2004 Mercruiser 350 Mag MPI Alarms

I have a Monterey 298SC with twin 2004 MErc 350 Mag MPIs serial numbers OM665403 and OM661101.

I have a random double beep can can happen at anytime and sometimes does not happen at all. I have checked all fluid levels, drive, trim, oil; bypassed outdrive fluid sensors, temp sender, sea water pressure sensor, oil pressure sender; and I can't get this annoying double beep to stop. The engines seem to run perfect and my instinct is a bad sensor, but I can't seem to identify the right sensor.

Can anyone point me in the right direction short of buying a computer for it or hiring someone to diagnose it?

Thanks

Re: 2004 Mercruiser 350 Mag MPI Alarms

Sorry, but you will need the error codes read out to determine the source of the problem as a double beep alarm can be caused by a bunch of things.

Re: 2004 Mercruiser 350 Mag MPI Alarms

Re: 2004 Mercruiser 350 Mag MPI Alarms

Zackman said:

I don't think the error codes get triggered by the audible alarm.

I think there are only three things that will give you the trouble alarm. Oil Pressure Switch (not pressure sender), Water Temp Switch (not water temp sender), and the drive fluid level.​

Click to expand...

Zackman, On newer Merc engines, the PCM Engine Guardian system monitors the sensors and the sensor wiring circuits incorporated on the engine. If a malfunction is detected, a fault description is stored in the PCM and the available engine power is normally reduced. An audible alarm condition is also normally created/generated.

The alarms can be a constant tone (for engine coolant temp overheat, low engine oil pressure, engine overspeed, exhaust manifold cooling temp overheat, and sea pump PSI low). A constant beep for low outdrive lube level. Or 2 beeps every 60 seconds.

The 2 beeps every minute can be caused by a bunch of things. Such as a faulty cam, IAC, MAP, MAT, and knock sensors. An electrical open or short circuit in the engine cooling temp circuit, fuel injector wiring circuit, oil PSI circuit, exhaust manifold cooling temp circuit, sea pump circuit or throttle position circuit will also generate a 2 beep/minute alarm. There are other causes as well.

On my 2003 Merc engine, I had an intermittent 2 beep/minute alarm which was stored as a fuel pump relay error, although the engine seemed to run fine. The fuel pump relay was replaced but the problem persisted. When the problem was resolved, it turned out to be a connection in the CAN circuit in the engine wiring harness.

I'd stick with getting the error codes read out to find the source of the alarm. It's too expensive to throw parts at the problem as the number of potential causes is too great. Ignoring the alarm can result in bigger, more expensive problems later.

Look here http://forums.iboats.com/showthread.php?t=251571 at pages 34-36 of manual #36 for more info on causes of the engine alarm on the 350MAG engine.

Re: 2004 Mercruiser 350 Mag MPI Alarms

Thank you all for your replies. The guardian system has not kicked in as I can still run at WOT, however, it still sounds like there are WAY to many things it could be to try to diagnose without a scanner. Wish you could rent scanners ! I hate paying a mechanic for something I know I could fix myself as long as I could identify what it is.

Thanks

Re: 2004 Mercruiser 350 Mag MPI Alarms

Get yourself a Mercruiser Scan Tool or the Rinda Techmate (same exact thing, just different paint job) from http://www.rinda.com/acro/prodlist.pdf

It will do everything the bigger scanners will do, just a smaller screen. so it will take a little longer to find the problem, but it's a lot cheaper than the big boys.

Re: 2004 Mercruiser 350 Mag MPI Alarms

I wanted to add my experience with a similar problem for all to consider.

The boat is a 2003 Maxum 3300 SCR with two Mercruiser 5.0L MPI's with 390 hours.

I had the boat out a week ago and was idling out of the marina when one of the engines quit and wouldn't restart while in neutal/idle position. I could pull the engine out of gear and get it to start at higher rev's (above 800) but as soon as I put it back into neutral the engine would sputter or die with alarm (2 beeps).

When I would start the engine out of gear and run it above 800 rpm, I would get the 2 beep engine alarm every 60 seconds. I would also get the two beep engine alarm (sometimes) when trying to start it with the motor in neutral.

This thread lead me to the conclusion that my IAC (Idle Air Controller) had gone bad and had to be replaced. This was confirmed after I swapped the IAC from my other engine and the motor started perfectly. Boat part = $110, time to diagnose and repair = 6 hours, the trip to the san juan islands afterwards = priceless.

One problem solved. I just went on a 5 day trip and the engines are running great, but I'm now getting a very random double beep alarm when the boat is running at cruise speed (3,300 - 3,800). Alarm is not consistent what so ever, so its either trying to tell me something is going bad or a wiring problem exists.

Probably will have to get a mechanic diagnostics on the damn thing = $$. Problem is likely some stupid sensor again (I already replaced on seapump pressure sensor).

There should be a better way for the average joe to find out what his engines are telling him (or the ability to rent a diagnostic computer)

Mike

Re: 2004 Mercruiser 350 Mag MPI Alarms

[SSSMJA] It might be time to change the impeller housing assy also, If the brass housing get's deep grooves in it it could be getting air bubbles to the water {PSI} sensor and they call that a phantom beeping while on the water. Like Don says the only way to know for sure is to have a scaner and your engine manual on the boat with you at all time as part of your tool kit. Here is a link to rinda scan tools you might want to think about getting one for just under $400.00 I believe also as you upgrade boats over the years you will need to update the tools chip every few years.