Fuel Sender Voltage Question

[twigg]

Hey,

 

I am having trouble with the fuel gauge.

 

The sender has been replaced. Currently the tank has done 24 miles since full, and the resistance across the sender is 60 Ohms. So all correct there.

 

The wires from the CMU to the sender both have continuity, and, when connected, the hot (Green/White) side is reading just over 5V.

 

Yesterday I removed the CMU and resoldered a few joints, but mainly it looked to be in very good shape.

 

When I got this bike just about every warning light remained on, and we are now down just to the fuel gauge.

 

Could someone check for me what the voltage should be if when the gauge is displaying correctly, because what I am left with appears to be needing a new CMU.

 

If we have any really, really well informed readers, who know which parts of the CMU control the gas gauge, then I could investigate the precise path in the CMU.

 

There is some small, intermittent fault here as I have, on a couple of occasions, seen the gauge work, or at least try to with the gas pump icon out, and one or two bars on the gauge.

 

Thanks.

[dingy]

Did you check the wire wound board on the fuel sender unit to see if it was bowed.

Sometimes this can be compensated for by adjusting the tension on the wiper arm.

I will try & remember to post a couple of pictures of this adjustment point when I get home.

If you do pull sender back out, don't do with a full tank !!

Gary

[twigg]

Did you check the wire wound board on the fuel sender unit to see if it was bowed.

 

Sometimes this can be compensated for by adjusting the tension on the wiper arm.

 

I will try & remember to post a couple of pictures of this adjustment point when I get home.

 

If you do pull sender back out, don't do with a full tank !!

 

Gary

 

Thanks mate ... The sender is fine. It working right across the range.

 

What I need to know is whether or not the voltage passed through the sender is correct, and which bits of the CMU control this function.

 

I'm perfectly happy to get the soldering iron out again and make sure all those connections are fine before I spring for a new CMU.

[dingy]

Do you have the standard or upgrade CMU?

 

Do you have a gear indicator on CMU is easiest way to explain it.

 

Gary

[dingy]

Do you have the standard or upgrade CMU?

 

Do you have a gear indicator on CMU is easiest way to explain it.

 

Not saying you are not correct about sender, but when it is in tank and gas is sloshing around it could be that the pressure exerted on the float arm is causing the wiper arm to loose a good contact with the wire wound resistor.

 

In the attached picture, there is an arrow pointing to the adjust screw for the wiper arm. If this is loosened and arm is shifted towards resistor a tad, it may make better more consistent contact.

 

Both wires for the fuel gauge come out of the CMU on the upgraded cluster, but I believe the black wire goes to ground, this is what it appears to do on the stsndard cluster without going into CMU.

 

The voltage reading would then be taken from the positive side of the battery to the Green wire with a tracer of varying colors depending on year.

 

The only thing I found in any of the 5 main service manuals I have is a very short description of an ohm meter test for the VMax. It may or may not be similar. The 83-85, 86-93, RSTD and RSV manuals don't say anything about it I spotted. Cut of the page attached.

 

Gary

[twigg]

Gary you are being very helpful

 

If there was an issue with the sender, then the CMU would be showing nearly full right now, because the resistance through that unit is showing 60 Ohms on my meter.

 

As it is, it is showing an empty tank, with the gas pump and the flashing red light.

 

I have a CMU with a gear position indicator. Currently showing "N", as it should.

 

I still don't know what voltage the CMU should be supplying through the Sender.

[bkuhr]

Suggest backstab a ground wire into the wire at the CMS connector that comes from the float, with the CMS hooked up to the bike wiring harness. Zero ohms(good ground wire) should cause gauge to read full. Give it time, on mine it takes 10-20 second/per bar for gauge to increment. (Double check wiring diagram for your bike, that you correctly identify the correct wire at the CMS, and triple check with an ohm check from the unplugged CMS to the wire on the float.)(backstabbing a ground in the wrong pin of the CMS may cause more problems than you want)

 

If this does not work, there is a problem with the CMS.

 

If this does work, do the same ground bypass at the float on the wire contact.-If you did the above ohm check, then gauge should still work.

 

Now assuming it works with ground bypass at the float, but not in normal, this leave just 2 things.

-do the ground bypass to the ground wire side of the float, If this fixes it, repair ground wire problem

-If still does not work, than there is a problem with the float itself.

[dingy]

Gary you are being very helpful

 

I still don't know what voltage the CMU should be supplying through the Sender.

 

That may or may not be a full 12v+. Yamaha may have throttled that voltage feed to the tank sender down to prevent a sparking issue.

 

Gary

[twigg]

That may or may not be a full 12v+. Yamaha may have throttled that voltage feed to the tank sender down to prevent a sparking issue.

 

Gary

 

That's why I was asking. The voltage at the sender is just over 5V.

 

There must be a threshold below which the CMU won't recognise the signal and I wondered if that was the fault.

[bkuhr]

That's why I was asking. The voltage at the sender is just over 5V.

 

There must be a threshold below which the CMU won't recognise the signal and I wondered if that was the fault.

Not 100%, but old CMOS logic that my 83 CMS is based on is 5v for both source and signal referance. I would expect the same-BUT-I would only expect the full 5v with the float UNHOOKED, open circuit. With the float hooked up, I would expect a lesser voltage do to the resistor(in the float) voltage drop, and 0v when tank is empty.

 

This suggest to me, you likely have problem with ground side of float. Do ground side bypass I suggested above

[twigg]

Not 100%, but old CMOS logic that my 83 CMS is based on is 5v for both source and signal referance. I would expect the same-BUT-I would only expect the full 5v with the float UNHOOKED, open circuit. With the float hooked up, I would expect a lesser voltage do to the resistor(in the float) voltage drop, and 0v when tank is empty.

 

This suggest to me, you likely have problem with ground side of float. Do ground side bypass I suggested above

 

The CMU is delivering 5.16V to the sender.

 

Off to try bypassing the ground ... which I thought I did last night but I'll do again and wait longer for a response.

[twigg]

So .... I grounded the return side of the Sender to the battery negative, turned on the ignition and instantly had five bars showing on the gauge.

 

Seems like we have an answer, and I owe someone a beer

[dingy]

So .... I grounded the return side of the Sender to the battery negative, turned on the ignition and instantly had five bars showing on the gauge.

 

Seems like we have an answer, and I owe someone a beer

 

I like beer too. I tried

 

Gary

 

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

[dingy]

Do you have easy access to the back of the CMU on your bike?

 

As I mentioned earlier, on the upgraded CMU, the Black wire was ran back into the CMU, rather than shown as grounded as the standard CMU's are.

 

You might want to check the continuity between the sender and this black wire on the back of CMU.

 

You may still have an issue inside the CMU.

 

I have no idea what just grounding this may do in the long run to the CMU.

 

Here is a link to the 86-87 schematic. Lower left corner is fuel sender.

 

http://www.venturerider.org/wiring/86-87%20Yamaha%20Venture%20DS%20Wiring%20Diagram%20Rev%20D.pdf

 

I may still get a beer out of this yet.

 

Gary

[twigg]

Steve hands Gary a beer.

 

So here is what is happening:

 

If I ground the sender return, then the fuel gauge shows FULL. It should, the tank is full.

 

If I ground the back of the CMU the gauge shows FULL.

 

In both cases, once I remove the ground, the gauge decays, about 10 seconds per bar, to empty and the light comes on. All apparently normal.

 

BUT ... The black wire, from the CMU to the Sender is showing continuity ... and it shouldn't, there should be a break in it.

 

I have two choices here.

 

I can run the sender to a convenient ground, or I can replace the whole wire from the sender to the CMU. Both are easy.

 

Is there likely to be a problem with simply grounding locally the sender return wire? I'm thinking that there should be a problem doing this because the CMU wants a complete circuit, and I don't quite see how it is getting one ... Yet the gauge is working.

 

Maybe it isn't working, maybe it will be stuck on FULL until I fix it correctly.

 

This is an opportunity for a second beer

[twigg]

I had another thought.

 

The wiring diagram shows that wire is grounded, as well as running back to the CMU ... So there could be a disconnected ground on the frame somewhere ... If that's the case then grounding the sender return would explain the continuity AND fix the problem.

[bkuhr]

So .... I grounded the return side of the Sender to the battery negative, turned on the ignition and instantly had five bars showing on the gauge.

 

Seems like we have an answer, and I owe someone a beer

 

Beer not necessary, just glad I could help

My first suspect for the float return ground problem would be the attachment nut on the float itself-corroded,loose,etc. After that likely a connection in the harness you are not likely to find. may have to install permemant bypass

 

Little correction to my above about CMOS logic, I meant to state TTL but was occupied at work.

TTL=5V source and 5V logic

CMOS=5-18Vsource and 5v logic

[bkuhr]

Steve hands Gary a beer.

 

So here is what is happening:

 

If I ground the sender return, then the fuel gauge shows FULL. It should, the tank is full.

 

If I ground the back of the CMU the gauge shows FULL.

 

In both cases, once I remove the ground, the gauge decays, about 10 seconds per bar, to empty and the light comes on. All apparently normal.

 

BUT ... The black wire, from the CMU to the Sender is showing continuity ... and it shouldn't, there should be a break in it.

 

I have two choices here.

 

I can run the sender to a convenient ground, or I can replace the whole wire from the sender to the CMU. Both are easy.

 

Is there likely to be a problem with simply grounding locally the sender return wire? I'm thinking that there should be a problem doing this because the CMU wants a complete circuit, and I don't quite see how it is getting one ... Yet the gauge is working.

 

Maybe it isn't working, maybe it will be stuck on FULL until I fix it correctly.

 

This is an opportunity for a second beer

 

I dont have wiring diagram for 86, and to tired to dig it out from tech library, but if diagram shows sendor return comes ONLY from CMS and not from frame, then the broken ground connection is internal the CMS as a ground OUT, vs other grounds on the CMS as ground IN.

Should not have any problem installing permemant bypass, but I would want it to be 'right', and would open the cms again

[bongobobny]

Instead of reading a voltage, take the sendor unit out and read the resistance from the wiper to ground as you carefully move the float thru it's travel. Youm should see it vary from zero ohms to the maximum resistance value. Chances are you need to add tension to the wiper. As a safety factor, those sensors do not receive voltage, they merely increase the resistance to ground Yes, a small voltage will appear at the wiper contacr....

[twigg]

It's done guys ... fixed.

 

The wiring diagram shows that the return to the CMU is grounded also.

 

When I ground the wire from either end the problems goes away. So somewhere on the frame is an unconnected ground which I shall either find or replace

[dingy]

I just looked at the 'Yamaha' version of the wiring diagram, not the ones one the site here that some rookie drew.

 

The separate ground (Black wire) return to the CMU is the same on the official drawing as it is on the ones posted on this site..

 

My concern is that a manufacturer is not going to run this ground back to the CMU without some other unknown piece of the puzzle coming into play. It doesn't seem like a big cost, but it takes an extra wire in the harness and an extra pin on the CMU & connector to do this. Spread out over 100,000 units sold and this becomes a bean counter issue.

 

I would really suggest if after rechecking the fuel gauge, which I am thinking is OK, that you should open the CMU back up and see if you can trace this circuit in the unit and resolder anything remotely involved.

 

I like Killian's BTW.

 

Gary

 

Area of official wiring diagram referenced.

 

http://i1007.photobucket.com/albums/af193/gdingy101/86-87Yamahawiring.jpg

[twigg]

Gary I have the official service manual with the correct wiring diagram. It definitely shows that the black return from sender wire is also grounded.

 

When I ground this wire the Fuel Gauge works normally.

 

It is possible that the ground is located inside the CMU.

 

I had that open and resoldered everything that looked even remotely suspect. I'm reluctant to do that again because everytime you open those things there is a real risk of something else breaking.

 

My fuel gauge now works, so I'll leave it there but I'll come back here if it quits on me

[bkuhr]

Gary I have the official service manual with the correct wiring diagram. It definitely shows that the black return from sender wire is also grounded.

 

When I ground this wire the Fuel Gauge works normally.

 

It is possible that the ground is located inside the CMU.

 

I had that open and resoldered everything that looked even remotely suspect. I'm reluctant to do that again because everytime you open those things there is a real risk of something else breaking.

 

My fuel gauge now works, so I'll leave it there but I'll come back here if it quits on me

 

Looking at Garys 'official' diagram above, it looks like the main CMU ground IN is the black wire in the bottom pin of the top connector. I would suspect a PCB trace from this pin to the black pin out to the float.

Might suggest trick each segement system into a fault to verify all segements work, and if so call it good.

 

not sure about 86, but my 83 has

 

headlight segement-disconnect bulb

taillight segemant-disconnect bulb

sidestand-actuate stand

eng oil level-temp ground bypass level switch

brake fluid level-open master cover and press on float switch with plastic straw

battery-most with AGM have bypassed. Disconnect (open) bypass wire

fuel level-disconnect green wire from float and apply rheostat or fixed resistors in value from 60 ohm to 0 ohm to ground(or pull float and move arm)

[twigg]

Looking at Garys 'official' diagram above, it looks like the main CMU ground IN is the black wire in the bottom pin of the top connector. I would suspect a PCB trace from this pin to the black pin out to the float.

Might suggest trick each segement system into a fault to verify all segements work, and if so call it good.

 

not sure about 86, but my 83 has

 

headlight segement-disconnect bulb

taillight segemant-disconnect bulb

sidestand-actuate stand

eng oil level-temp ground bypass level switch

brake fluid level-open master cover and press on float switch with plastic straw

battery-most with AGM have bypassed. Disconnect (open) bypass wire

fuel level-disconnect green wire from float and apply rheostat or fixed resistors in value from 60 ohm to 0 ohm to ground(or pull float and move arm)

 

All segments work just fine.

 

I suspect a break in the trace between the Main Ground In and the Fuel Sender Return.

 

Both are black, one is in the top connector and one in the bottom.

 

If I take it apart again I could probably find it, or add one of my own. I'll think about that, it might be a neat solution.

[dingy]

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