Reserve Fuel switching

[Chickenlegs]

Can anyone tell me where to find the electric switching tap/solenoid that changes the fuel supplies? My bike only runs on reserve and chokes up on the main tank. I suspect its a slide solenoid and maybe has some crap in it to stop it sliding right across. Just probably needs a clean but cannot find it.

 

[02GF74]

no, not like that.

from manual:

 

[Chickenlegs]

Its not the sensor. Its the reserve tap mechanism that is electrically operated that I need to find. Thanks anyway. Anyone else got a clue on this?

 

[redneksoldier]

There is no mechanism. Actually, there is no physical reserve either. The sensor senses low fuel, the light comes on and the pump stops. Flip the switch to reserve, it bypasses the sensor, and the pump comes back on. Follow the troubleshooting posted above and you will find the problem.

 

[02GF74]

Its not the sensor. Its the reserve tap mechanism that is electrically operated that I need to find. Thanks anyway. Anyone else got a clue on this?

Who told you or where did you read this?

On gen 1, the reserve tank operation is described in the manual I posted above - there is no reserve tap, manually or electrically operated - it's basically a reminder; when low on fuel, the light comes on and then soon engine cuts out so that the rider has to operate the reserve switch, to positively enforce them to think about getting fuel.

Please take a look at the wiring diagram for your model and point out the item you are looking for.

 

[Chickenlegs]

Thanks guys. I was unaware of this method of reserve fuel. I though that it must be a switching system but I understand now that its done with sensors and cutting the fuel. I must have a dodgey sensor. Its actually a pretty advanced system for a bike of that age. Thanks again. I was "over-thinking" the problem. Will check that sensor reading under the RH side panel.

 

[Chickenlegs]

Does anyone know what the OHM reading should be and also illustration 3.6?

 

[02GF74]

Photo shows 1.2 k ohm; spec is 700 to 1100 (1.1 k) ohms.


Re 3.6 it looks like the connector for the level sensor sits next to the rear brake master cylinder, possibly hiding behind the right hand side panel.

 

[Chickenlegs]

Thanks for that. I'll be onto it today hopefully.

 

[one2dmax]

If the bulb in the dash is out the system will not work. The bulb will illuminate during engine cranking (along with the low oil bulb). If the wire is broken in the sensor (which can be seen when looking into the neck of the tank) it will not work. The sensor in the tank must be exposed to air AND have power applied. When the key is first turned on you will take 5-10 minutes for the sensor to heat up enough to turn on the light (which will glow dimly at first then brighter as it heats up). If you swap the gauge cluster out and don't keep the original wire cluster the pump and warning lights will not work.

The RES position (to the left) is a force on position. This will force the pump on regardless of fuel remaining, regardless of bulb condition, regardless of sensor condition, and regardless of this cluster is installed.

The pump runs through various safety systems and will only come on for about 5 seconds if the bike is also not running and sending a tach signal to the fuel pump relay. If the On/Kill button has corrosion on the contacts it will not allow power flow properly though the various circuits preventing not only the pump from work but other stuff like the vboost. If you can hear the vboost cycle when you turn the pump on then the On portion is good and making contact.

This system is ingenious because before this you would have had to manually turn a reserve lever (which is what the Venture had) which would have been too far down on the bike to safely do while riding. BUT, later yamaha's were smarter and made the low fuel light stay on anytime the pump position switch was in the RES position. That way if you forgot to move it back to ON then it would keep the light lit even if you had a full tank. If you don't do that with the Vmax and run out again then the low fuel light isn't going to save you a walk.

 

[Fire-medic]

I'm glad Sean reposted this info, I've been waiting to see it, as he's made the posts before. It's probably something that should be a sticky if it isn't already, specifically referencing the fuel delivery system, the reserve function, and the switchpod.

Actually, it is: (58) The V-max fuel reserve (guage) explained. | Yamaha Star V-Max VMAX Motorcycle Discussion Forum (vmaxforum.net)

Here's the copy, you can see at the link, the attachment pics. The font I see at the link is tiny, I copied it and it's much-easier to read, here:

The V-max fuel gauge explained OR How and why it works and why it sometimes doesn’t.

Many V-max riders are puzzled by the workings of the V-max fuel warning light.

This Q&A is designed to answer some common questions and provide a technical explanation of how the system works and why it sometimes doesn’t work.

Q: “How big is the V-max fuel tank?”
A: The V-max fuel tank capacity is 15 litres, 3.3 Imperial gallons or 4.0 U.S. Gallons.

Q: “How big is my reserve tank?
A: The V-max does not have a reserve tank. The V-max has one fuel tank equipped with a low fuel level sensor and a low fuel warning light. The warning light will glow briefly when the ignition is turned on and turn off if the fuel level is higher in the tank than the low fuel sensor. If the fuel light stays on, the fuel level is below the level of the low fuel sensor.

Q: “If there is no reserve tank, why does the V-max have a ‘RES’ switch on the right hand side handlebar switch assembly next to the throttle grip?”
A: When the fuel level is low and the low fuel warning light is glowing continuously the fuel pump relay disables the fuel pump. In order to get at the fuel that is left in the tank the rider must move the switch to ‘RES’. This re-activates the fuel pump and you are on your way again.

Q: “Why does Yamaha turn off the fuel pump when the low fuel warning light comes on and then make you turn it back on again by using the reserve switch?”
A: This lets you know that it’s time to fill up. The V-max fuel tank is underneath the riders seat and is not a gravity fed system. Fuel has to be pumped up to the carbs so using a fuel cock to switch to the reserve supply is not an option. It’s a sure fire way to get your attention and not overlook the fact that your low fuel warning light is on. The fuel is pumped from underneath the seat so switching to reserve has to involve the fuel pump.

Q: “How much fuel is in the reserve fuel supply?”
A: On a new bike the reserve is approximately 3 to 4 litres but there will be individual variation between bikes. On an older bike the reserve may be considerably less or virtually nothing. Because of the way the sender unit works, the low fuel warning light can mean “As Good As Empty”.

Q: “How does the low fuel warning light work?”
A: The low fuel level sensor unit in the V-max fuel tank is a solid-state thermistor device. That means it has NO moving parts, N0 float and NO contact switch. Many other brands of bike use this type of sensor.

A thermistor is a semi-conducting material that allows current to flow when it is warm i.e. does not resist the flow of electrical current when it is warm but will resist the flow of electrical current when it is cool. A thermistor is best thought of as a slow switch.

The sensor uses the fuel in the tank as a heat sink. When the fuel level is over the sensor it is cooled by the fuel, becomes less conductive and prevents the input voltage from completing an efficient circuit to the electrical ground connection. This keeps the warning light off.

When the fuel level is below the sensor the surrounding air is not an efficient heat sink so the thermistor warms up and allows current to flow. This turns the warning light on.

So when the resistance in the circuit is high the fuel in the tank is above the low fuel level and when resistance in the circuit is low the fuel in the tank is below the low fuel level.

The resistance value for an unsubmerged fuel level sensor is 900 ohms +/- 200 ohms @ 20 degrees Celsius or 68 degrees Fahrenheit.
Q: “Why do some people seem to be able to go much further on their reserve supply and others just barely make it to the next fuel pump?”
A: The fuel level sensor is a temperature and voltage dependent resistor.

Variations in temperature, the quality of the electrical connections and the power available to the circuit will all affect its ability to complete a circuit to the warning light.

Here are some examples.

Example One – Temperature effects resistance.

It’s summer and your motor is hot, your aftermarket pipes have done away with the heat shield between the tank and the rear headers. This has warmed the fuel in the tank and so it is no longer an efficient heat sink for the thermistor in the fuel level sensor. Warm fuel will allow electrical current to flow through the circuit more readily than cold fuel so the low fuel warning light may come on early. In this case you would have (relatively) more fuel in the reserve supply. However, when a cold, wintery, wind chill is cooling the tank the low fuel light might come on at a relatively lower fuel level.

The low fuel warning light on the V-max will vary with temperature of the fuel heat sink.

Example Two – Corrosion increases resistance.

Corroded electrical connections (power and ground wires) add more resistance to the warning light circuit and make it difficult to complete an efficient electrical circuit. Your V-max will see this high resistance as a full tank. If the connection is severely corroded, the fuel sensor may never detect a low fuel reading.

Example Three – Fuel pump relay failure
A faulty relay may not be obvious. A faulty relay can have various types of fault each with it’s own consequences.

Here are a four relay faults and their consequences.

1) The green wire from the fuel pump relay powers the low fuel level sensor. If the voltage drops on this line, the thermistor will be way out of spec and may not activate the low fuel warning at all. The relay may still switch the fuel pump on and off and make all the satisfactory clicking noises when you power up the ignition and flip the ‘RES’ switch and still fail to deliver the required voltage to the fuel sensor.

2) If the relay is faulty and no voltage is supplied to the fuel pump when the fuel level is high but it will supply voltage to the pump when the fuel level is low, you are going to have to ride with the ‘RES’ switch flipped on all the time.

3) If the reverse is true then you can use the upper fuel level but you won’t be able to access the reserve fuel supply at all.

4) A total failure means the fuel pump won’t run. In either the ‘RES’ or ‘ON position.

Example Four – Changing OEM globes and instrumentation

[FONT=&quot]You fit a ‘replacement’ globe to the low fuel warning lamp. Non-standard bulbs may change the electrical load on the thermistor circuit and cause false readings. Replacement bulbs must be rated the same as the original. Ditto replacement instrumentation.

Illustrations
1. Thermistor Sensor removed from can
2. Thermistor can (a Panasonic component)
3. Fuel level gauge
4. Fuel lamp 'off' circuit
5. Fuel lamp 'on' circuit
6. Thermistor data sheet

I hope you find this useful. As usual, comments and input are welcome.
[end]

Courtesy of member gleno

Note that mention is made of ways the relay can fail affecting the fuel pump operation and also the importance of Sean's observation about the bulb being the correct wattage, and functional and the importance of the wire harness for the faux tank gauges for the fuel level, and that low-fuel lamp.

 

[bobbydwatkins]

I'm glad Sean reposted this info, I've been waiting to see it, as he's made the posts before. It's probably something that should be a sticky if it isn't already, specifically referencing the fuel delivery system, the reserve function, and the switchpod.

Actually, it is: (58) The V-max fuel reserve (guage) explained. | Yamaha Star V-Max VMAX Motorcycle Discussion Forum (vmaxforum.net)

Here's the copy, you can see at the link, the attachment pics. The font I see at the link is tiny, I copied it and it's much-easier to read, here:

The V-max fuel gauge explained OR How and why it works and why it sometimes doesn’t.

Many V-max riders are puzzled by the workings of the V-max fuel warning light.

This Q&A is designed to answer some common questions and provide a technical explanation of how the system works and why it sometimes doesn’t work.

Q: “How big is the V-max fuel tank?”
A: The V-max fuel tank capacity is 15 litres, 3.3 Imperial gallons or 4.0 U.S. Gallons.

Q: “How big is my reserve tank?
A: The V-max does not have a reserve tank. The V-max has one fuel tank equipped with a low fuel level sensor and a low fuel warning light. The warning light will glow briefly when the ignition is turned on and turn off if the fuel level is higher in the tank than the low fuel sensor. If the fuel light stays on, the fuel level is below the level of the low fuel sensor.

Q: “If there is no reserve tank, why does the V-max have a ‘RES’ switch on the right hand side handlebar switch assembly next to the throttle grip?”
A: When the fuel level is low and the low fuel warning light is glowing continuously the fuel pump relay disables the fuel pump. In order to get at the fuel that is left in the tank the rider must move the switch to ‘RES’. This re-activates the fuel pump and you are on your way again.

Q: “Why does Yamaha turn off the fuel pump when the low fuel warning light comes on and then make you turn it back on again by using the reserve switch?”
A: This lets you know that it’s time to fill up. The V-max fuel tank is underneath the riders seat and is not a gravity fed system. Fuel has to be pumped up to the carbs so using a fuel cock to switch to the reserve supply is not an option. It’s a sure fire way to get your attention and not overlook the fact that your low fuel warning light is on. The fuel is pumped from underneath the seat so switching to reserve has to involve the fuel pump.

Q: “How much fuel is in the reserve fuel supply?”
A: On a new bike the reserve is approximately 3 to 4 litres but there will be individual variation between bikes. On an older bike the reserve may be considerably less or virtually nothing. Because of the way the sender unit works, the low fuel warning light can mean “As Good As Empty”.

Q: “How does the low fuel warning light work?”
A: The low fuel level sensor unit in the V-max fuel tank is a solid-state thermistor device. That means it has NO moving parts, N0 float and NO contact switch. Many other brands of bike use this type of sensor.

A thermistor is a semi-conducting material that allows current to flow when it is warm i.e. does not resist the flow of electrical current when it is warm but will resist the flow of electrical current when it is cool. A thermistor is best thought of as a slow switch.

The sensor uses the fuel in the tank as a heat sink. When the fuel level is over the sensor it is cooled by the fuel, becomes less conductive and prevents the input voltage from completing an efficient circuit to the electrical ground connection. This keeps the warning light off.

When the fuel level is below the sensor the surrounding air is not an efficient heat sink so the thermistor warms up and allows current to flow. This turns the warning light on.

So when the resistance in the circuit is high the fuel in the tank is above the low fuel level and when resistance in the circuit is low the fuel in the tank is below the low fuel level.

The resistance value for an unsubmerged fuel level sensor is 900 ohms +/- 200 ohms @ 20 degrees Celsius or 68 degrees Fahrenheit.
Q: “Why do some people seem to be able to go much further on their reserve supply and others just barely make it to the next fuel pump?”
A: The fuel level sensor is a temperature and voltage dependent resistor.

Variations in temperature, the quality of the electrical connections and the power available to the circuit will all affect its ability to complete a circuit to the warning light.

Here are some examples.

Example One – Temperature effects resistance.

It’s summer and your motor is hot, your aftermarket pipes have done away with the heat shield between the tank and the rear headers. This has warmed the fuel in the tank and so it is no longer an efficient heat sink for the thermistor in the fuel level sensor. Warm fuel will allow electrical current to flow through the circuit more readily than cold fuel so the low fuel warning light may come on early. In this case you would have (relatively) more fuel in the reserve supply. However, when a cold, wintery, wind chill is cooling the tank the low fuel light might come on at a relatively lower fuel level.

The low fuel warning light on the V-max will vary with temperature of the fuel heat sink.

Example Two – Corrosion increases resistance.

Corroded electrical connections (power and ground wires) add more resistance to the warning light circuit and make it difficult to complete an efficient electrical circuit. Your V-max will see this high resistance as a full tank. If the connection is severely corroded, the fuel sensor may never detect a low fuel reading.

Example Three – Fuel pump relay failure
A faulty relay may not be obvious. A faulty relay can have various types of fault each with it’s own consequences.

Here are a four relay faults and their consequences.

1) The green wire from the fuel pump relay powers the low fuel level sensor. If the voltage drops on this line, the thermistor will be way out of spec and may not activate the low fuel warning at all. The relay may still switch the fuel pump on and off and make all the satisfactory clicking noises when you power up the ignition and flip the ‘RES’ switch and still fail to deliver the required voltage to the fuel sensor.

2) If the relay is faulty and no voltage is supplied to the fuel pump when the fuel level is high but it will supply voltage to the pump when the fuel level is low, you are going to have to ride with the ‘RES’ switch flipped on all the time.

3) If the reverse is true then you can use the upper fuel level but you won’t be able to access the reserve fuel supply at all.

4) A total failure means the fuel pump won’t run. In either the ‘RES’ or ‘ON position.

Example Four – Changing OEM globes and instrumentation

[FONT=&quot]You fit a ‘replacement’ globe to the low fuel warning lamp. Non-standard bulbs may change the electrical load on the thermistor circuit and cause false readings. Replacement bulbs must be rated the same as the original. Ditto replacement instrumentation.

Illustrations
1. Thermistor Sensor removed from can
2. Thermistor can (a Panasonic component)
3. Fuel level gauge
4. Fuel lamp 'off' circuit
5. Fuel lamp 'on' circuit
6. Thermistor data sheet

I hope you find this useful. As usual, comments and input are welcome.
[end]

Courtesy of member gleno

Note that mention is made of ways the relay can fail affecting the fuel pump operation and also the importance of Sean's observation about the bulb being the correct wattage, and functional and the importance of the wire harness for the faux tank gauges for the fuel level, and that low-fuel lamp.

 

[bobbydwatkins]

What an awesome job explaining the reserve switch. I especially found your information regarding the fuel pump relay as a potential problem very interesting. I have a 2003 Vmax that starts running out of fuel after about 85 miles with no warning light illuminating. I was thinking it was possibly the sensor in the fuel tank but you have to remove the swing arm and everything just to gain access. I think what I may be experiencing is 3rd relay fault you mentioned above. So do you think by simply replacing the fuel pump relay it will solve my problem as it is much more accessible.
Thanks Bobby Watkins

 

[MaxMidnight]

What an awesome job explaining the reserve switch. I especially found your information regarding the fuel pump relay as a potential problem very interesting. I have a 2003 Vmax that starts running out of fuel after about 85 miles with no warning light illuminating. I was thinking it was possibly the sensor in the fuel tank but you have to remove the swing arm and everything just to gain access. I think what I may be experiencing is 3rd relay fault you mentioned above. So do you think by simply replacing the fuel pump relay it will solve my problem as it is much more accessible.
Thanks Bobby Watkins

First rule of diagnosis: Don't take what others may think is the problem and blindly follow their advice until YOU have confirmed by testing that it is their suggestion that's causing the fault.

Going on to 'reserve' at around 85 miles is, depending how you ride, normal. Does the bike run when reserve is selected then if so it is performing as intended.
If the reserve light does not come on then (stating the bleedin' obvious) the first step would be to check the bulb and that you are getting power to it.

You could also go through the checks in the Service manual (7-52).

 

[Zeus36]

As MaxMidnight said, check the bulb first. My 1997 was running out of fuel at 75 miles on the odometer with no low fuel light, but I would see the light illuminate during start up. It ended up being a broken solder joint on the fuel sensor (see the arrow in the picture). The sensor assembly can be removed from the bike without pulling the tank or swingarm. I re-soldered the connection and it's been working as designed since 2015.

 

[bobbydwatkins]

As MaxMidnight said, check the bulb first. My 1997 was running out of fuel at 75 miles on the odometer with no low fuel light, but I would see the light illuminate during start up. It ended up being a broken solder joint on the fuel sensor (see the arrow in the picture). The sensor assembly can be removed from the bike without pulling the tank or swingarm. I re-soldered the connection and it's been working as designed since 2015.

View attachment 91563

 

[bobbydwatkins]

The bulb was the first thing I checked and it is good. I just get to approximately 85 miles (depending on how aggressively I've been riding) and switching to the reserve position has no effect. It's like I have no access to the remaining fuel. The only test I did not perform was the fuel level sensor as it didn't state in the manual if the tank needed to be full or not. And wouldn't that make a difference in the ohms reading? Further from reading above it sounds like the "thermistor" part of the sensor can be very sensitive and I live in Arizona where it's very hot.
I appreciate your guys help as I did not know you could remove the sensor without removing the swing arm. (the manual said it needed to be removed when replacing) I will test the sensor and solder joint before moving on to the fuel pump relay.
Thanks again!
Bobby

 

[brian hicks]

What an awesome job explaining the reserve switch. I especially found your information regarding the fuel pump relay as a potential problem very interesting. I have a 2003 Vmax that starts running out of fuel after about 85 miles with no warning light illuminating. I was thinking it was possibly the sensor in the fuel tank but you have to remove the swing arm and everything just to gain access. I think what I may be experiencing is 3rd relay fault you mentioned above. So do you think by simply replacing the fuel pump relay it will solve my problem as it is much more accessible.
Thanks Bobby Watkins

I always set my odometer to 0 when I fill up. I find my red light comes on at about 93 miles and I switch over to res. Mine is then good for about 20 miles. My red light has been dim lately and it's easy to miss when the sun is shining but when the bike starts to stall then a quick flick of the switch fixes it.

 

[telelinkken]

I got no light anytime, at about 60mi sputter-sputter switch to "reserve" and quickly get to gas! ???

 

[Fire-medic]

Like brian hicks, I get ~93 miles to hit reserve, and it's just over 1 gallon left, from past fill-up experience.

"...at about 60mi sputter-sputter switch to "reserve" and quickly get to gas!" Sounds like someone running triple digits across an empty of population state, or a region empty of people. Watch-out for large-sized wildlife! I was speaking with a friend who lives in SW MI and she told me about having hit a deer with her bought-new Mercury Marquis, and less than a month later, her husband hit another deer. She said after the second impact, their insurance agent told them, "now when I see your number on the phone for an incoming call, I wonder if the deer population claimed another vehicle!"