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After market fuel gauge

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davester304 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote davester304 Quote  Post ReplyReply Direct Link To This Post Topic: After market fuel gauge
    Posted: Aug/07/2018 at 11:01am
After not having a working fuel gauge since I got my Javelin I decided to run an aftermarket gauge that would fit into my existing 3 gauge pod under the dash. 

Just a quick question ( as I am not having much luck getting it to work). 

Does the ground from the new gauge need to run to the ground on the sending unit? As it is now, there is a ground from the sending unit and a ground from the gauge that are separate. In this configuration, I am only getting a slight reading on the new gauge when I switch the power on - it goes from the empty peg to just under empty. I have run a new sending unit wire all the way from the gauge to the sender, and have it powered to come on with the key on/running. Thoughts? Thinking maybe I will check the chassis ground next. Yes, the new gauge is compatible with AMC specifications although the sending unit is new- but assume it has the same specifications as the old one i.e. ohms readings at empty and full. Oh yes, there at least 1/2 tank of gas in it! 

Thanks for any info! 
1970 Javelin SST
If you don't look back at it when you park it, you bought the wrong car
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Post Options Post Options   Thanks (1) Thanks(1)   Quote bigbad69 Quote  Post ReplyReply Direct Link To This Post Posted: Aug/07/2018 at 4:53pm
The OE gauge does not have a ground at the gauge - it's at the sending unit. If the replacement is indeed compatible with the OE system, then it shouldn't need one either. I suspect the ground on the gauge is for the light. Definitely verify the ground at the sending unit. That is often the cause of a non-functioning fuel gauge. It helps to use a tooth washer under the ground terminal to cut through the paint/rust/undercoating on the chassis.

The standard test for the OE gauge is to touch the sense wire to the chassis (ground). That will peg the the needle at full. If it does, suspect the sending unit. If it doesn't, then the problem is with the gauge or the sense wire or power to the gauge. Read the instructions and make sure a 0 ohm sense will not damage the meter before attempting this test on your aftermarket gauge.

Also check your battery connection to the engine and engine to block. The gauge is a low resistance system (10 -70 ohm). Any resistance due to dirty connections will cause the needle to be lower than expected.

Is your temperature gauge working? If not, it could be the IVR that is the problem.

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Post Options Post Options   Thanks (1) Thanks(1)   Quote 6768rogues Quote  Post ReplyReply Direct Link To This Post Posted: Aug/07/2018 at 6:46pm
Your aftermarket gauge should have hot, ground, and sending unit connections, in addition to hot and ground for the light. Hook the sending unit terminal to a wire to the sending unit. The gauge has hot and ground so it can come alive when you turn on the car. The sending unit gives a variable resistance to ground and that resistance is read by the gauge to put the needle in the right place.  

Edited by 6768rogues - Aug/07/2018 at 6:50pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote davester304 Quote  Post ReplyReply Direct Link To This Post Posted: Aug/10/2018 at 4:27pm
No luck grounding or un-grounding the gauge as was suggested. I checked with the company that I got the new sending unit from and they say it is indeed a 10/73 ohm rating - which would be the same as original, and also matches the rating of the new gauge ( Equus 7361 - 10/73 ohms) ... so for now, I still don't have a working fuel gauge - but have lived without it for now so will keep living without it Big smile ! 

Will have a look at it again in a few weeks when our show season is over. Thanks to all for the input.




Edited by davester304 - Aug/10/2018 at 5:58pm
1970 Javelin SST
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addic View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote addic Quote  Post ReplyReply Direct Link To This Post Posted: Aug/10/2018 at 8:14pm
 try grounding the wire going to the fuel sender ,yellow I think and when ground, the gauge should start to rise and peg full,if this happens then you know fuel sender in tank not working.
but if it does not do anything something else ,also use a light tester and hook up to yellow wire at tank and light should flicker 
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73 401 Pierre Cardin X F3     70 X 390 4spd
69 X 401 6 spd
69 AMX 401 auto BSO
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Post Options Post Options   Thanks (1) Thanks(1)   Quote addic Quote  Post ReplyReply Direct Link To This Post Posted: Aug/10/2018 at 8:17pm
another thing I found out with the original fuel gauge was the nuts holding gauge needing tightening on back of cluster
73 401 Pierre Cardin X P1
73 401 Pierre Cardin X F3     70 X 390 4spd
69 X 401 6 spd
69 AMX 401 auto BSO
73 AMX 401 4speed pc
73 vette 427sb 5spd
73 vette convt.?
08 zx14
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davester304 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote davester304 Quote  Post ReplyReply Direct Link To This Post Posted: Aug/23/2018 at 10:52am
So, here's a bit of an update for y'all.
I got a multi meter and checked the ohms on a spare 71 Javelin fuel sending unit I have, and got the perfect 8 - 70-ish range on it. (factory is 10/73) so I know it works. 

I checked the sender in my car knowing there is about 1/2 tank of gas in it. ( I didn't remove the sender, just wanted to see what the reading would be) and it came in at 80 ohms resistance! That reading is over what it should be either empty or full. 

Last week I emailed the supplier that I bought the sending unit from to ask if they could confirm the sending unit ohm range was indeed 10/73 - and they assured me that it was. 

So, should I replace the new 10/73 ohm fuel gauge I just bought, and get a different gauge with a greater range - there are a couple of options, or do you folks have a different idea that I am missing? 

Thanks for feedback! 
1970 Javelin SST
If you don't look back at it when you park it, you bought the wrong car
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nickleone View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote nickleone Quote  Post ReplyReply Direct Link To This Post Posted: Aug/23/2018 at 11:24am
More info needed. Sender make, model and part number.
Who did you purchase it from.

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Post Options Post Options   Thanks (1) Thanks(1)   Quote jpnjim Quote  Post ReplyReply Direct Link To This Post Posted: Aug/23/2018 at 1:57pm
I would want to keep the gauge if it works, and replace the out of spec sending unit.

Lots of people have complained about brand new, bad sending units,
so the one you have may not work with any gauge.
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was Green/green now T/A red w/blk leather

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Post Options Post Options   Thanks (1) Thanks(1)   Quote Someassemblyrqd Quote  Post ReplyReply Direct Link To This Post Posted: Aug/24/2018 at 11:02am
Since you’ve confirmed your spare sending unit is accurate, why not put that unit into the vehicle? Sounds like a match to your gauge.
Greg E.
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