Fuel Gauge Bounces All Over

[sfovc2003]

My fuel gauge was not reading accurately (I ran out of gas when it showed almost a half a tank and the red warning light never went on). I had the sending unit replaced and now the needle bounces around so much that I have no idea how much gas I have. Any suggestions on what the problem may be?

[Chsmadden]

Is it wired properly? If not, then flop the two plugs on top. If that doesn't fix this, then you might have gotten a dud sender unit. You didn't mention what year car you have, but this worked on my '74.

[sfovc2003]

Thanks. I'll try that. Mine is also a 74.

[1750GT]

I read a post from Papajam that if you have a Veglia gauge, you'll need a Veglia sending unit and the Jaeger gauge requires the Jaeger sending unit. Does your SU and gauge match?

[Chsmadden]

I think all '74 cars in the US came with Jaeger gauge clusters.

[Alfajay]

Yes, you do need to pair Jaeger sending units with Jaeger gauges, and visa versa. And yes, you do need to get the right wires on the right connectors - can't put the low fuel wire on the gauge connector.

BUT, a bouncing needle indicates an intermittant connecton, not one of the above problems. I'd pull the sending unit out of the tank, and manipulate the float while watching the gauge. Don't forget to ground the sending unit with a jumper while doing this.

Possible causes of an intermittant connection would include

- The wiper isn't making a steady contact with the coil inside that little half moon shaped housing on the sender. If the gauge needle really bounces while you wiggle the float, it points to this symptom. Bend the little brass contact strip to tighten its contact with the coil.

- The sender doesn't have a good ground - try running a wire from the body sheetmetal to one of the sender hold-down screws

- One of the connectors on the gauge or sender is loose, or God forbid, a wire is frayed/broken in the harness

Also, are you sure you have a good bulb in the "low fuel" indicator? Try grounding that wire at the sender to test the bulb, AND that you have the right wire connected to the right sender terminal.

[JoeCab]

The other possibility is that the sending unit is clocked in the wrong position. It can be rotated to many positions. Some positions leave the float/arm more or less sensitive to front/back or side to side sloshing in the tank.

Try rotating it 90 degrees and see if the problem gets better or worse. You may have to try a few before you get a good setting.

[hjauert]

I seem to have the same problem, I have just bought a new sender and the needle in the gauge is now showing the correct reading but when i rev the engine the needle starts to bounce up and down. Does anybody know what to do ?

Regards Henrik

[sfovc2003]

Certainly sounds like the same problem. Just read the posts from the tp and you'll see everyone's, suggestions, all of which are good ones.

[Tifosi]

Somehwere down in the electrical section I seem to recall a thread about fitting a resisitor into the system between the sender and the gauge to aleviate gauge float due to voltage spikes or a 'fast moving' float arm during violent chassis transisions.

I dunno if it would have specific bearing on the problem explained here, but if everthying else turns out to be ok, it might be something worth investigating further.

[BlpltGTV]

I sort of have this issue with mine, but it only registers sloshing fuel. It doesn't bounce unless I can hear the fuel sloshing in the tank. My Empty light has never turned on even when I have run it almost dry. I know the light works as I have grounded the sender to the tank and let the float dangle and gotten the light to kick on, but never when its been installed. It reads more or less correctly, but its just sensitive.

Will

[Chris1750]

Similarly with mine - it waves all over the place as the fuel moves around in the tank. The only time it's reliable is when the tank is either full or empty .....
Other cars have the float enclosed in a perforated cylinder to damp the movement of the fuel in the tank and therefore may give more reliable results.
Any fuel gauge will only be accurate if the resistance change in the sensor is matched to the volume change of fuel in the tank. Odd shaped tanks and variable resistance sensors will result in an approximation of the residual liquid contents of the tank.
If the needle is erratically jumping and the sensor matches the gauge, then this suggests an intermittent electrical fault.
I've never heard of an Alfa with an electrical fault - doesn't happen does it
Chris

[Elmolino]

I have a similar problem, in my '72 GTV. My gauge only works when the tank is full, but it reads at 3/4 and bounces around. A couple of gallons later and it reads nothing. The low fuel light does work though...

[green 69 gtv]

My old one did something like this. It was fine when the tank was full but as I continud to drive the needle would twitch from full to whatever the real gas level was until the tank was empty, when twitching was maximal. I then got a replacement (advertised incorrectly to fit my car) and now, no twitching but the gauge reads backwards (empty when full, full when empty) If I switch the leads on the sender it just reads full all the time with the reserve light on. I've resorted to the tried and true method of watching my odometer--every 200 miles or so means it's time for a fill-up