Hello OSO!
This engine seems to have a couple of problems...
If i rev it over 3000 or 3200rpm, i get a soft alarm. All gauges okay. if i go back under 3000, the soft alarm stays. until i shut off the engine.
A soft alarm should be under 3000 and become a hard alarm above 3000 am i right?
What could cause a soft alarm to go off above 3000 and keeps staying until shut off?

could this be a DTC alarm?

2001 502 MEFI3


Thank you!

You will have to scan it for codes other wise your just guessing and replacing random sensors. If you dont have a scanner I know you can make one with LED light and paper clip. To clear it you move throttle from 0-100-0% If i remember correctly. You will have to google it.

There is only a hand full of codes on MEFI3. These systems are about as basic as it gets at least In the past i had a code 44, knock sensor. Would only get a beep at higher rpms. I just had to unplug the knock sensor wire, electrical cleaner spray, and put a little dielectric grease on it and plugged back in.

EDIT: If you need to make code reader
https://teamtalk.mastercraft.com/fil...tch?id=2747433

Okay, so you think it could be a dtc? I have scannerpro, i try reading it, or i take the paperclip method. I hope it saves the codes, because if i restart the engine the beep is gone. Or is it possible if i get the beep to just let it run and set the paperclip?
in scannerpro the code reading looks kind of difficult to me.

Not positive on yours BUT I had a customer with twin 305s in a 38 foot cruiser with mefi4 that had a alarm AND reduced power above 3000 rpms for oil pressure safety alarm switch, NOT the sending unit that actuates the gauge. so that switch is normally closed , pressure to open. His failed closed and oil pressure would NOT open it which set of his alarm and reduced power. It was the first time i saw that send a engine to reduced power, I think on a 502 mag it sets off the alarm but does NOT reduce power. you could simply unplug the oil pressure safety switch on back of engine, (single wire, switch is small and usually to right of the distributor behind intake). IF alarm goes away, you found issue, Smitty

Your alarm is the equivalent of the check engine light in your car. You don't know anything without pulling the codes.
Make sure you drive bottle has fluid in it above the level sensor; and that all engine sensors connectors are secure and plugged in.
Those are roughly the only/easiest/dumb things you can check.

Anything else is literally throwing parts at the boat hoping one fixes it.

You may find it beneficial to buy a Rinda scanner or DiaCom software for your laptop so you can scan things yourself without waiting to get into a marina/mechanic.

Hey Smitty,
I thought about this at first, but i think a LOW OIL PRESS / HIGH COOLANT TEMP / LOW DRIVE OIL Alarm should give me a soft alarm under 3000 and should get to a hard/steady Alarm above 3000. What I don't understand is why she gives me a soft alarm above 3000 and keeps it until i shut down the engine, if i restart it, the alarm keeps gone until i rev it over 3000 again.

Looks like another kind of Alarm, so i thought maybe its the Alarm for DTC Codes?

Hey Sydwayz,
I will try Scan it for any Codes, i hope it has saved any. If not i have to check for codes on the run.

Test drove her today, reved over 3000, got soft alarm. 1sec on, 3sec off. Above abd under 3000rpm. Didnt stop until I restart the engine. After restart we have no alarm. Scanned for codes pending while driving, she throws knock sensor code.
I heard of knock codes because if engines that just do not knock. I drive on 95 octane fuel.

Knock sensor will some times alarm without detonation doesn't have to be fuel or timing related, check the connection / wiring, replace sensor ? Id also double check the timing.unplug it and retest

Good guess i had on code 44 and knock sensor. Same thing happened to mine. MEFI3 will move the timing around to see knock. If it doesn't see knock. beep beep Code 44.

Could try to unplug it, (Starboard side of the block around the starter)..... clean it, little dab of dielectric grease and plug it back in. Worked for mine. And yes the 502 MPI likes 87 octane.