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Tacho question ...

1438 Views 8 Replies 4 Participants Last post by  Felipe
I have a dead tacho an a bike , not a tL . I understand ( kind of ) How a speedo gets its info from ,a cable or a sensor .
A tacho on the other hand I'm having trouble understanding as there is no pickup .A wire comes from the ecu direct to the tacho .
Where is the ecu reading the revs from ? Can I test if there is some info going to the tacho back meaning the tacho itself is at fault .
Only 2 wires going to tacho ,1 green so an earth the other from ecu .
Electrics confuse me and at the moment I don't know how or what to replace . Its a Honda vfr (rather dull )
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In the case of the TL, and most fuel injected bikes, the rev signal for the tach originates with the crankshaft sensor or the cam sensor. Then it is processed by the ECM and sent to the tach. Is the VFR fuel injected? Even if not, they must use a sensor somewhere. I'm not familiar with Honda's methods.

You wont' be able to measure the active signal going to the tach without a scope (or something similar). A multimeter might indicate that something is happening, but it can't show you the details. The signal will be a pulse train of some sort.
Being 2 wire I would guess its just a simple voltmeter or ammeter, an ammeter is basically a dead short so would show a resistance value of 0-0.5 ohms.
anything higher than that and its probably a voltmeter.

Another type of electric driven tacho is a frequency meter, these need a constant supply voltage, signal and ground (3 wire) and cost more to produce.

Which model vfr is it? or even just what year it was produced
Being 2 wire I would guess its just a simple voltmeter or ammeter, ....
This is what happens when you think things through. Good observation Juzz. :thumbup

Me, on the other hand....:coocoo
Thanks guys .
Ive been doing up this (1991) Tacho is the last thing .
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by the looks of the wiring diagram and the useless test procedure in the manual I would say its a DC ammeter and the ecu outputs a varying current depending on rpm.

I'd start at looking at the signal from the ecm, a voltage ac and a dc test and maybe a freq test. I wouldn't hook it up to an ammeter as if the tacho is a voltmeter than you're shorting out a voltage signal with no current limiter and may overload the ecm or blow a fuse.
My work mate has a very similar tacho so I can test that tomorrow and see what I find
I have power going to the tacho so my guess it got fried when the r\rec, died and cooked it . A common Honda problem apparently on that model .Mine has been replaced so
its possible the fault lies in the tacho itself .
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