Port motor won't get over 3,000 RPM. Out of the hole it climbs to 4K no problem then sputters back to 3k or less.

Batteries are shot, had to charge to get started after boat sat a month. Starboard motor runs fine, one battery is ok but the other is done. Would low juice affect a motor bad enough for it to shut down a fuel pump? Idle is fine and up to 3K it is fine. Merc Guardian system never alerts a problem.

200 hour Mercury 377 cu 6.2 motor- bone stock and very trouble free. Fuel is new tonight (tank was 1/8, filters have less than 5 hours on them)


Any thoughts?

Check your ground cables.Make sure they are tight

Maybe a coil going bad?

We had a 500EFI do that in one of my old boats. We had to jump start that particular engine a few times back to back as the battery would not hold a charge. To make a long story short, the last time we ran it on that battery it started doing what your engine is doing. After checking it out we found nothing wrong with the engine and had no trouble codes showing. Since it needed it anyway and we were tired of jump starting the engine with a battery pack, we installed a new battery and the engine immediately ran fine. So, at least in this case the battery did cause the engine problems.

Do not run computer controlled engines with the batteries all paralleled. There can be no common connection between the electrical systems or the ECu will freak, I had it happen, sounds very similar to your thing. Also make sure your neutral safety switches are working properly-will not run over 3000 in neutral-but light will usually come on when you try.

Ttt

Your ignition, fuel pump, and computer system will be seriously effected if running with a 'shot battery.'

On many newer cars (sidetrack here, just pointing out importance of battery) if the battery is dead the alternator won't charge.

It's not just about voltage - amps are just as important.

If this shot battery is 'soaking up' all of the alternators output, that leaves none for the other components.

Rule #1 with diagnosing mechanical/electrical problems........repair know problem first and then go from there !!!

BTW: Once battery is replaced, as suggested above, make sure ground + pos cables/connections are good and then alternator is working fine.

New batteries put in last night, went out this morning to find identical results to yesterday. Trip to mechanic found no codes, changed plugs, fuel filters(inline and screw on) and motor then wouldn't even run. Lift fuel pump was dead. This is the one that pulls fuel from tank and delivers to high pressure one. At idle/ initial launch it ran ok but when it needed more fuel the motor would choke.

Part will be in Monday, no Land and Sea for me this time.

How bad do you want to go to the run...Get ups red saturday AM early Delivery and install it at the run. Or get Pilot Air freight same day delivery. How far is the part? What time is the run? You can make it.

Call Hideaway and see if they have what you're looking for, 954-943-3200.