STB key on Continuous Alarm

[OilBurner]

The Boat has a continuous alarm that starts when you turn the STB key on. I have been chasing this and would like some knowable advice.

This is on a 2005 Maxum 3300 SE. Twin raw water cooled 5.0l MPI mcm engines with bravo 3 outdrives.
Starboard engine is new, which I have installed as a long block. Checked over all the parts removed from the old engine for gross defects and replace those.

Replaced raw water impeller and surfaced the pump impeller plate. The drives were cleaned serviced and inspected at the local shop. New bellows and drive hoses.

The previous owner overheated and seized the engine, and I purchase the boat as is. Port engine runs fine, and no alarms with it.

STB engine starts and runs fine with the exception of the alarm. Analog gauges show normal oil pressure, water temp. I scanned the ECM 555 with a Diacom scanner, oil pressure, water temp, water pressure all are in normal range. No alarms are present with the exception of the alarm stating it is active.

No reduction in power so I do not believe the guardian is kicking in.
There were a few historical codes but nothing significant and nothing came back when the codes were cleared.


I have checked the gear switch. Replaced the water pressure sender. Checked the Ohms on the Drive reservoir and see a change with moving the float.
Disconnecting the drive trim wires made no difference as disconnecting the rear sump. Checked the front sump and shower sump too.

One thing I have not been able to sort out yet is the drive trim gauges are not working. I have not opened the dashboard.

Comparing connections between STB and Port engines everything looks like it’s connected correctly.

I have read many postings and believe checked most of the boxes of typical causes.
Maybe something is back feeding power to the alarm. The alarm is continuous and on engine running or not.

I have a copy of service manual #36 from 2002 ECM 555 and those available on this site.

The boat is currently on a trailer with the drive in a tote of water.

May need to get some professional help with this. Hoping someone might have had a similar problem.

Thanks Oilburner

[shrew]

The alarm should sound when the key is turned to ON, but should stop once the engine is started. I'd look at what is opening the circuit to tell the alarm to stop sounding when the engine is started.

[OilBurner]

Conducted some further inquiries into the alarm issue.

Pulled the dash panel and checked the grounds. Everything came back with good continuity. Could not find anything that seemed to be back feeding power to the alarm. Fixed the issues with the drive trim gauges. It turnout to be something I didn’t get adjusted correctly. I got the new port trim limit switch working and adjusted correctly. But the new starboard switch is not working. It is not giving any continuity. I may need to replace it.

None of these things made any difference to the alarm. With no codes being set on the stb engine, just the constant alarm from key on, I now considered something I feel was a last resort. Just from the standpoint of additional risk of damage to an expensive part. Swapped the port computer to the stb engine and the stb computer on the port engine.

The alarm followed the computer. Stb engine now had normal alarm check at key on and port engine had constant alarm from key on. It was pretty clear the issue was with the computer.

After some online research I contacted Simon Performance Technology and they checked my computer and found a fault in the alarm circuit and replaced the damaged part.

I also asked them to check the idle air control circuit. I had found some evidence that the previous owner had replaced the idle air control motor on one of the engines??? (This owner now keeps a boat maintenance/repair log) I hear this circuit can overheat if the idle air control motor circuit has a fault that causes the stepper motor to constantly be turning on/off searching for the correct setting. The circuit board can’t dump the heat from the added current and it overheats and it smokes the board. (I am just passing along second hand knowledge here and have no direct experience if this is true.) But I asked them to check it out just to be sure.

Simon Performance Technology was good to work with and the turnaround was good. They give a one year warranty.