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Ancora Imparo
 
Join Date: Jan 2018
Posts: 151
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Help with fuel gauge

82SC with a fuel gauge issue:

Iíve owned the car for a few months and Iíve been going over it working out some minor issues. The fuel level was not reading correctly when I got the car, and I replaced the fuel sender based on feedback from forum members and threads here. That fixed the issue and the fuel level appeared to register accurately.

I recently went through my front fuse panel and cleaned it up, removing some corrosion and replacing all the fuses with new ones. Now Iíve noticed that the fuel level is jumping around frequently. It doesnít happen all the time or with any pattern that I can see. My first thought is that itís a grounding or connection issue and I plan to remove the gauge and clean up all the connections on the back. I should probably locate the ground connection to the chassis and clean that up too.

My questions:
- where is the chassis ground for the fuel gauge?
- which fuse location handles the connection for this gauge or all gauges?
- what other potential explanations are there for my issue?

Iíve made a couple videos of the fuel gauge jumping so you can see for yourselves. This is while the car is simply parked on level ground and idling:

https://www.dropbox.com/sh/flb4uo4dwv3g57q/AADNSTJZWOkYAjnejcyyhGBxa?dl=0
Old 06-11-2018, 08:09 AM
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ROW '78 911 Targa
 
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Gauge grounds are behind the dash all go to one bolt.
Clean the female contacts in the tank sender connector first.
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Old 06-11-2018, 08:50 AM
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Ancora Imparo
 
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Good advice, thanks. What’s the best way to clean the female contacts on the sender? Some small gauge bore brush? Has to be much smaller than a .22.
Old 06-11-2018, 08:58 AM
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The Mighty Pieholio
 
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Quote:
Originally Posted by Gretz View Post
Good advice, thanks. Whatís the best way to clean the female contacts on the sender? Some small gauge bore brush? Has to be much smaller than a .22.
I remember reading about guys cleaning their fuse contacts with a stubby #2 pencil chucked up in a drill. They used the eraser to clean the contacts.
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Old 06-11-2018, 09:28 AM
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Ancora Imparo
 
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Good idea. I have a Dremel- I’ll have to see if they make some kind of attachment that can be used for that purpose. Seems like a no brainer.
Old 06-11-2018, 09:37 AM
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Ancora Imparo
 
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I cleaned out the contacts between the new fuel sender and the female plug. They weren’t visibly corroded but I still cleaned them anyway. No luck. I assume I should check the ground next. Based on the Bentley wiring diagram, the fuel gauge grounds to G2 which is says is behind the heater controls. I don’t see it back there. I’m assuming I have to pull a gauge to get at it? Anyone have a photo of that location?
Old 06-13-2018, 04:24 PM
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Ancora Imparo
 
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Bumping this. Anyone know the exact location of the ground behind/under the dash? A photo would be great.

Also, which fuse in the fuse panel handles the fuel gauge?

Thanks!
Old 06-14-2018, 07:45 PM
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Just a thought after reading this thread.

Your problem began after you, "went through my front fuse panel and cleaned it up, removing some corrosion and replacing all the fuses with new ones." It's quite possible that the fuse for the fuel gauge is not set correctly or the contacts on each side are a bit loose allowing intermittent/poor contact. Once you locate the proper fuse, a close look at how it's set may uncover something.
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Old 06-15-2018, 07:38 AM
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Just a thought. You could always add a new ground to your sending unit as a temp measure to see if it indeed fixes your problem. You could put it to the negative post on the battery so no extra holes are drilled anywhere.
Old 06-15-2018, 07:42 AM
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Ancora Imparo
 
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These are good ideas. I will go back through the fuse panel and check it. Even reviewing the Bentley manual I can’t figure out exactly which fuse it is so I’ll have to check them all and perhaps add some dielectric grease, which I didn’t use last time. I’ll do the same with the rear fuse panel.

Also, I found a tip on another thread about shorting out a pin to get the gauge to go to max to confirm it functions correctly. I filled up yesterday and the level seems to be generally correct so it does seem to be working. But it still jumps around a bit.

When I turned the car off yesterday the level did not drop to the bottom. Then I tapped the gauge with my finger and it dropped to empty. Seems like that would suggest a bad gauge. Thoughts?

And I still can’t get a good idea of the exact location of the dash ground, G2, so if anyone knows that please chime in. Thanks.
Old 06-17-2018, 10:16 AM
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