Fuel gauge needle jumped UP while sitting idling??

[Rob Mayercik]

Ok, this was a bit weird:

Was sitting at a traffic light last night on the way home from work. Car was level front-to-back, but tilted slightly to the right, and I'd been sitting stationary for at least 20 seconds. I happened to be looking down at the cluster, and noticed the fuel gauge needle start to "wobble" up and down very slightly.

As that registered in my brain as odd, the darn thing actually jumped up almost all the way to the next hash mark (was at the 1/4 mark, so it jumped up to the 3/8 mark), then proceeded to sink back down and settle about half-way between the two marks, which meant it was reading about 1/16 of a tank higher than it was 5 seconds before.

Since one of my usual fueling points was just up the block after I got the green light and made my turn (was a "no turn on red" intersection), I pulled in and filled up just to be safe as I was about a mile into my 50-mile run home. Car took 13.3 gal fully vented (with trip odo at 565.5 miles), so the gauge reading turned out to be pretty much correct, but I don't think I've ever happened to notice that happening before.

This isn't the car's original sender, but it's been in the car since October 2002. Could this be a sign of a dirty ground, or maybe that the sender might be starting to fail?

 

[BobnOH]

I guess between opening the tank to check the sender and getting at the cluster connects, I'd look in the tank.

 

[Sauaciden]

C

Ok, this was a bit weird:

Was sitting at a traffic light last night on the way home from work. Car was level front-to-back, but tilted slightly to the right, and I'd been sitting stationary for at least 20 seconds. I happened to be looking down at the cluster, and noticed the fuel gauge needle start to "wobble" up and down very slightly.

As that registered in my brain as odd, the darn thing actually jumped up almost all the way to the next hash mark (was at the 1/4 mark, so it jumped up to the 3/8 mark), then proceeded to sink back down and settle about half-way between the two marks, which meant it was reading about 1/16 of a tank higher than it was 5 seconds before.

Since one of my usual fueling points was just up the block after I got the green light and made my turn (was a "no turn on red" intersection), I pulled in and filled up just to be safe as I was about a mile into my 50-mile run home. Car took 13.3 gal fully vented (with trip odo at 565.5 miles), so the gauge reading turned out to be pretty much correct, but I don't think I've ever happened to notice that happening before.

This isn't the car's original sender, but it's been in the car since October 2002. Could this be a sign of a dirty ground, or maybe that the sender might be starting to fail?

Could be dying cluster. If you have vcds run cluster test to see if gauge is working at full range

 

[Rob Mayercik]

Yes, I do have VCDS. Will try to find time to pull out my trusty HEX-COM and do that this weekend.

 

[Rob Mayercik]

Update:

I was able to run the output test (had to dig out my ancient laptop and replace the CMOS battery, something's out of whack with the USB-RS232 adapter I use on my regular machine). When it got to the fuel gauge, it swept smoothly from bottom of range to top of range, then back down, then jumped up to a needle's width below exactly 1/2 tank, where it held until I moved onto the next part of the test. No stored codes in the cluster or anywhere else in the car, either - did a full autoscan.

I also popped the access cover for the tank. Besides finding a mess of nut shells/sunflower seeds that I had to vacuum out, not much to report here - the connector looked clean and the wires OK (though I did cycle the connector on and off a couple times to "polish" the contacts). Did this before running the output test. Oh, and I learned that I have a "Rev D" sending unit (caught my eye because I was re-reading the thread about the updated ones that eliminated one of the check valves as a "cold weather fix" recently).

Guess I will continue to monitor the gauge and see if it does it again.

 

[STDOUBT]

Just FYI Rob, when i replaced my sender with a newer revision, I found that while the check valve 'ball' was not included,
the little 'cage' that keeps the ball within a certain travel space is still present. I went ahead and drilled it out just
to make sure that little feed tube was all clear.

 

[JB05]

My fuel gage has a tendency to drop down one or two hash marks from time to time. It has always done this; both OEM and replacement in-tank pump and sender assemblies. I took apart the cluster and swapped in a different sender motor, but no change.

 

[Rob Mayercik]

I had the sender swapped twice back when the car was only a year or so old because it'd do that coming off a fill (drop off full to 7/8 and go back up), that's probably how I ended up with a "D" sender. I think the removal of the check valve ball is a later letter rev. Since I've not had any gelling/icing issues so far in 19 years/428,000 miles, I figure there's no hurry to do that drilling out...

At this point I'm going to chalk it up to "VW weirdness", I think. More concerned right now about figuring out why my USB-RS232 adapter stopped playing nice with my HEX-COM.