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Fuel Sender vs Fuel Gauge
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wit61
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PostPosted: Tue Mar 31, 2020 9:20 am    Post subject: Fuel Sender vs Fuel Gauge Reply with quote

Dear Wizards and Gurus,

My fuel gauge does not work (temp gauge works fine), and I first did the instrument cluster connector prongs. No change. I reluctantly decided to replace the fuel sender. Once out, I decided to test the suspect sender. Per the helpful thread below, and the video link below that, it seems to be ok. A caveat is that I was not simulating a true floating in liquid scenario. 2 questions:

1. Is there an easy way to simulate the sender on full via the plug at the tank, so that I can test the pathway back to the gauge?

2. Where would you look next if a new sender does not solve the issue ?

https://www.thesamba.com/vw/forum/viewtopic.php?t=674431



Link

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Steve M.
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PostPosted: Tue Mar 31, 2020 9:26 am    Post subject: Re: Fuel Sender vs Fuel Guage Reply with quote

Check voltage going to the fuel gauge.
It is an unlikely problem as your temp gauge is working, but they do not use 12v like the rest of the car.
There is a voltage stabilizer on the backside of the instrument panel that reduces the 12v to 10 volts for these gauges.

It looks like this:
https://www.vancafe.com/171919803-p/171919803.htm

As I said unlikely since the temp gauge is working, but I would check the voltage at the fuel gauge.
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MarkWard
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PostPosted: Tue Mar 31, 2020 9:34 am    Post subject: Re: Fuel Sender vs Fuel Guage Reply with quote

With the key on temporarily ground the purple and black wire at the sender. The fuel gauge should begin to climb. Stop before recording full. If this test passes, jump the sender plug and you should have the same result. If not, itís a ground wire problem. If it works, then the sender is the problem. I would plug the sender back in and turn it upside down. You donít need liquid. Upside down gauge should read full assuming the above tests work. PS I might be wrong about the wire color. I didnít look it up.
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Steve M.
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PostPosted: Tue Mar 31, 2020 9:41 am    Post subject: Re: Fuel Sender vs Fuel Guage Reply with quote

^^^ We should be making a sticky of all the collected tidbits of the working experience you have!

Very Happy
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valvecovergasket
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PostPosted: Tue Mar 31, 2020 1:10 pm    Post subject: Re: Fuel Sender vs Fuel Gauge Reply with quote

wit61 wrote:

1. Is there an easy way to simulate the sender on full via the plug at the tank, so that I can test the pathway back to the gauge?


yes!

you need a decade box, and can then walk the gauge through the entire sensor sweep step by step.

you can get a cheap(ish) one on amazon or ebay, since percision requirement here is pretty limited. but its a great way to back-test gauges/sensors, etc
awesome tool to have in the box


i actually had this exact issue on a different project car about a year ago, a fuel level sender v. fuel gauge check. decade box helped narrow it down in about 10 minutes.
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wit61
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PostPosted: Tue Mar 31, 2020 3:32 pm    Post subject: Re: Fuel Sender vs Fuel Gauge Reply with quote

This is why this forum is invaluable !!

First I reconnected the intake hose to fuel so that the pump would not suck air. Then I took MarkWard's advice (thanks) and grounded the purple/black wire. Like magic, the gauge responded. Then I bridged the terminals and it also worked. This led me back to the sender. A head scratcher since it seemed to test ok.

Conveniently, the mailman showed up a day early with my new sender. I installed it, and the problem is solved.

I have to conclude that my bench test of the old sender (see video) somehow produced a false positive. I have had no fuel gauge for a while. Not intermittent, consistently none. Another diagnostic lesson learned.

Thanks all.
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PostPosted: Tue Mar 31, 2020 3:51 pm    Post subject: Re: Fuel Sender vs Fuel Gauge Reply with quote

A result. Glad you got it solved.
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PostPosted: Tue Mar 31, 2020 9:07 pm    Post subject: Re: Fuel Sender vs Fuel Gauge Reply with quote

Not relevant to the original poster but figured I'd stick this info here for future searches on unknown reasons why the fuel sender does not work.

My doka fuel sender never worked since I picked it up from the docks over two years ago. Since then I have removed the sender and tested it - all good; Checked the blue foil at the cluster, seemed to be good; Cleaned the ground in back - still no go. I assumed the wire must be damaged somewhere and left to it that. Last week on dropping my relay/fuse holder yet again for another re-wire mod (headlight relays) I discovered this violet/black wire floating about -
Image may have been reduced in size. Click image to view fullscreen.


I could not tell where it escaped from so after referencing the the wiring chart for about an hour looking for that color violet/black combo (my '91 chart is in German so translating as I went looking for any li/sw reference) - found that the fuel sender is that combo and belongs in the white E Block in pin 5. Some wiggling to get E block out; well placed super glue so as not glue E block down permanently; re-inserted the E block and now gauge works. Yay!
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wit61
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PostPosted: Thu Apr 02, 2020 4:33 pm    Post subject: Re: Fuel Sender vs Fuel Gauge Reply with quote

Alaskaberrys wrote:
Not relevant to the original poster but figured I'd stick this info here for future searches on unknown reasons why the fuel sender does not work.

My doka fuel sender never worked since I picked it up from the docks over two years ago. Since then I have removed the sender and tested it - all good; Checked the blue foil at the cluster, seemed to be good; Cleaned the ground in back - still no go. I assumed the wire must be damaged somewhere and left to it that. Last week on dropping my relay/fuse holder yet again for another re-wire mod (headlight relays) I discovered this violet/black wire floating about -
Image may have been reduced in size. Click image to view fullscreen.


I could not tell where it escaped from so after referencing the the wiring chart for about an hour looking for that color violet/black combo (my '91 chart is in German so translating as I went looking for any li/sw reference) - found that the fuel sender is that combo and belongs in the white E Block in pin 5. Some wiggling to get E block out; well placed super glue so as not glue E block down permanently; re-inserted the E block and now gauge works. Yay!


I checked the connector first since the fuel sender job is such a PITA. My violet/black was in place, but I took the opportunity to tweak all of those little prongs so that they make good contact. Glad yours was an easy fix.
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