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Tachometer reads high after running battery low

JohnnyRay

JohnnyRay

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I was refueling a few weeks ago, and had the key in the ignition to watch the fuel gauge. Well, I completely forgot about it for a week and the battery was completely drained when I got back to it. I switched to both batteries and the boat started right up. Unfortunately, the tachometer was no longer reading properly - reading high and occasionally wavering up and down by several hundred RPM. We took the boat for an extended cruise to charge the battery and the tach seemed to settle down to normal readings after some time. Fast forward to yesterday's cruise and we seem to have the same problem. I switched batteries with no improvement. Ideas?

BTW - The boat is a 2019 SSXAPGP with an F150XB
 
JR, my suggestion would be to contact your dealer as this sounds like a warranty issue. However, we do have some quite knowledgeable folks on this board, so perhaps one of them will actually have some suggestions you can perform on your own.
 
JohnnyRay said:
I was refueling a few weeks ago, and had the key in the ignition to watch the fuel gauge. Well, I completely forgot about it for a week and the battery was completely drained when I got back to it. I switched to both batteries and the boat started right up. Unfortunately, the tachometer was no longer reading properly - reading high and occasionally wavering up and down by several hundred RPM. We took the boat for an extended cruise to charge the battery and the tach seemed to settle down to normal readings after some time. Fast forward to yesterday's cruise and we seem to have the same problem. I switched batteries with no improvement. Ideas?

BTW - The boat is a 2019 SSXAPGP with an F150XB
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Have the battery tested, it's probably unsalvageable since it completely discharged. I bad the same thing occur to my battery and it would never charge completely, had it tested and it was junk.
 
In response to all of the comments and suggestions -

Both batteries showed a static voltage of 12.6-12.7V at last check, so the drained battery apparently took a full charge. CTEK 4.3A charger/maintainers were then applied to both batteries for several days with the same results on both - fully charged. The batteries are the original fitment from Bennington. Continental lead-acid type.

I ran down battery #1 originally. I recharged it with the outboard's alternator - first with the switch set on battery #1+#2 and thought I saw the tach readings settle down to "normal". The next outing, I switched back to #1 only and saw more erroneous readings. Shut the boat off and switched to #2 only (the presumed "good" battery) and continued to see high and varying tach readings.

I currently have the battery selector set to "all off" now. That will ensure that all electronic systems will restart at zero voltage on the next outing.

I did get the Bennington 10 year warranty transferred to me when the boat was purchased in 2021, so next step will be with the dealer. That brings me to a question though - where is the hour meter data stored/accumulated? In the gauge assembly or in the Yamaha ECU?
 
JohnnyRay said:
In response to all of the comments and suggestions -

Both batteries showed a static voltage of 12.6-12.7V at last check, so the drained battery apparently took a full charge. CTEK 4.3A charger/maintainers were then applied to both batteries for several days with the same results on both - fully charged. The batteries are the original fitment from Bennington. Continental lead-acid type.

I ran down battery #1 originally. I recharged it with the outboard's alternator - first with the switch set on battery #1+#2 and thought I saw the tach readings settle down to "normal". The next outing, I switched back to #1 only and saw more erroneous readings. Shut the boat off and switched to #2 only (the presumed "good" battery) and continued to see high and varying tach readings.

I currently have the battery selector set to "all off" now. That will ensure that all electronic systems will restart at zero voltage on the next outing.

I did get the Bennington 10 year warranty transferred to me when the boat was purchased in 2021, so next step will be with the dealer. That brings me to a question though - where is the hour meter data stored/accumulated? In the gauge assembly or in the Yamaha ECU?
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A "load tester" at your local auto store checks the battery for load conditions, not its voltage. AutoZone or Advance don't charge for that test. I'm sure the Bennington dealer can load test it, too.
 
lawaustin said:
A "load tester" at your local auto store checks the battery for load conditions, not its voltage. AutoZone or Advance don't charge for that test. I'm sure the Bennington dealer can load test it, too.
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True. But starting/CCAs are not the issue, so that would not be a helpful test. The starter spins quickly on the drained battery now that it is recharged. If I had a bad cell, then I could have weak cranking and low operating voltage - but I don't. The alternator is working and charging/supplying continuous operating voltage.

Still had the wonky tach operation on our last cruise though. It may well be a coincidental failure and not related to the previously drained battery...don't know that yet. I was hoping that someone else had seen this and could say how it was resolved.
 
This may be a stupid question but where are you getting all of your readings? Is it through a Simrad or Yamaha GPS? I am wondering if it's calibrated correctly. I am having problems with my Simrad. Doesn't seem to be calibrated correctly. (I have a 55 gal gas tank and my Simrad said I had 10 gal remaining. I went to fill up and it took 54 gal at the dock. smh...)!

Hope someone can help you. You probably need to go to a Bennington dealer.
 
Julianna said:
This may be a stupid question but where are you getting all of your readings? Is it through a Simrad or Yamaha GPS? I am wondering if it's calibrated correctly. I am having problems with my Simrad. Doesn't seem to be calibrated correctly. (I have a 55 gal gas tank and my Simrad said I had 10 gal remaining. I went to fill up and it took 54 gal at the dock. smh...)!

Hope someone can help you. You probably need to go to a Bennington dealer.
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No stupid questions! My readings are digital voltmeter readings at the battery switch terminals. My only displays are the tachometer/hour meter, fuel gauge and trim gauge. The tach used to read what appeared to be accurate and stable readings. What I see now is readings of (apparently) up to 1000 RPMs too high
 
Strongly suggest giving it to the dealer just to keep it in warranty. I’d be willing to bet a bad connection somewhere is to blame, usually a ground wire. Please let us know.
 
Potential bad connection - check all connections to the tach gauge, ignition switch and grounds (check your electrical distribution block and battery cables). Could be a bad tach - if you have a way to swap in a new or borrowed one, that should be a quick check. Could be something in the charging/rectifier on your outboard. I'd let a mechanic check that.

Engine hours are stored in the outboard ECM. You can either get a gauge that displays this or have the dealer hook their Yamaha laptop to it and give you a report.
 
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Ditto turning these over to a dealer to take a look at. In case something has went bad prematurely, it’s still under warranty and can get taken care of that way potentially.
 
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