GPS shuttingdown low engine RPM

[britinusa]

The subject says it all, but here's the details.

Garmin GPSMap 741xs, Garmin GMR 18HD Radar, Garmin gWind Wireless Masthead Wind Transducer, Garmin GND 10 Black Box Bridge, Garmin Depth,Speed,Temp Transducer, Garmin NMEA 2000 Network.

When changing from Fwd to Astern (throttle down to idle, pause, shift to other gear, throttle backup) the GPS (not the gWind) will shut down (and it reports that it shut down in the System history)

It seems to happen when the engine goes down to minimum RPM during the gear shift. But it's not easy to reproduce. Normally when making a gear change my mind is focused elsewhere other than on the GPS, so we only notice it after completing the gear change, perhaps not for several seconds/minutes.

My thoughts: Possible Alternator external Regulator is creating the issue. I have a spare and intend to wire it in this week. It's a long shot.

Intermittent faults are the worst to locate.

Paul

[Roc]

Hi Paul,
A fellow dock-mate had a similar issue where his chartplotter got a no signal error from the autopilot.  Turns out it was a loose connection.  Was a sporadic problem where the wires did not make contact, depending on the movement of the wires as the boat moved.  He re-spliced and the problem is gone.  I think this is what I've heard about electronics.  The first thing to check is the connection.  Have you traced all the connections and made sure all is ok.

[britinusa]

Good Point Roc,

that would lead (no pun intended) to a wiring issue that only occurs with very low engine RPM - eg. during periods of high engine vibration!

As the only device to indicate a problem is the GPSMap, that might be a valid point.

I'll clear out the aft berth (garage) and check all the wires down there. The GPSMap has an isolated power line, should be pretty easy to check that wire.

Thanks.

Paul

[KWKloeber]

Paul

Do you have constant voltage when you have the low rippems?

k

[britinusa]

Do you have constant voltage when you have the low rippems?

Hmmm, how to tell? (it's not obvious)

Paul

[KWKloeber]

I guess just hook up a multimeter and watch it as you shift?  More things to have on your mind. 
I'm just wondering if voltage is dropping out and affecting the unit?

k

[britinusa]

Wouldn't the meter just show the battery voltage?

[KWKloeber]

 I'm just thinking for some reason the whole system voltage is going low. A long shot if others are ruled out. Otherwise hook up the multimeter where you can read the GPS voltage?

[britinusa]

I'm just thinking for some reason the whole system voltage is going low. A long shot if others are ruled out. Otherwise hook up the multimeter where you can read the GPS voltage?

I plan to Flash up the GPS and run the engine changing the RPM up and down around idle to see if I can repeatedly replicate the issue (so that I know if I have fixed it later on)

If I can replicate it:
>> then connect the meter to the power cord (it's just below the pedestal guard in the aft berth)
>> replicate it again (just in case attaching the meter also fixed an intermittent power connection problem)
>> If I can still replicate it:
>> >> monitor the voltage and report back.
>> else found the issue. remake the power cord connection
else - screwed 

[KWKloeber]

I'm just thinking for some reason the whole system voltage is going low. A long shot if others are ruled out. Otherwise hook up the multimeter where you can read the GPS voltage?

I plan to Flash up the GPS and run the engine changing the RPM up and down around idle to see if I can repeatedly replicate the issue (so that I know if I have fixed it later on)

If I can replicate it:
>> then connect the meter to the power cord (it's just below the pedestal guard in the aft berth)
>> replicate it again (just in case attaching the meter also fixed an intermittent power connection problem)
>> If I can still replicate it:
>> >> monitor the voltage and report back.
>> else found the issue. remake the power cord connection
else - screwed 

Sounds like a reasonable plan for sure.  Hopefully you find the fail. I HATE problems that magically correct themselves. 

ken

[Ken Juul]

While your checking wires.  Don't forget about the ground.  Trons need a complete circuit, don't just focus on the + side.