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BayCreamPuff
Samba Member
Joined: August 10, 2015
Posts: 769
Location: Oakland, CA
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 Posted: Mon Feb 08, 2016 12:31 pm Post subject: Fuel gauge sender terminal resistance |
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My fuel gauge is off by about 1/4 tank. I've replaced the vibrator, took out the sender and verified that it's functioning properly.
I think I've narrowed it down to extra resistance on sender terminal of the fuel gauge itself.
Sender wire resistance is at 35.3 with just over half a tank
Sender wire connected to terminal reads 22.5 at the terminal
Terminal resistance reads 61.2 without the wire connected
I would expect there to be some internal resistance, but 61.2 seems very high.
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Cream Puff
'79 CA Stock FI Deluxe Campmobile
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'87 GoWesty 2.2 Westfalia
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Tcash
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Joined: July 20, 2011
Posts: 12844
Location: San Jose, California, USA
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BayCreamPuff
Samba Member
Joined: August 10, 2015
Posts: 769
Location: Oakland, CA
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| Posted: Mon Feb 08, 2016 1:59 pm Post subject: Re: Fuel gauge sender terminal resistance |
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The gauge pegs when grounded and the sender is good (reads 70 when all the down down, 0-ish when all the way up).
I'm going to go fuss with it some more.
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Cream Puff
'79 CA Stock FI Deluxe Campmobile
Earl Grey
'87 GoWesty 2.2 Westfalia
Marsha Mellow
'00 Eurovan VR6 Full Camper |
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scrivyscriv
Samba Electrician
Joined: October 04, 2011
Posts: 2922
Location: Memphis
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| Posted: Mon Feb 08, 2016 6:16 pm Post subject: Re: Fuel gauge sender terminal resistance |
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I don't know if you can measure across the gauge and get any sort of meaningful reading to help with troubleshooting. Seems like if you're getting the full range of resistance from your float, the gauge needs to be adjusted.
Looks like you've got a late bay, I'm not too familiar with your setup but I do know the early bays and bugs have a calibration adjustment at the needle. Make sure your gauge ground is good.
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Robert in Memphis
Dünkelgrügen 1967 Java Green bug thread
Engine rebuild thread
If you're ever in the Memphis area, you are welcome to stop by for advice and help. |
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Wasted youth
Samba Member
Joined: July 06, 2012
Posts: 5134
Location: California's Hot and Smoggy Central Valley
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| Posted: Tue Feb 09, 2016 11:42 pm Post subject: Re: Fuel gauge sender terminal resistance |
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I'll probably get some crap for this, but I'll say it anyway. When I renovated my fuel system on the 1977 bus, I found the Ohms readings on my new sender did not match Ratwell's readings. I chalked this up to shitty QC on the new part, and not Ratwell's data. So what I did was run long jumper wires to have the circuit complete and energized with my gas tank and sender resting on saw horses. Then I simply bent the swing arm of the sender until the float level at its highest position gave me a 1/1 reading on the gauge, with sender locked into the tank. But this also caused the float to not quite reach the bottom of the tank. So when my gauge read R, I probably had about two gallons of gas left in the tank.
The process takes awhile, because the gauge vibrator has to pulse numerous times. This helps keep our gauges from wildly erratic readings due to normal fuel slosh, but you have to wait a couple minutes between each adjustment of the arm.
So this is sort of an improv suggestion for getting a decent tank reading when you have out of parameter Ohm readings. |
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scrivyscriv
Samba Electrician
Joined: October 04, 2011
Posts: 2922
Location: Memphis
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| Posted: Wed Feb 10, 2016 5:38 am Post subject: Re: Fuel gauge sender terminal resistance |
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That's actually more or less how you're supposed to do it 
No craps given haha
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Robert in Memphis
Dünkelgrügen 1967 Java Green bug thread
Engine rebuild thread
If you're ever in the Memphis area, you are welcome to stop by for advice and help. |
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Wasted youth
Samba Member
Joined: July 06, 2012
Posts: 5134
Location: California's Hot and Smoggy Central Valley
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| Posted: Wed Feb 10, 2016 7:44 am Post subject: Re: Fuel gauge sender terminal resistance |
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| Oh.. Ha! |
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BayCreamPuff
Samba Member
Joined: August 10, 2015
Posts: 769
Location: Oakland, CA
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| Posted: Wed Feb 10, 2016 3:54 pm Post subject: Re: Fuel gauge sender terminal resistance |
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The other day I pulled the gauge, vibrator and sender out to bench test. Noticed some dead spots on the sender so opened it up to find it fried and cracked. New sender ordered.
I was still reading 1/4 tank at the 33 ohms position on the bench though, so I imagine I'll need to continue to adjust things.
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Cream Puff
'79 CA Stock FI Deluxe Campmobile
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'87 GoWesty 2.2 Westfalia
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Wasted youth
Samba Member
Joined: July 06, 2012
Posts: 5134
Location: California's Hot and Smoggy Central Valley
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| Posted: Wed Feb 10, 2016 4:38 pm Post subject: Re: Fuel gauge sender terminal resistance |
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| There was a thread about rebuilding the fuel sender, if you are so inclined. |
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SGKent 
Samba Member
Joined: October 30, 2007
Posts: 41031
Location: Citrus Heights CA (Near Sacramento)
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| Posted: Wed Feb 10, 2016 4:39 pm Post subject: Re: Fuel gauge sender terminal resistance |
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I am sorry I missed this thread. That is normal. The original senders had a flat topped float that let them rise more. On all the late senders you have to bend the arm (not the stop) to let them read 1/4 fuller. That is just how it is. I went thru all NOS parts before figuring it out a couple years ago. Everyone with late senders has an issue where it reads 1/4 low.
pulled this from another thread on the issue. There are several threads on it.
| SGKent wrote: |
| chimneyfish wrote: |
SGKent is right, you need to bend the arm on the new units, even on the new VDO ones.
2010 thread here: http://www.thesamba.com/vw/forum/viewtopic.php?p=4576662
When I replaced my old VDO sender with a new VDO one, I simply lined the round cap of the sender that slots in the tank up with a shelf in the garage, think of the top of the shelf as being the top of your fuel tank, when you raise the float on the newly made modern units, it levers to above the top of where the fuel tank will be. (Switch your multimeter to Ohms, it will prove that there is still 1/4 of a tank full of travel left on the windings when the float is hitting the top of the tank).
What you need to do is bend the arm so that when the float reaches the end of how far the arm can travel, it is level with the underside top of the tank (i.e. just below the line of the top of the shelf / sender cap - hope that makes sense?).
Why do you have to do this to these new units? I think poor quality control, they are't made in Germany anymore, and they don't make them like they used to! Making minor adjustments to electrical instrumentation is quite a normal occurence, even with the best stuff.
Also, you need to compensate as the old floats had a flat top, the new floats cylindrical all the way around.
Here is an image of an old VDO sender, and a repro Flotamex sender posted by Pearl the party bus (which he sent back as it would not lock into the top of the tank):
http://www.thesamba.com/vw/forum/album_page.php?pic_id=250881
Here is a new VDO unit that you need to bend the arm on, otherwise 3/4 tank is the max you will ever read on the gauge:
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there are threads on the fix for this. All you need to do is adjust the arm so it reads full when up and the stop so it reads empty when down. |
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Tcash
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Location: San Jose, California, USA
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