Tachometer Failure & Charging Voltage

M

MOOSE

Member
My boat has twin 1999 Honda BF40s. Earlier this spring, the port engine tachometer failed, or nearly so, jumping around a bit upon start-up, but then showing no indication of rpm. Thinking the tach was faulty, and not knowing what else to do, I replaced the gauge but there was no change. Then recently, while at cruising speed, I noticed that the port engine was charging at only about 13 volts while the starboard engine was more properly at 14.8. And then yesterday, for whatever reason, the port engine was also putting out 14.8 volts and the tachometer was working fine!

I don’t know how these two circumstances are connected, but they appear to be. And I can even vaguely understand how something in the port engine charging circuitry may have failed such that it was putting out only 13 volts. But what would explain a spontaneous recovery?

All was fine as of yesterday, but I need to understand what is going on for when and if it happens again. Any clue?

Thanks,
Al
 
Ah, unfortunately I don't have a "good" answer for you though I have some information I can at least pass along.

I'm assuming that things have been working well for quite some time and this is a new thing? And your battery switch (or switches) are positioned as they always are?

If so I'd first check for any loose wires, especially around the batteries and switches.

The BF40 has an under the flywheel charging system; that is, there are charging coils under the flywheel that work when a magnet on the flywheel goes by. Some wiring on one of the charge coils could potentially be loose. Also, one of the charge coils could be getting weak (usually due to heat) and/or one of the magnets could be damaged (or loose). Those things are easily checked by removing the flywheel.

Of course the part that's bothersome is that the voltage was low then came back up again. I hate things like that! Unless it happens again with some regularity it means it's not as likely to be the CDI unit (since if it failed it would either stay failed or start to do it fairly often), which would tend to indicate something else in the system is the culprit.

It's a very simple system and most of the components are either simple (like the charge coils) or solid state (like the rectifier and CDI unit); there's just not much to check in the way of other things.

I think you'll likely have to rely on physical inspection of the wiring and a look-see under the flywheel and/or wait for the problem to happen again and try to pinpoint something that triggers it.

Les
 
Les, getting a response from you was more than I could have hoped for; thank you so much.

Yes, everything has been stable for a long time and then suddenly the tach response took a nose-dive. And it was only recently I noticed the engine was not charging properly and only yesterday that I noticed the tach response and charging voltage seemed related.

I've saved your response and will monitor the situation. The spontaneous recovery has me baffled, but my naturally suspicious nature tells me to be on guard for a recurrence. I'll keep you posted and again thank you for helping me sort this out.

Best regards,
Al
 
MOOSE":3sjo9or9 said:
My boat has twin 1999 Honda BF40s. Earlier this spring, the port engine tachometer failed, or nearly so, jumping around a bit upon start-up, but then showing no indication of rpm. Thinking the tach was faulty, and not knowing what else to do, I replaced the gauge but there was no change. Then recently, while at cruising speed, I noticed that the port engine was charging at only about 13 volts while the starboard engine was more properly at 14.8. And then yesterday, for whatever reason, the port engine was also putting out 14.8 volts and the tachometer was working fine!

I don’t know how these two circumstances are connected, but they appear to be. And I can even vaguely understand how something in the port engine charging circuitry may have failed such that it was putting out only 13 volts. But what would explain a spontaneous recovery?

All was fine as of yesterday, but I need to understand what is going on for when and if it happens again. Any clue?

Thanks,
Al
Click to expand...

That is the F/M factor pure & simple. :wink:
 
i hate to harp...But...please just take off your ground cables, polish them up and then WRENCH them down. Your problem and description is absolutely identical to the one I had 2 years ago and innatention caused a costly charging coil replacement. It was intermittent because the cables connections would expand and contract causing irregular resistance.
 
Fairbro":ve2g8zvr said:
i hate to harp...But...please just take off your ground cables, polish them up and then WRENCH them down. Your problem and description is absolutely identical to the one I had 2 years ago and innatention caused a costly charging coil replacement. It was intermittent because the cables connections would expand and contract causing irregular resistance.
Click to expand...

I always wrench my wingnuts down on the battery cables.
 
The reason I was so adament about your problem is because practically every electrical problem I have had on a boat for 40 years has been a bad connection or a non-connection. I once replaced the tilt and trim motor on my Honda only to discover the power lead was sitting UNDER my battery, it got there when I reinstalled the batteries after storage. I don't do that anymore! I hope your problem is gone for good. By the way, you mention you replaced your tack. When I had the same problem I switched the leads to the working tack and same as you, then that one didn't work as well. Anyhoo, Good luck
 
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