Where Can I check the signal for my tach? - Wrist Twisters
 
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post #1 of 10 Old 03-11-2012, 03:31 PM Thread Starter
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Where Can I check the signal for my tach?

Based on this post:

Link

Still no luck with the tach, can anyone shoot some ideas over? The SM I have printed out is way too unclear to read the wiring diagram in section 20.


Does anyone know where is the tach pickup is so I can check for continuity along the circuit?

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post #2 of 10 Old 03-11-2012, 08:43 PM Thread Starter
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Update : I've followed all SM instructions to no avail. I've got over 12V. To the tach, and continuity to the ecu.

Again, the tach sweeps when the key is turned; however it stays at 0 once the engine is running.
Does anyone have any idea as to how I can resolve this?!?

I didn't factor in a new gauge cluster, wiring harness, and ECU when I settled last fall. Any/all help would be most appreciated.

Cheers,

J

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post #3 of 10 Old 03-11-2012, 09:00 PM
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Sec... let me look.


OK - the tach signal is carried on the Y/G and G/BL wires. These go through the black 9-pin connector in the headlight housing.

The G/BL is the ground. It goes to the vehicle speed sensor under the airbox and to chassis ground.

The Y/G wire is the active signal and goes to the ECM - pin 19 of the 22-pin black connector.

Does the speedometer work?


ETA:
I'm using the Honda shop manual I have for sale in the classifieds section:
For Sale: Honda 919 Service Manual - Wrist Twisters

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post #4 of 10 Old 03-12-2012, 06:46 AM Thread Starter
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Thanks for the response Texas,

The speedometer works well as directed does the odometer. When I test voltages and continuity as per the service manual, everything checks out. Is there a particular wire I can check for a signal to the tach?

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post #5 of 10 Old 03-12-2012, 07:14 AM
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Yes -
The Y/G wire is the active tachometer signal. I'm guessing it is a pulsed 12v signal... not sure if it works on frequency or duration. Frequency would be my guess.

This type of signal is difficult to diagnose with just a multi-meter.

You can have a constant 12v signal provided, though if it does not pulse low at the desired frequency the signal is bad from the ECM.

If you do have a pulsed signal and the tach is not responding, then the tach is bad.

You need a oscilloscope to see the signal; the multi-meter won't display what the signal looks like. The most it will do is give average and/or peak voltage.

Continuity and 12v on the Y/G wire points to an electronic problem, probably in the tach module.

Double check the wiring and the connectors. Look for damage to the wiring harness, too.
If this checks good, then you might want to do a close inspection of the tach module circuit board. Look for loose connections and cold/separated solder joints.

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post #6 of 10 Old 03-12-2012, 10:40 AM Thread Starter
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Before I remove the circuit board from the bike, is there any possibility that the pciii could have failed from the accident? Should I try to remove the tailsection and try just the ecu? Or could using the PC software actually help me diagnose if the ecu is sending the correct signal?

Thanks,

J

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post #7 of 10 Old 03-13-2012, 12:40 PM Thread Starter
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Anyone?

Does anyone think the PCIII could be doing something to the signal?

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post #8 of 10 Old 03-13-2012, 12:44 PM
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i highly doubt it. surest way to find out though is to bypass the pcIII altogether. just unplug it and run straight off the ecu.

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post #9 of 10 Old 03-13-2012, 12:48 PM
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No idea about the PCIII or what it connects to, though removing it would be good troubleshooting methodology.

Yes, I say take it out of the equation and see what happens.

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post #10 of 10 Old 01-11-2013, 05:56 AM
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o.O

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