Charging system issues
 

I have a twin engine 496 mag ho 34’ Magic Sorcerer, 2001 engines are not Stock 600 HP Raylar Engineering built.
4 New Blue top Optima Batteries
2 New Alternators upgraded to 110 amp for large stereo system.
New AIC both
New MAP sensors both
New Crank position sensors
New Water pressure sensors both and one new pigtail.
Fuel Injectors and Rails removed and cleaned Professionally
New fuel water separators
No pre filter from tank.

Boat Port engine while running WOT will shut off after running only 5-10 minutes.
It will also cough or stumble as well periodically.
Happens even when not running giant stereo.
Periodically after a little running If you trim or Tab it will stumble!
Volt meter while running shows less than 13 volts.

Possibly 5 volt reference issue?
IAC?
Seems to be related to CHARGING SYSTEM.
Sorry serial number sticker on heat exchanger no longer there from age.

First thing Id do is get it scanned or you will be chasing your tail, those engines are so over sensor'd

Fuel pressure good when engine shuts off?

It has been scanned also while running shows available power decrease when this happens. I firmly believe it is electrical/ charging related my thread is intended to have someone mention something that we haven’t thought of yet.

Every post especially back to the BUP days states Scan first, a scanner is money well spent. I get it we have owned an auto repair shop for 42 years. A scan tool gives general direction not here is the problem repair it.

We fixed the water pressure sensors last week because of the 5 volt reference issue.
Showed nothing on the scanner but Port sensor was missing a prong and starboard sensor but connector was damaged also missing grommet to keep dry.
This helped the issue with guardian mode but the scanner didn’t help find it old school diagnostics did.

Great question wasn’t scanning yesterday when it shut down.

Also the batteries are fuel charged individually before running and then when checked after running they are down to 12.2 as of a few minutes ago. No crazy draw from other equipment.

If it is consistently shutting down after a 5-10 minute run, I would consider checking to make sure gas tanks are venting ok. Could also explain the random hiccup

I’ve checked it as much as I can without very invasive helm and floor removal to get to tank. Do you know of a test I could perform short of just listening breather as its filled.

Open your gas fill cap while out running

I’ve thought about that they are connected by the chain and they are heavy stainless billet caps. Maybe wrap cap with rag

Did the problem exist before the new alternators?? Have you verified alternator output voltage and amperage while running???
496 ECM's do not like low voltage at all.
Full charge batteries should be at 12.7v. If they are down to 12.2v after running 5-10 mins

If you are getting a stumble when trimming or tabbing, its taking a power draw from the engines or ground issue

Problem was before Alternators being replaced.
Voltage at idle today was low at stud on back of alternator.
Yes at full charge 12.7
Agree on drawing when using switch but all battery cables including to engine ground are new. Both motors

What is "low"?? Battery voltage? or less than 14? If its in the 13s, your at least getting something from the alternator which means its working, but something is off with the regulator or excitation circuit.. Try revving up to 2000 rpm and recheck the voltage at the alternator post.
Also, do you have a clamp on DC amp meter? would be curious to see amperage output at 2000rpm.
Might also want to check your starter post fuse. I just installed a 105A alternator on my 496, but as part of that had to replace the orange wire in the harness with 4AWG as well as the starter post fuse to 150A from the 90A stock fuse...
You can't just throw a high output alternator on and not change anything.