Vans Fuel Guage

ExtraKatana · #1 10-04-2019, 01:49 PM

What is the number one and maybe number two reason a vans fuel gauge will show 0 gallons? Occasionally I can recycle the master and it comes to life. Also, during a turn on the ground I can see the gauge move from the float being jostled. So, it?s not a stuck float.

Ralph Inkster · #2 10-04-2019, 02:34 PM

Have to sometimes run a ground wire from one of the mounting screws to the airframe. Sometimes a bad connection somewhere on the sense wire.

Desert Rat · #3 10-05-2019, 07:08 AM

Most (all?) float type fuel senders are really just variable resistors, with the fuel gauge measuring ohms.

I don't know without playing with one whether a zero gallon reading is zero resistance or infinite resistance, but I'd normally start looking for a loose connection, broken/intermittent wire, or a bad ground at the probe, because if any of that stuff happened, it's going to peg the needle one way or the other. If it's not there, then the next most common would be the probe itself worn out. This is easy to check by putting a multimeter on it, and measuring the ohms resistance. As you move the float up and down, the meter should behave just like a fuel gauge.

HOWEVER- I can't see how any of the stuff I just mentioned could be cured by cycling the master, which you said happened, so if you have old school gauges, I'd just swap them side to side and if the problem moves, then you need a new gauge.

Ralph Ketter · #4 10-05-2019, 07:31 AM

Quote:

Originally Posted by ExtraKatana

What is the number one and maybe number two reason a vans fuel gauge will show 0 gallons? Occasionally I can recycle the master and it comes to life. Also, during a turn on the ground I can see the gauge move from the float being jostled. So, it?s not a stuck float.

I have had this happen when the battery is getting weak. I suspect there is something in the gauge electronics that causes this when the voltage drops too low during engine cranking. I've never had it happen when my battery is good and strong.

reak · #5 10-05-2019, 10:29 AM

I had this exact problem when my plane new and had Vans fuel gauges. I also figured battery and grounding. I fought the fuel gauges for over a year, even replacing them with two new gauges. Finially I took them out and bench tested them. The problem is easily duplicated this way. Power up the fuel gauge normally using a resistor to duplicate the tank sensor(~200 ohms ). This worked every time. Now, reduce the supply voltage below 8 volts and the gauge will latch to 0 gallons every time. After the 0 gallon latch there is nothing that can be done to unlatch the gauge. The only fix is to reduce the supply voltage to 0 and try again. This was repeatable over all fuel gauges.

In my case replacing the battery did not help so I put a latching voltmeter directly on the battery and found even with a new battery the voltage would often drop momentarily to 7 volts during starting.

My conclusion is that the gauges are susceptible to low voltage caused by starting and there is no fix other than to replace the fuel gauge with something else which is what I did. Maybe my Skytec high current starter was the real problem.

Anybody want to buy some Vans?s gauges? I have four.

ExtraKatana · #6 10-08-2019, 07:47 PM

But wouldn't the weak battery be only problematic during starting? I have the problem when the alternator is working too.

Very sporadic. Tried to duplicate the issue over the weekend and couldn't.

If a grounding issue....are the senders ground by the sending unit, meaning I need to remove the tank?

rvbuilder2002 · #7 10-08-2019, 09:46 PM

Quote:

Originally Posted by ExtraKatana

But wouldn't the weak battery be only problematic during starting? I have the problem when the alternator is working too.

Very sporadic. Tried to duplicate the issue over the weekend and couldn't.

If a grounding issue....are the senders ground by the sending unit, meaning I need to remove the tank?

An intermittent sender ground is a common cause for fuel gauges reading zero.

The standard sender has a resistance value of 240 ohms at empty, to 30 ohms at full. So if the ground is open or poor it can cause a resistance that is much higher than the empty tank value of the sender.

The senders ground is via the mechanical connection of the sender flange to the inspection cover, to the fuel tank, and then to the airframe.
The problem is usually between the sender flange and the cover but is occasionally between the cover and the tank.

ExtraKatana · #8 10-09-2019, 06:25 AM

Quote:

Originally Posted by rvbuilder2002

An intermittent sender ground is a common cause for fuel gauges reading zero.

The standard sender has a resistance value of 240 ohms at empty, to 30 ohms at full. So if the ground is open or poor it can cause a resistance that is much higher than the empty tank value of the sender.

The senders ground is via the mechanical connection of the sender flange to the inspection cover, to the fuel tank, and then to the airframe.
The problem is usually between the sender flange and the cover but is occasionally between the cover and the tank.

Very precise answer. thank you!

Brent · #9 10-20-2019, 08:18 AM

Does anyone have experience with Vans flat plate capacitance senders being compatible with the JPI engine monitor. JPI are being very responsive, but not getting any results. I have a Princeton converter for each tank, but still no luck.

If I have to install a float system, has anyone any experience feeding the float wire into the tank with the access plate removed....the wings are on.

One other suggestion was to use the ?Belite? senders, but I am not sure that they would be compatible with the JPI unit.

Any input would be appreciated. Brent