No Alphas on 1998 7.4's. All Big Blocks in '98 came with Bravos.

I agree with removing the procharger and selling it. Expect to loose around 7mph off the top speed. You may not even know what top speed is though, since its doesn't run right. You'll need a smaller prop as well.

Thanks again all!
Yes it is the Alpha. I suppose the impeller should be replaced either way, but don't think that is what's causing the water not to pass thru as it worked fine the other night on the water.
I just picked this boat up this last winter so I'm not sure if it cut out last year. The previous owner said no and that it ran 5-10mph faster than I can get it up to. It was an ebay purchase though?
Feel like since I have the charger on it, I need to give it a chance and like the additional power, but running out of ideas and petty cash quick.

Typo...Bravo

Lose the T-stat. Does it cut out while hitting the trim button or all of the time? Check your connections on the fuel pump. Are you running the vacuum activated regulator to increase fuel pressure with boost? If it is runnibg out of fuel as others have suggested you will melt down the pistons for sure. Do you know if the ECM has been reprogramed? It could be detonation and the knock sensor is shutting it down. There is a chance also that the rev limiter is set up incorrectly in the ECM program. As the others say check the simple things first, clean fuel filters, check for flow, etc.
I am also ProCharged and do not run a stat. I make about 100 in running temp with little to no fluctuation. About 80 psi fuel pressure at wot and full boost. You may have a bad impeller with that kind of water fluctuation. The Aeromotive fuel system can put a huge load on your charging system causing the same issue cutting out if you have a weak alternator or battery.
A few things to look for.
Bob
A couple of things to start with.

It seems to be worse when the engine needs to work harder at those rpm (i.e. trimmed down). I'm not sure on the vacuum activated regulator though. Can the ECM be reprogrammed using standard Mercruiser programming or does the charger require something else. My shop is hesitant to work on this on since it's not stock. I'll check the batteries and filters first. Is your exhaust clean coming out of the pipes or do you see steam and maybe some whiter unburned fuel mixture at full throttle

Mine runs a little fat, I get some soot on the transom. It does get some steam at idle. If you are blowing white smoke at WOT I think you smoked a head gasket, that would explain all of it. It could have been caused by an overheat again go back to the impeler on the sea water pump. You should not see a flucuation in temp as you described.
Bob

Maybe I missed it, but are you running a fuel pressure guage? It would be interesting to know what fuel pressures you are running... I just removed a 7.4 mpi with a procharger running a stock ecm that ran very well for the last 100 hours....

I would guess you are using the stock "cool fuel" pump with a piggy back pump... looks like this:



It should have a bypass on the stock fuel pump to replace the stock rugulator (this is usually red also and is tucked way down under on the stock fuel pump) and then you should have an aftermarket boost referenced regualtor (also probably red)

If you check your base pressure, probably 40-45 or so and then see if it begins to climb as you loose vacuum and go into boost, you will know if it is working correctly.

I just put my charger system on a 454mag and had the ecm programmed and it runs like total ****!!! turns out the program is just plain too much fuel and it won't hardly plane out, and just bogs out from over rich condition around 3000 rpm.

You definately don't want to go lean on that engine, but you might be getting to much fuel when the regulator see's boost
and raises the pressure... Does it take a second to "clean up" when you bring the throttle back ?

Another thing is if you are runnig a thermo with no bypass for the ehaust, they will get nice and hot until the stat opens and that could be the steam you are seeing ????

Try this guy @ www.mefituning.com

If the problem is electronical the issue I would agree. If it is a mechanical problem that would nedd to be addressed first.

lilwigs, I don't mean to hurt your feelings but youand your mechanic are obviously in over your head. There are literally hundreds of posts on here to read that will cover all your ???. Either take it to a MARINE mechanic with blower experience or get ready to learn many expensive lessons.
The search feature will answer almost all your ?? because all of us running a procharger have asked or found out the hard way before!

Good luck Brother, hope you get it fixed,Ken.

P.S. I've had a fuel pump work at cruise and fall off at WOT. It good be simple as that. I would recommend taking it off also. You won't regret it.