Alarm Sounding & Engine Dying???

smcomia · 04-20-2012, 05:11 PM

I have a 97' Z-272 Shabah. Not all of the time but sometimes when I throttle up to get up on plane an alarm will sound and the engine will die. I have asked a few certified merc mechanics about this but have gotten no answers. Has this happened to anyone before??? Everything checks out mechanically and the boat runs great most of the time except for this intermittent issue.

Thanks!

DFZ272 · 04-20-2012, 08:59 PM

First off, in what order is it happening : Is the alarm sounding then the engine quits, or does the engine quit then the alarm comes on like when u first turn on the key, before starting your engine. This makes a difference in what your are trying to figure out. Are you advancing the throttle very rapidly when you are taking off, or advancing the throttle slowly? Try to watch your temp and oil pressure gauges when you take off and see if they do anything funny, like water temp spiking up or oil pressure going to zero. Finding the problem may need more observation/information. It could be a loose electrical connection, bad oil pressure or temp sensor, low oil level in the engine, damaged wire from a sending unit, or even a dirty carb/accellerator pump depending on when the alarm sounds. Try to do some more observation and digging. Sorry I can be more specific, but more info is needed. Hope these thoughts will point you in the right direction. Post back so we can see what you find or if somebody has more suggestions. You may want to send a note to Hudson River Steve on here, he seems to have really good insights.
Happy Boating
Dan

***Hudson River Steve*** · 04-22-2012, 03:20 PM

Is your 454 Mag carburated or injected? Does it shut off cleanly like a switch was turned off or does it sputter a little and then shut off?

smcomia · 04-23-2012, 07:04 PM

Thanks for the info guys! It usually always happens while I am throttling up once pulling out from the dock or from being anchored for a while. I start out slow and gradually give it more throttle to get up on plane and then back off the throttle once up on plane obviously. When the issue occurs it is while I am increasing throttle slowly to get up on plane, that is when the alarm sounds. It is the same alarm sound as when you turn the key on. I have always thought that it is something electrical & maybe something to do with the lanyard switch??? All temps & pressures are good when this happens. When the alarm sounds the boat instantly losses power, sometimes it is intermittent and the boat picks back up and doesn't die and other times it just falls flat on it's face and dies. Rarely but sometimes it also happens just while I am cruising along. This usually occurs when I have been running for a while when we are traveling several miles. Once it dies I just turn the key off, let it sit for a few seconds and then it just starts back up and is fine.

Oh, and Steve it is a 454 mag MPI and it just stalls cleanly without sputtering.

This has left me clueless! Any insight or suggestions would be much appreciated!!!

DFZ272 · 04-23-2012, 08:49 PM

A couple of thoughts come to mind. If the problem is electrical like a loose connection it should be more likely to happen when the boat is getting bounced around. If all the temp/pressure readings are good when this happens it may be something else. I don't have lot of experience with the MPI, but they should have a plug for a scan tool to be plugged in to check the computer for any fault codes. Steve probably has more knowledge on this engine than me. Has the engine been serviced, like has the fuel filter been replaced recently? Has the fuel pressure been checked? I know I am leaning a different direction than before but MPI's are much more sensitive to fuel conditions than carb engines and they have a lot more electrical items to check. I always cut open the old fuel filter when I change one to see if it has a lot of trash in it. Hope this helps
Happy Boating
Dan

***Hudson River Steve*** · 04-24-2012, 12:14 AM

The fact that the alarm goes off and then you lose power sounds like something electrical to me...particularly the low oil pressure and drive oil switches or most likely the engine coolant temp sensor. The low oil pressure and drive oil level sensors will cause alarm to sound but I don't know if they cause the ECM to reduce power. Pretty sure that the engine coolant temp sensor will cause both the alarm to sound and the ECM to reduce the power to the engine.
You can start by disconnecting the low oil pressure switch and the drive oil switches and see if the problem continues. If it doesn't then it is one of those sensors. If it continues to be an issue I would check the coolant temp sensor and its wiring, particularly the yellow wire that goes to J1-2 on the ECM. If for some reason this wire has rubbed through the insulation somewhere and is shorting to a ground, the ECM will interpret this as a high engine temp, sound the alarm and cut power to the engine(Limp mode).

Just to be clear...you hear the alarm first and then you lose power...it's not the other way around...right?

smcomia · 04-24-2012, 02:11 AM

Steve- Yes the alarm sounds then power is lost. I have to apologize because I do not know my way around a boat's electrical very good. So how & where do I disconnect these sensors. Also where is the ECM located?

Scott
1997 Z-272 Shabah

DFZ272 · 04-24-2012, 02:31 AM

Like I said, Steve knows MPI's. The best way to understand the locations and the functions of each wire and sensor is to get a good wiring diagram. The Mercruiser manuals have good diagrams and step by step troubleshooting charts. As I am sure u know there are a lot of wires. I seldom do any electrical work without one.
Happy Boating
Dan