97 speedster twin tach failure

[DeanBrantley]

Newbie here..I just bought a 97 speedster and am learning quite a bit, the hard way of coarse. Just remember to make sure your bimini top screws are tight before you hit WOT lol. So both tachs are out and I started by looking over the schematics on the boat. In them, between the CO-1 and CO-19 cannon plugs it shows a 20k 1/4 watt resistor, one for each tach. I figure that's a great place to start... hook up a meter ect ect. Problem is no matter where I look I cant find the resistors. Anybody know where the sadio/masochist engineers hid these things?

 

[AndyC]

I am working the same problem on a 1995. On the 95, the resistors are located inside of the MPEM box on a little pigtail connector coming off of the rectifier. I've attached a picture that will hopefully help. The resistor is inline inside of the heat shrink tubing, so you can test by hitting the contacts on each end of the gray wire.

If yours turn up bad let me know. I just bought a 10 pack to fix mine and would be glad to share.

 

[DeanBrantley]

Thanks Andy, I'll check it this week and let you know

 

[DeanBrantley]

Found the pigtails, they tested bad. I soldered 2 10k resistors together (didn't have 20k) and soldered into wires.

 

[DeanBrantley]

Tested good Tachs still dont work. I am at a loss here

 

[ialonso]

Tested good Tachs still dont work. I am at a loss here

Any 4 cycle 4 cylinder tach will work if the signal is coming in. It is highly suspect that both tachometers are "bad", but anything can happen . If you are willing to throw parts at it, but the cheapest 4 cycle tach you can find and try with it. Or you can send one of your two to someone that can test it with a working boat.

 

[DeanBrantley]

I'm not quite sure what you mean by "any 4 cycle 4 cylinder tach will work" Why not just use the type of tach for the engine in question? A 2 stroke 2 cylinder. Something I missed here, that's why I think my avatar is so appropriate for my skill level

 

[ialonso]

I'm not quite sure what you mean by "any 4 cycle 4 cylinder tach will work" Why not just use the type of tach for the engine in question? A 2 stroke 2 cylinder. Something I missed here, that's why I think my avatar is so appropriate for my skill level

The engines fire the spark plugs on every half turn, since there is only one coil for both cylinders.You can use the OEM tachometers, but you can also find a tach meant for 4 cylinder 4 cycle engine and it will also count the revolutions the same way.

The logic seems odd, but I have confirmed by trying myself. I have tried 2 after market tachs on the 4 cylinder setting for tachs intended for 4 cycle engines, and it reads correctly.

This is one I tried that did not work for me
http://g01.a.alicdn.com/kf/HTB1wWNg...ometer-Gauge-Car-Motor-Car-Styling-Auto-G.jpg

It also alternates with a voltage display on start and on change. as you speed up, the voltage may increase and you lose the tach function for a minute. Not cool.


This is the one I kept. I know it's foolish to use non-marine parts, I sealed it best I could with good quality silicone. we'll see how long it lasts
http://ecx.images-am@zon.com/images/I/51yZY7cqU3L._SY355_.jpg

 

[DeanBrantley]

Thanks Ialonso, the second tach from amazon you posted, well that link fails. Do you have the manufacturers name? There is one other thing. The resistors were bad so I changed them and still the tachs will not work. Makes me think its something to do with the magnetos but since the mags fire, ie. the engines work, I cant think what that would be.

 

[ialonso]

It is suspect that BOTH tachs would be bad.there must be some way you can test the signal without buying new ones.... I have the 2 that I did not need. If you pay the shipping I can send you mine so you can test. they are sitting in the garage collecting dust.

I do wonder if you can test with a voltmeter on the signal line and see if you get a reading.

 

[DeanBrantley]

Rehashing this with everybody and anybody. Does anyone know how to test for, or what kind of signal one should get from the tachometer wires going to the gauges.

 

[Andy4k6]

not certain on this as I don't have the info here but I would expect a sine wave or a square wave, either way you would need to measure them with on oscilloscope.

Andy