Gas Gauge acting wierd

[Mrtinajero]

The gas gauge on my bike is acting weird all of the sudden. When I start the bike the gauge goes all the way up even if there is only maybe a quarter tank in it. Then when I'm riding it, it fluctuates between what I would assume to be the correct measurement and being full. Any ideas?

[GLoweVA]

I would suspect that you might have a bad connection somewhere in the circuit.
First try the connector plug at the rear of the tank, just under the seat, near the tank securing bolt.
The manual has a test about the resistance at different fuel levels.

If that's inconclusive, you might try pulling the sending unit out of the tank and making sure that travels up and down smoothly.

While you got the tank off and drained, it might be a good time to pull the petcocks and see how much gunk is on those filter screens.

[3Phase]

Mr. T, how fast does the fuel gauge indicator needle move?

If the needle moves quickly and/or jumps around then the fuel gauge itself is broken. Unfortunately, it can't be repaired.

If the needle moves slowly and smoothly and doesn't jump around then there is a short somewhere in the fuel gauge circuit or the sending unit is bad.


If the gauge itself isn't broken then you will have to check the fuel gauge circuit. Keep a fire extinguisher handy, work carefully, take your time and don't make sparks while the fuel tank is on the bike!

You'll need to find your multimeter, then remove the seat and look underneath the back of the fuel tank. You should see a small 2-pole electrical connector with a Green wire and a Black wire in it.

Set the multimeter to the 100 Ohm range, then unplug the 2-pole connector.

With the ignition switch off measure the resistance on the fuel tank side of the connector.

The sending unit resistance should be:
Full tank - 6 to 10 Ohms
1/2 tank - 28 to 37 Ohms
Empty tank - 75 to 85 Ohms


If the sending unit is good then you will have to check the voltage in the fuel gauge circuit. Keep a fire extinguisher handy, work carefully, take your time and don't make sparks while the fuel tank is on the bike!

Set the multimeter to the 20V DC range, then turn on the ignition switch and measure the voltage on the harness side of the 2-pole connector.

The Green wire should have 7 volts. The Green wire is the supply wire so it should always have 7 volts when the sending unit is disconnected.

The Black wire should have 0 volts. The Black wire is the return wire so it should never have any voltage at all when the sending unit is disconnected.

Slowly turn the handlebars lock-to-lock and make sure the voltage does not change on the Green wire or the Black wire.


If the voltage and resistance tests are okay and there are no voltage changes when you turn the handlebars but the gauge still doesn't work correctly here's what the fuel gauge circuit is doing and you can try to track it down from there:

A 12 Volt Brown wire from the 20 Amp Signal fuse on the fuse block goes up to the tachometer and connects to a 7 Volt regulator inside the tachometer housing that lowers the voltage going through the fuel gauge circuit so there are will not be any sparks inside the fuel tank.

The Green wire runs from the 7 Volt regulator down to a variable resistor in the sending unit in the fuel tank so it should always have 7 Volts on it when the 2-pole connector is disconnected.

After going through the variable resistor the current flow returns through the Black wire back up to the fuel gauge. The current flows to ground through a small coil of precision resistor wire that is wrapped around a calibrated bi-metallic arm attached to the fuel gauge indicator needle.

The change in the amount of current flowing through the precision resistor wire changes the amount of heat applied to the bi-metallic arm that controls the position of the indicator needle.

Again: Keep a fire extinguisher handy, work carefully, take your time and don't make sparks while the fuel tank is on the bike!

[MaximPhil]

Tech Tip

Hey TC, A copy of the above post deserves to be in the Tech tips section.
Phil

[jwhughes3]

agree

Scott you are a font of knowledge! Thanks - filing away for future use.


Hope to get to ride again with you soon.

John

[3Phase]

Thanks, Phil, John!

It's because I've had to fix this stuff so darn many times because it's all getting old and I'm too cheap to buy new parts! I do have a fairly good pile of broken fuel gauges, sending units, tachometers and speedometers to go along with my growing collection of final drives. All I need now is some zircon-encrusted tweezers to put the needles back on and tweak the gauges a little and I'll be stylin'.


Moving to Shizuoka soon,
Gonna be a final drive tycoon.

Movin' to Shizuoka soon

(Yippy-Ay-O-Ty-Ay!)

Movin' to Shizuoka soon....

[GLoweVA]

3Phase, all you need now is: a flux capacitor, 1.21 jigawats and you can go back to the future!

You must have been an electrician in your previous life.

[3Phase]

I was wrong and the description of current flow is backwards!

I am sorry Mr. T but I am a total moron and I had the current flow backwards for the fuel gauge circuit.

It doesn't really change the troubleshooting steps but the explanation is wrong.

I started a new thread with pictures that shows XS1100 Standard Fuel Gauge Component Failures and Adjustments.

[Mrtinajero]

When I start her up. It usually goes up at its regular speed to full and then as I drive it slowly fluctuates. It doesn't jump

[3Phase]

When I start her up. It usually goes up at its regular speed to full and then as I drive it slowly fluctuates. It doesn't jump

This happens when the tank is full and continues until you're about to run out of gas, correct?


The Green wire is shorted to ground or the in-tank sending unit is bad.


Disconnect the 2-pole connector at the fuel tank and turn on the ignition switch.

If the needle on the gauge moves the Green wire is shorted; might be a pinched wire between the tank and the frame.


If the needle on the gauge doesn't move it's most likely a bad sending unit.

[cywelchjr]

If it's the sending unit, I think a unit for a normal standard tank will work in a venturer tank, and I've got a spare one of those sitting in my garage too.

The wires aren't perfect, but are perfectly safe and all and it works fine (or at least it did when I took the tank out of service because of the leaks at the bottom. If that's the problem, it's here if you need it, we just have to pull it out of that junk tank.

[cywelchjr]

I was just thinking. That's how mine acted as my 7v regulator went out. I would go up and down, and then all the way down, and then full scale, and it didn't matter what the gas level was. Then it stopped working at all until I fixed it. I've seen replacements one ebay pretty cheap if you watch around, but you have to spend a little time troubleshooting it to make sure that the voltage regulator is actually the problem.

[3Phase]

I was just thinking. That's how mine acted as my 7v regulator went out.

I'd forgotten about that. That's what mine did too before it went all 12 volt on me and then quit working.

[cywelchjr]

I'd forgotten about that. That's what mine did too before it went all 12 volt on me and then quit working.

See, that's why the collective mind is greater than the sum of the parts. Each of us remembers things that others don't, and we help reinforce each others memory.

[3Phase]

See, that's why the collective mind is greater than the sum of the parts. Each of us remembers things that others don't, and we help reinforce each others memory.

Yeah, I know, thanks for the jog! Hang on a minute... Ace, King, Queen, Jack and Ten of Spades... Uh... Bingo!