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Re: HELP PLEASE with fuel gauge/sending unit
Lee7673 #535883 February 02nd 2012 11:45 pm
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Lee7673 Offline OP
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AGHHHHH......after replacing (and checking) everything else, I believe the new sending unit I just installed is defective and is the culprit. Looks like I will dropping the tank again this weekend!!!!

Re: HELP PLEASE with fuel gauge/sending unit
Lee7673 #536066 February 03rd 2012 2:17 pm
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bummer man. Sorry to hear that, but glad you're persistant!




Re: HELP PLEASE with fuel gauge/sending unit
Lee7673 #536664 February 05th 2012 10:36 pm
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OK....here is the update and it is driving me nuts!!!! Hopefully someone will have some input or an idea. I ran every test and scenario that I could think of and it all kept leading me back to a bad sending unit (even though the sending unit and tank were brand new). So....I got another sending unit and dropped the tank (again) to replace it. When I pulled out the new sending unit it worked (I hooked it up to the gauge) but wouldn't work in the tank. I installed the new sending unit (I did check to make sure it was working before I installed it) and my fuel gauge only comes up to "E" (I have 15 gallons of fuel in it). I have tried to isolate everything to find the issue. I ran a new hot lead direct from the battery to a limiter, a new ground wire direct from the battery to the sending unit (trying to eliminate a bad wire), a new wire from the sending unit to the gauge and it still will only go up to "E". So....it appears that both of the new sending units work but NOT when installed in the tank). Why??? Also...one other thing...if I wire the gauge up without the voltage limiter the gauge reads correctly. I did this the first time when I had 3/8 of a tank and it would read empty when hooked up through the circuit board but would read 3/8 when hooked up to 12 volts (which is what it should have read with the amount of gas I had). I tried it again today and now it reads empty when hooked up correctly but will read about 5/8 of a tank when hooked up to 12 volts (which would be correct with the amount of fuel I have in it now). Why would the gauge read correctly when hooked up direct? I know it is supposed to run at 5 volts coming out of the limiter. My friend and I have probably spent 12 hours (or more) trying to figure this out....including dropping the tank twice, replacing the sending unit twice, changing out voltage limiters, and even trying 3 different gauges and I always get the same results. What am I missing? I REALLY need some help.....its driving me NUTS!!!!
Thanks....

Re: HELP PLEASE with fuel gauge/sending unit
Lee7673 #537086 February 07th 2012 10:36 am
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I'm trying to picture what your doing to test it before you put it into the tank. Are you hooking it up to the wires that are in the tank for testing or are you just hooking it up someplace after tank but before the gauge?

If it's working hooked up to the tank wiring before you put it in the tank but not after, you have a break in the wire that's making momentary connection or a bad plug in line just before tank.


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Re: HELP PLEASE with fuel gauge/sending unit
Lee7673 #537499 February 08th 2012 3:10 pm
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This is the reason most people hate automotive wiring.

I'm just grasping at straws here, but what about grounds? Is it possible that with the sending unit installed in the tank and the tank in place, you are loosing a ground or creating one where there shouldn't be one?

I remember my 73 Cuda had a braided wire with 2 clamps on it that clipped to the fuel sender line and to the line running to the carb. An old timer told me once it was to balance the voltage for the sending unit to work properly. Don't know if he was right or not though.


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Re: HELP PLEASE with fuel gauge/sending unit
Lee7673 #537554 February 08th 2012 5:52 pm
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Mopar sending units are grounded via the fuel line running up to the engine. That jumper strap must be in place for it to work.

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Nate Breece
Re: HELP PLEASE with fuel gauge/sending unit
NateB #537568 February 08th 2012 7:17 pm
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Lee7673 Offline OP
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Originally Posted by NatetheskateNCBV
Mopar sending units are grounded via the fuel line running up to the engine. That jumper strap must be in place for it to work.

[Linked Image]


Nate,
This is after market tank and sending unit. Its a Spectra sending unit (its the only after market brand I could find and I couldn't find a NOS one). The sending unit has three things coming out of it: a fuel line, a connection for the wire going to the gauge cluster and a tab with a wire coming off of it with a ring at the end for grounding (which I have grounded to the chassis). Do I still need the jumper strap?
Thank you in advance...I appreciate all of your input.

Re: HELP PLEASE with fuel gauge/sending unit
Lee7673 #537597 February 08th 2012 8:24 pm
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I have rebuilt my own sending unit in my 75 , same sending unit, anyway it is easy as bending a few tabs and opening up the little box and see if the rheostat is making contact with the finger that is supposed to be doing just that or do like Nate says and put the old one in, best bet if there are no new ones from your dealer. I know there are about three left for the Phoenix vintage FOS from Dodge at stock price. I got one for my tank Change. IF push comes to shove I have another brand new '86 tank and you can get a stock sending unit for it and just bring your wires around to the side of the tank and hook it up. Dodges are all the same set up even my 86 tank is dimpled for the right rear dump of the older models. They were pretty good about making easy changes. Good luck, Just an after mkt glitch I am sure


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Re: HELP PLEASE with fuel gauge/sending unit
Lee7673 #537645 February 08th 2012 11:05 pm
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Lee7673 Offline OP
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I spoke with a mechanic tonight and he thinks the tank might be positively charged (due to all of the excess wiring in the van....a wire might have been hit with a screw...he had 4 batteries in the van....its a mess). He said if it was it would only take a couple of millivolts to cause the gauge not to work.
Thoughts?

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