttle it will hesitate, maybe die, if it doesn't die it will continue up to speed and run perfect. From 1/4 throttle to 1/2 throttle, it will hesitate and bop bop bop a little, then continue up to speed and run perfect. When I drive, I can almost always keep it running without dying, but the trick is instead of easing up to speed, i go to say 3/4 throttle...it may hesitate a moment, but usually won't die, then start to climb speed at which point I will back it down to desired speed...and it will continue to run perfect!

Symptoms are obvious dying. Quite a bit of black smoke coming when it bogs and dies. Just replaced the IAC and even the new IAC is black so obviously getting too much fuel.

What we are dealing with: 03 Supra Launch SSV Indmar Assault MPI 320 5.7

Steps taken so far: been to 2 different dealers, spent ridiculous amounts of $$ at both and problem still not solved. Supposedly computer reading was sent to Larry at Indmar and by their evaluation the boat should be running perfect. New Cap, Rotor, Plugs, Plug wires. New TPS, New MAP, New IAC. New fuel pump. New fuel filter. Recalibrated Fuel Injectors.

Any other suggestions for solving this issue?

Are you able to PM me the trace that was sent through to Indmar please, not saying I am better than them but have had others in the past where they have missed stuff due to them looking at different parameters and they have picked up stuff I have missed. Also remove the new sparkplugs, keep them in order of the cylinders you pulled them out from and take a picture of the whole 8 together. Have you noticed the symptoms get worse if you have a lot of peeps on board or if you fill the ballast tanks up vs an empty boat and 2 peeps?

By recalibrate the fuel injectors, did they pull them out and run them through a cleaner to make sure they were all flowing the same and one or two of them aren't pulsing intermittently. Or did they just recalibrate the injectors in the ecm. Have you tried running 91 or 93 octane gas in it. If you're running 87 they say you can get by with it, but from experience, marine engines need at least 89+ to run happy. It really sounds like it's a timing or fuel curve problem stemming from the ecm.

@Ian will see if I can track that down, but it was never sent to me. It was in the shop last year so I will see if they still have it recorded. Symptoms occur with just one driver or loaded.

Injectors were removed from the boat and sent away to be recalibrated (if thats the right term), then sent back and reinstalled. Normally running just regular gas, but lately running premium 0 ethanol to see it helps, but no change. Also the shop last year ran it from a separate gas tank and got same problems.

I had one shop recommend getting a new computer, but wasn't sure if that would fix it or not? 1400 for a might fix didn't sound appealing....especially after they they thought it was the fuel pump so installed that for 1100 and it didn't fix it...