Gas Gauge?

First, the gauge needle gets it's ground signal from the sender so check to see that the other side of the fuel needle circuit has 12V going to it, not ground.  

 

Next, check the ground connection at the sender.  One of the mounting screws should not be insulated and should provide ground to the sender.  It may or may not make contact through the tank metal, so check to see if there are two wires going to the sender - the signal wire and another ground (that's what I have) and that the ground wire termination (both ends) is clean and secure.

 

Next, if that doesn't work, check the connection at the gauge - almost all of the terminations on these cars are crimped only, no solder, so make sure it's getting a good connection there, too.  

 

Lastly, see if there is a connector in the circuit somewhere and make sure THAT is secure as well.

 

If all that doesn't cure it, it's either a going-bad sender of a faulty gauge indicator.

Thanks, Gordon it gives me a place to start. From the way it is acting now, just drove it again a couple hours ago and it was doing the same thing. I'm leaning more to an electrical problem rather than a mechanical one.

Gordon: do these gauges have an "exciter" like the VW? I had a bad exciter on the fuel/speedo I bought and it acted like G.R.'s gauge.

I don't think so Ed, just a resistor sender. No exciter, just a boring regular one.

Typically, most folks here aren't running "exciters", although they should help a lot if your gauge needle is swinging wildly.  More accurately, they're called "********s" or "Voltage Stabilizers".

 

Bug city has them;  p/n 113957099AX here>  

 

https://www.bugcity.com/shop/s...0809314C70MhUFF988D0

 

Just wire them in series with your sender wire at the gauge.

 

I have one from my donor....never used.  Maybe I'll try it this Spring and report back.

There is a full "stop" and an empty "stop" at each end of the sender. They are simply turned down tabs that stop the float arm. If the full stop isn't properly set then the needle goes off the end of the rheostat and the gauge jumps back to empty after it reaches full.

The vibrat0r is a voltage regulator for the stock VW thermal fuel gauge. It isn't used for aftermarket fuel gauges nor for the stock VW balance coil fuel gauge. The vibrat0r's purpose is to provide a constant lower voltage to the gauge. It's constant to prevent voltage variations in the system from affecting the reading and it outputs lower than 12V to keep the heating element in the gauge from burning out.

 

Also, when used on the stock thermal gauge, it it connected between +12V and the gauge's power input (plus a ground connection through the case). It is not connected between the sender and the gauge's sender input. If you wired it in series with the sender wire, the vibrat0r, since it opens and closes its bi-metallic contact as it's working, it would actually cause fluctuations in the gauge reading, not smooth them out since it's just constantly disconnecting and reconnecting the sender wire.

 

There is also a need to match the sender type with the gauge type. The float-type sender is undamped against fluid level fluctuations. The tube-type sender itself is damped against fluid level fluctuations because it takes some time for fuel to flow in and out of the small holes. A stock VW thermal-type gauge is damped by itself, it takes some time for the heating element to bend the bi-metallic strip, so it doesn't need the damping in the sender so it will work with either sender type. A VW balance coil type gauge is undamped, it requires the damping provided by the tube sender to prevent needle bouncing.

 

 

All that said, since the current setup was working fine up till now, my bet would be on a loose wire or a broken rheostat in the sender. I would normally expect a bad vibrat0r or gauge to fail completely, not cause fluctuations. And since it was already working, it's not a question of the wrong parts being used together.

And if all else fails, Sierra Madre has a new gauge for $99.95.

http://www.sierramadrecollecti...-Cluster-p19420.html

See, I learn something every day. Especially when Justin speaks. Dude, you have a LOT of stuff in your head! Keep it coming.

One other thing, if you ever do replace a vibrat0r on a stock VW gauge, get the newer black plastic case ones (light bulb and diode internals) not the old thermal metal case type. The old type fails closed and can burn out the gauge, the new type fails open so the gauge just turns off.

Justin - thanks for sharing those GREAT tech tips! I swear I learn something new EVERY TIME I visit this site.