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Cheburashka
Samba Member
Joined: July 10, 2018
Posts: 112
Location: WA
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 Posted: Thu Aug 16, 2018 7:18 am Post subject: Fuel gauge swinging right to left. Also question about sender. |
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The fuel gauge on my '71 SB is misbehaving. The tank was filled less than 20 miles ago. It sometimes reads "empty" upon startup, and sometimes swings over to the middle range. When I'm driving, it will swing over to about 2/3, then back to "empty" over and over again as I drive. I've cleaned the electrical connections and the ground for the vibrator, but it continues to do this. The sender winding was warped, but I heated it and brought it back as close to flat as I could get it and it appears to make good contact all the way through the range. Any ideas what might cause it to do this?
Also, why does the SB gauge have two floats? I didn't see a "refill" light, but maybe I just don't know where to look. Can different sender be used? The SB ones are quite expensive.
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gt1953
Samba Member
Joined: May 08, 2002
Posts: 13848
Location: White Mountains Arizona
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| Posted: Thu Aug 16, 2018 7:30 am Post subject: Re: Fuel gauge swinging right to left. Also question about sender. |
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Check all of the associated connections. I have had loose fuel gauge connections do the very same thing.
_________________
Volkswagen: We tune what we drive.
Numbers Matching VW's are getting harder to find. Source out the most Stock vehicle and keep that way. You will be glad you did.
72 type 1
72 Squareback
({59 Euro bug, 62, 63, 67, 68, 69, 73 type ones 68 & 69 type two, 68 Ghia all sold}) |
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mark tucker
Samba Member
Joined: April 08, 2009
Posts: 23937
Location: SHALIMAR ,FLORIDA
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| Posted: Thu Aug 16, 2018 9:57 am Post subject: Re: Fuel gauge swinging right to left. Also question about sender. |
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| my stdb has always done that. |
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ashman40
Samba Member
Joined: February 16, 2007
Posts: 15982
Location: North Florida, USA
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| Posted: Thu Aug 16, 2018 12:11 pm Post subject: Re: Fuel gauge swinging right to left. Also question about sender. |
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| Cheburashka wrote: |
| The fuel gauge on my '71 SB is misbehaving... It sometimes reads "empty" upon startup, and sometimes swings over to the middle range. When I'm driving, it will swing over to about 2/3, then back to "empty" over and over again as I drive. I've cleaned the electrical connections and the ground for the vibrator, but it continues to do this. The sender winding was warped, but I heated it and brought it back as close to flat as I could get it and it appears to make good contact all the way through the range. |
My first guess would be a bad fuel vibrator. Considering that the sender SHOULD show LOW every time you take a turn as the fuel moves to one side of the tank, haven't you wondered why the gauge needle doesn't normally bounce all over the place? The reason it doesn't is due to the fuel gauge vibrator. The function of the vibrator is to dampen the changes in the resistance coming from the fuel sender. It does this by pulsing the INPUT voltage to the fuel gauge with the vibrator (early pulse width modulation - PWM). If the internal contacts of the vibrator were fused together and the voltage thru the vibrator was the same as the ignition voltage, the gauge readings would bounce all over the place.
I don't recall if there is a test for vibrators?
| Cheburashka wrote: |
| Also, why does the SB gauge have two floats? |
STD Beetle tank (bottom):
SB tank (bottom):
Note that the SB tank has a smaller area bulging from the bottom. While both tanks are generally the same size at the top (which would affect the rate that the float moves when the tank is near full), as the fuel level drops into the different sized bulge area the level of the fuel will change faster because the volume contained in the SB tank bulge is smaller. The SB fuel sender needs to treat the rate of fuel change near the bottom differently than near the top. This is why there are two floats and on different length arms and while BOTH change when the tank is near full, only one changes height near the bottom of the tank.
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AshMan40
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'67 Beetle #1 {project car that never made it to the road  }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!} |
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