Fuel Sender Voltage Question

[twigg]

This is the cover of the manual I am looking at. I have a PDF version of it.

 

The section with the fuel sender is shown a few posts above. Is what your looking at laid out the same as this one?

 

It is a little grainy, but I do not see a connection to ground on the sender.

 

There is already a ground running into the CMU on the 10 pin connector. Wouldn't think they would run two in.

 

Gary

 

Gary I was saying that the wiring diagram shows that the return wire runs to ground.

 

That's meaningless in terms of the physical layout of the wires, it could be grounded at any point along it's circuit, including, as is most likely, inside the CMU.

 

My guess is that if I open the CMU again I will find that the direct path between those two pins will be broken somewhere. That would be the obvious way to ground that circuit, and it would satisfy the bean counters

 

The Manual I have pre-dates yours. It is the original from 1985, the '93s hadn't been designed then

 

The Part # is LIT-11616-04-96

[bkuhr]

Gary I was saying that the wiring diagram shows that the return wire runs to ground.

 

That's meaningless in terms of the physical layout of the wires, it could be grounded at any point along it's circuit, including, as is most likely, inside the CMU.

 

My guess is that if I open the CMU again I will find that the direct path between those two pins will be broken somewhere. That would be the obvious way to ground that circuit, and it would satisfy the bean counters

 

I am trying to figure why the bean counters would have run a ground wire all the way back to the CMU when there are lots of opportunities a lot closer to the tank float.

My 83 does not have return back to CMS. What changed?

I am thinking maybe they build it a 'calibration circuit', maybe like a variable resistor in the CMU adjusted for differences in floats, maybe 1-5 ohms built into circuit when float all the way up (0 ohms across float) = all bars light. Just WAG. If this was the case, just running the bypass wire as discussed would throw calibration off, all all bars would stay lit until float reached ~6-10 ohms, which could be nearly 1/4 tank before gauge started dropping, and at the empty end, still 1 bar lit when looking for reserve switch on side of road.

 

It may be worth it to crack the CMU again just to trace it out, and take pics for others.

[dingy]

Twigg,

 

Is the attached wiring diagram the one you are looking at?

 

If it is, this one does not depict the upgraded CMU, and is very different than what you have in your bike, circuit wise.

 

Also, I hope you know I am only trying to help you here and not win an argument. I don't want to see you damage your bike due to bad info from me.

 

 

Gary

[twigg]

I am trying to figure why the bean counters would have run a ground wire all the way back to the CMU when there are lots of opportunities a lot closer to the tank float.

My 83 does not have return back to CMS. What changed?

I am thinking maybe they build it a 'calibration circuit', maybe like a variable resistor in the CMU adjusted for differences in floats, maybe 1-5 ohms built into circuit when float all the way up (0 ohms across float) = all bars light. Just WAG. If this was the case, just running the bypass wire as discussed would throw calibration off, all all bars would stay lit until float reached ~6-10 ohms, which could be nearly 1/4 tank before gauge started dropping, and at the empty end, still 1 bar lit when looking for reserve switch on side of road.

 

It may be worth it to crack the CMU again just to trace it out, and take pics for others.

 

I'm thinking about it

 

The wiring diagram shows the circuit very clearly. The return wire does indeed run back to the CMU, and it is grounded. As I said before, it doesn't matter where it is grounded.

 

I don't know why they did it. Might it be something to do with the gauge responding with a delay to smooth out the sloshing around?

[dingy]

It may be worth it to crack the CMU again just to trace it out, and take pics for others.

 

You gotta know I got pictures, CMU pictures I got. These are from an 88.

 

Some of these show the jumpers I put in to bypass the warning lights for the headlights.

 

Gary

[twigg]

Okay .... Take a look - very bottom left.

 

http://i1092.photobucket.com/albums/i418/twigg2324/1986%20Yamaha%20Venture%20Royale/IMG_0546.jpg

 

As you can see ... The G/W wire comes from the CMU, passes through the Sender and returns to the CMU via the Black wire. That Black wire is grounded, probably inside the CMU.

 

My gauge doesn't work as it stands, but there is continuity right along the black wire. When I ground that wire it works normally ... so I figure the ground inside the CMU is broken. The harness has no disconnected grounds so it can't be grounded anywhere BUT in the CMU.

[dingy]

OK, I don't get a beer for this one. What your looking at is for the upgraded cluster as I can see the gear selector switch on it.

 

Here is the same cut (almost) from the 86-93 manual. It is in the Electrical/Signal section.

 

http://i1007.photobucket.com/albums/af193/gdingy101/signalwiring.jpg

 

I would personally favor the main circuit diagram myself. Yamaha is known for having numerous errors throughout this manual. And since they did invest in redrawing the main circuit diagram, I would bet on that one. This one looks so close to the 83-85 that I would think they just reused it and it slipped through quality checks. I have seen other instances of them doing that, parts fiche being one.

 

Gary

[bkuhr]

You gotta know I got pictures, CMU pictures I got. These are from an 88.

 

Some of these show the jumpers I put in to bypass the warning lights for the headlights.

 

Gary

RC2 in pic 7 looks promising as a special purpose resistor, maybe adjustment screw on right side I cant see?

[twigg]

Okay ... I bit the bullet:

 

First pic is the back of the board showing the pin mountings. They all look just peachy, but the path to ground isn't happening so I guess there is a broken track or poor solder under the connector on the other side.

 

http://i1092.photobucket.com/albums/i418/twigg2324/1986%20Yamaha%20Venture%20Royale/IMG_0548.jpg

 

Rather than mess around trying to remove the connectors and fix it, I did this:

 

http://i1092.photobucket.com/albums/i418/twigg2324/1986%20Yamaha%20Venture%20Royale/IMG_0550.jpg

 

And guess what ... My Fuel Gauge now works, as does everything else on that CMU.

 

God my wife married a genius :rotf: