Testing tachometer signal wire

Ken O · Posted: Tue Apr 13, 2021 2:26 pm Post subject: Testing tachometer signal wire

My tach shows zero RPM. Engine is a Honda BF90A, tach is a 7000 RPM Honda/Faria. The ground at the tach tests good, the positive at the tach tests good, and the engine shows good charging voltages when running. The dial on the back of the tach is set to "1" which should be correct for this engine. The tach didn't work when I bought the boat. How can I test the gray wire to see if the problem is tach, wiring harness, or engine?

thataway · Posted: Tue Apr 13, 2021 4:19 pm Post subject:

Generally the way to test for a signal, is to put your digital volt meter on "AC" and measure the voltage between ground and the wire to the tach. (One may be ground and you can determine this with the continuity testing) The output is pulsed D, but most DVM will not register they rapid pulsed DC--where they can AC. Look for about 3 volts. Don't put the DVM on any other setting than "AC".

From what I can gather from both the Seloc manual on the 90 and my full shop manual on the 135/150 is that the signal comes from the main computer. (ECM) module.

Probably more likely a bad gauge that a bad sender--but you won't know until your test.

Ken O · Posted: Tue Apr 13, 2021 5:44 pm Post subject:

That's just what I need. I'll give it a test this weekend. As usual, thanks a bunch for a speedy and detailed reply.

kcohen4

I repowered with a Yamaha so have no need for the Honda. Also have a tilt gauge
If you want them just pay the postage.

Ken O · Posted: Tue Apr 13, 2021 11:19 pm Post subject:

Thanks for the offer. I'll test both this weekend and let you know. It appears that the tilt gauge moves to the "nose down" setting when powered and stays there no matter what position the engine is in, so I may be in the market for both gauges. My engine is a 1997, so I'll need to check if they are the same units. Is the tach 7000 RPM?

Thanks.

VicC · Posted: Wed Apr 14, 2021 12:53 am Post subject:

On the back of the tach there will be the wire landing posts. I believe "power", "common", & "signal". If your DMM has the feature to measure hertz (Hz), then select this and measure between comm & signal with the motor at idle. If you see a measured value, you can further test this with a little fast idle to see the Hz increase with increased RPMs. If so, then this will tell you that your tach is toast if you don't see the needle move accordingly.

For the motor position, my Honda BF 50s have the tilt sensor located on the left hand side of the motor about mid-transom. This little black sensor has a lever arm against a fixed part of the motor that moves the lever when the motor is trimmed. When nosed down the lever arm is pushed. When nosed up, the lever arm has a spring return. I believe this sensor is nothing more than a little potentiometer. What happens is that this gets gummed or salted up and the spring return cannot overcome the stick.

kcohen4 · Posted: Wed Apr 14, 2021 7:33 am Post subject: Honda Gauges

Yes 7000 RPM
See pictures
http://www.c-brats.com/modules.php?set_albumName=Annie-M&op=modload&name=gallery&file=index&include=view_album.php

Click on my photo album

Ken O · Posted: Wed Apr 14, 2021 11:30 am Post subject:

To kcohen4: I'll take the gauges. I sent you a PM. Thanks!

To Vic: Thanks for the thoughts on the tilt gauge and on the tach. It does sound like the tilt sender is stuck. The boat had not been in the water for 10 years when I bought it. I'll try your fix. If it's the gauge, it sounds like I'll have a spare...

As a new owner, I really appreciate the C-Brats community! Thanks all.

journey on · Posted: Wed Apr 14, 2021 4:30 pm Post subject:

As you know, the tilt sensor is a small arm attached to a pot, on the engine. The arm on Journey On regularly gets stuck with salt and needs to be loosened. I assume that all Honda sensors are the same.

Boris