Faulty engine alarm

My engine alarm goes off for seemingly no reason

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7 Palmas

New Member
Jul 8, 2019
13
Boat Info
DA 270 1997, GMC Sierra, Humminbird
Engines
7.4 mercruiser Bravo 3
My engine alarm goes off for no apparent reason. Mercruiser 97, 7.4l, MPI, Bravo 3.
When cruising my alarm sometimes goes off and rpm cuts out for a few seconds. Temp is normal and I've replaced the alarm sensor twice. What's going on?
 
Steady beep, double start up beep, continuous intermittent beep ?
And...

What alarm sensor did you replace? There are multiple.

Does the RPM only cut-out when the alarm is sounding? What RPM's were you cruisng at and what do the RPM's drop to?

There's only a couple things that would cause a "limp" mode.

7Palmas... do you have a MEFI-2 system? In your model year, you might... which I believe means only a solid horn and even less things that are monitored. Temp, pressure and drive lube, I believe.
 
And...

What alarm sensor did you replace? There are multiple.

Does the RPM only cut-out when the alarm is sounding? What RPM's were you cruisng at and what do the RPM's drop to?

There's only a couple things that would cause a "limp" mode.

7Palmas... do you have a MEFI-2 system? In your model year, you might... which I believe means only a solid horn and even less things that are monitored. Temp, pressure and drive lube, I believe.
Replaced Temp and Lube sencors.
Rpm does cut out usually cruising at higher RPMs only for a few seconds then picks up again sometimes to a higher RPM than I started with. It looks like it drops to 2000RPM.
Yes I believe I have the MEFI-2 system.
My mechanic has done the diagnostic hookup (in the shop) and found no errors. He's is leaning towards disconnecting it.
 
The more info you give the better. Answer some of LD's questions in post 3, and anything else that might help.
 
Change out the oil pressure sender, or short it out while at cruising rpm and see if it causes the rpm to drop as you indicated. That might be the culprit.
 
All 3 of those sensors work on a ground trigger. Try disconnecting them and testing them 1 at a time.
 
Change out the oil pressure sender, or short it out while at cruising rpm and see if it causes the rpm to drop as you indicated. That might be the culprit.
I have shorted out the the oil pressure sender and alarm still goes off.
 
Change out the oil pressure sender, or short it out while at cruising rpm and see if it causes the rpm to drop as you indicated. That might be the culprit.
 
That was the gear oil sender I shorted
 
All 3 of those sensors work on a ground trigger. Try disconnecting them and testing them 1 at a time.
Thankyou I'll let you know how i go but it won't be till spring now. Just to let you know Oil Pressure gauge reads normal and so does Temp Gauge. I've disconnected gear lube container and alarm still goes off.
 
What the gauge reads means nothing, it's what the ecm sees. You now know it isn't the lube bottle.
 
No Oil Pressure and Temp gauges read normal.
 
Had the same thing..turned out to be a failing systems monitor...basically false alarm.
Note my engine is a 1995 7.4 carb, so not quite as modern as yours....
Old school analog gauges are the best monitor you can get, temp, pressure, etc. they do not interpret anything, just show you the facts of what the engine is doing.
I had to disconnect my systems monitor and just watch my gauges, which is what I do anyway.
 
Thanks Keysohana, I will consider doing that. Did your engine revs drop as well?
 
No, the engines ran great with the alarms going off, when I removed the systems monitor board, I found it was bad.
 

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