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Fuel Gauge Erratic

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John Cotner View Drop Down
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    Posted: 30 July 2021 at 6:15am
I just replaced the fuel gauge and sender on my '46 CJ2a.  I tested the sender unit ut of the tank and all works well.  When I turn on the key the gauge reads accurately.  When I start the engine the fuel gauge reads accurately at idle, but when I apply power it goes to full no matter how much fuel is in the tank.  When I stop at a light and the motor goes back to idle the gauge reads accurately again. 

This is more a minor inconvenience than a serious problem since I don't drive long distances, but I want to make sure there isn't some larger electrical problem lurking.
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John Cotner
New Ulm, Minnesota
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TERRY Quote  Post ReplyReply Direct Link To This Post Posted: 30 July 2021 at 10:23am
What voltage gauge did you get?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote John Cotner Quote  Post ReplyReply Direct Link To This Post Posted: 30 July 2021 at 12:24pm
Six volt.  I have a six volt system.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TERRY Quote  Post ReplyReply Direct Link To This Post Posted: 30 July 2021 at 1:58pm
Chech the voltage output, sounds like the charging system is at fault.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote John Cotner Quote  Post ReplyReply Direct Link To This Post Posted: 31 July 2021 at 6:30am
Where is the best point to check?  The generator is a somewhat recent rebuild from the PO.  The regulator doesn't look original but is pretty old.
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John Cotner
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMusil Quote  Post ReplyReply Direct Link To This Post Posted: 31 July 2021 at 7:08am
Hook a meter up to the battery.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote John Cotner Quote  Post ReplyReply Direct Link To This Post Posted: 31 July 2021 at 8:36am
I'll hook a meter up to the battery.  I'm guessing check voltage while engine is off, at idle, and at 1000 rpm or so.  What are the correct parameters for a six volt system?
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John Cotner
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TERRY Quote  Post ReplyReply Direct Link To This Post Posted: 31 July 2021 at 10:46am
At least 2000 rpm or more to evaluate regulator output. Leave the lights off in case the voltage is real high as 6v bulbs will fail. Maybe PO had a 12v generator built??
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Post Options Post Options   Thanks (0) Thanks(0)   Quote John Cotner Quote  Post ReplyReply Direct Link To This Post Posted: 31 July 2021 at 12:04pm
Battery voltage with engine off: 6.49
Battery voltage at idle (640 rpm) engine warmed up: 7.05
Battery voltage @1000 rpm: 8.26
Battery voltage @2000 rpm: 8.18

I noticed when revving the engine from idle the ammeter pegs up to 40, then settles down to just on the plus side of center. 
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John Cotner
New Ulm, Minnesota
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TERRY Quote  Post ReplyReply Direct Link To This Post Posted: 31 July 2021 at 12:38pm
Regulated voltage spec is 7.1 to 7.3. The manual describes how to adjust the regulator (section I). Or,  a new reg is a Standard Motor Products VR2.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TERRY Quote  Post ReplyReply Direct Link To This Post Posted: 31 July 2021 at 1:39pm
I forgot to mention, all connections between the generator and regulator should be checked for cleanliness, shorts, opens, and a proper ground from reg to generator.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote John Cotner Quote  Post ReplyReply Direct Link To This Post Posted: 31 July 2021 at 2:27pm
Looks like my regulated voltage is a bit high.  I'll check the manual to see if it can be adjust within spec.
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John Cotner
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