Repairing your Fuel Sending Unit

Post electrical issues and questions here

Moderators: kamzcab86, CalAltaDubber

Post Reply
User avatar
Briano1234
Whats that smell?
Posts: 4058
Joined: Mon Mar 21, 2005 5:45 am
What year is your cabby?: 1992
Do you own a Cabriolet?: No
Location: Duluth, Ga
Contact:

Repairing your Fuel Sending Unit

Post by Briano1234 » Wed Jun 03, 2015 12:13 pm

Is it your Gauge or your Sending unit....
Well it is an easy test.
Remove the rear seat.
Remove the inspection cover.

Pull the Plug off the sending unit.
Jumper the Violet/Black pin on the connector to the Brown Ground pin.
Turn the Key on, as the plug is disconnected the fuel pump won't run.
Watch the Fuel gauge needle if it full deflects (registers full) It isn't your Gauge or the wire to it or possibly even the Sending unit.

First.
If your car has a solid state Speed Sensor attached to the Speedo, un clip it and remove the mylar.
Check your gauge. There are 3 types of sensors that I have run across, on the later 90's that originally had a Aktive Stereo, they used a solid state
Sensor. If that is Flaky, then your Gas Gauge may read 1/4 off.
Second. Replace is the 10V Stabilizer, even if your Water Temp gauge is acting normal, replace it.

If the Gauge is now functional STOP.


Repairing your Fuel Tank Sending unit.

Follow the Steps in How to Change your in-tank fuel pump 84.5-93.
http://volkswagenownersclub.com/vw/show ... -fuel-pump

Test the sender. With the Plug facing you, place a Ohm Meter 2K scale on the ground pin of the plug, that is the far left.
The other lead goes on the pin that is furthest to the left.

Here are Senders out of a Jetta, that I am using as a test.
Maximum resistance or EMPTY.
Image

Half full
Image

Full
Image


As you move the float arm up or down you should see 33-300 ohms resistance from full up to full down. 300 ohms is empty, 256 to 300 actually, and 33 ohms is full or the flat arm fully up. If that is what you have, then replace the thing back in the tank as your issues are else wheres.

There are little Tabs that hold the cover plate that holds the Float arm to the rheostat.
Image

Image

Carefully bend them back I use end nipper pliers.

Image

Image

Carefully lift it off, don't drop that copper spring.

Image


Remove the Float arm and place that copper spring on something white.

Image

Clean the brush on the float with some 2000 grit and you can even bend it a wee bit to make better contact.
Image

Here is the sending Rheostat, it is black with tarnish.
Image

Image

Using Q-Tips, and Alcohol, Gently rub it to clean the corrosion.
Image

Image

Once it is all clean I usually scrub it up and down in opposite direction to arm travel.
Reassemble the float arm and spring

Image

Reposition the cover holding it all together, position it so it is tight and Crip the tabs back over tight….

Image

You can plug it pack on to the connector and test it by re-connecting the battery and fuel pump connector, then turn on the keys, BE WARNED THE PUMP WILL SPIT GAS WHEN KEY IS ENGAGED SO HAVE RAGS HANDY and NO SMOKING OR OPEN SPARKS/ FLAMES.

Moving the float arm from one stop to the other your Gauge should now be working more better.
If you aren't happy with the FULL or EMPTY, you can bend those arms in or out that the float stops on.
Image


Return to the thread
http://volkswagenownersclub.com/vw/show ... -fuel-pump

For reinstallation…..


If your Gauge is still not registering totally full then the issue is usually in the instrument cluster, and that it i either the 10V stabilizer, Gauge, or connections. So first step is to clean the nuts holding the Gauge to the mylar.

You can apply a 9V battery across the nuts to see if the gauge will deflect full.
If it does then it is the connectors, or the 10V stabilizer.
If it doesn't then it is the Gauge.

To replace the Gauge see my How to fix a flaky water temp gauge to disassemble the Cluster.
viewtopic.php?f=27&t=2042

Fuel Gauge

Here is the Fuel Gauge out of the cluster.

It is similar to the Water Temp gauge as far as it is a nicachrome wire wrapped on a bimetallic spring.

Image

Its construction is different.
To remove the Face plate you have to file off the rivets on the back.

But usually it doesn't go bad as far as a cold solder joint goes as the wire is
Wrapped over the studs then affixed with "hot" melt glue?".

It is interesting to not that the two arms that suspend the needle are adjustable for the needle deflection or Stop. You can adjust them for the needle movement to
Be above or below the desired stop, that is full or empty.

To test the Gauge you need 10 volts and a ground, a 9vdc battery will full scale deflect. But don't leave it on too long as the needles wire will turn in to a toaster oven. It uses millivolts of current…

Image

The gauge works as this.
The needle is connected to both spring arms. Those arms are tied to the positive and negative posts.

The Needle is the "short" between the positive, and negative.
if you watch the movement under power you will see the wire heat up and cause the needle to pivot.

There isn't really much you can do to the gauge but solder the connections of the wires if they are broke.


All this started because one of my BLOND daughters would run the car out of GAS. She said well when I filled it up it registered 3/4 of a tank, so when the gauge was in the red, I still had 1/4 of a tank left....... DOHHHHHHHHHHHHHHHHHH.
Briano

Yes as matter of fact, I have the Luck o'the Irish...everything I touch turns to fertilizer of the bovine variety.
You can lead a user to a link, but you can't make him Click.... :screwy:

Post Reply