Lotus Elan

Fuel gauge

PostPost by: Emma-Knight » Sun Nov 19, 2006 5:18 pm

When connecting my fuel gauge it always goes "bang" to full. :?
(tank is only 1/4 full) Green plus to B double terminal, green black to T single. ground to fixing bolt. Plus delivers 12.6 v from batterie. Green black resistance test against ground shows infinite resitance. Black ground works fine with instrument bulbs etc. B and T terminals changed over make the finger go "bang" to empty. Shouldn't be digital, should it?
My car has negative ground and worked this way before I took it apart... :wink:
How to bench test the instrument? Is the tank resistance device at high resistance on empty? Could a split green black line to the tank be the cause?


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PostPost by: john.p.clegg » Sun Nov 19, 2006 5:42 pm

Anna
I think you may have the wires crossed,the sender should be 20 ohms full,200 ohms empty (or thereabouts) and the other "tag" gives a full earth to illuminate the low fuel warning light...

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PostPost by: john.p.clegg » Sun Nov 19, 2006 5:46 pm

P.S.
The way to test is earth one then the other wire and see what happens to the guage(should rise to full),and the fuel warning lamp (should illuminate)

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PostPost by: types26/36 » Sun Nov 19, 2006 6:57 pm

[quote="Emma-Knight"
How to bench test the instrument? Is the tank resistance device at high resistance on empty? Could a split green black line to the tank be the cause?
Anna[/quote]

Anna,
A couple of weeks ago I fitted a new tank gauge to my Sprint (S4) and I checked the resistance, readings as followers:
Full: 20 ohms......+ - 2 ohms
Empty: 262 ohms ...+ - 2 ohms
I note you have an S2, a long time ago I tried changeing the Sprints unit with my S2's unit and it doesn't work.......well it works the wrong way round and it is wrong.
Read this thread which says they are different and work on a different resistance so I dont think the 262/20 ohms apply to your car.
http://www.lotuselan.net/forums/viewtop ... c&start=15
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PostPost by: Emma-Knight » Mon Nov 20, 2006 3:46 pm

:D
Following the link and the "inverted" theorie, I started measuring with a DC power unit: plus to B double terminal, minus to fixing bolt and a second plus (plus 2 :wink: )via 0 - 90 ohm resistor to T terminal. Resistance down -> 0 ohm: empty - resitance up about 50 ohm: about half full - more resitance - full.

The "dead" green black wire was resistance infinite so hard "bang" movement without damping to full.

Now I have to revitalize the wire connectors or the tank sender unit - which has been sitting on empty for about one year...

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PostPost by: fatboyoz » Tue Nov 21, 2006 2:07 am

Anna,
Do you have a voltage stabiliser connected to the fuel gauge?
Also, this thread (http://www.lotuselan.net/forums/viewtop ... c&start=15) says that there are two types of sender and only one type of gauge. The parts manual actually shows S1 to S3 sender and gauge part numbers to be different to S4 sender and gauge.
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PostPost by: fatboyoz » Tue Nov 21, 2006 2:08 am

Anna,
Do you have a voltage stabiliser connected to the fuel gauge?
Also, this thread (http://www.lotuselan.net/forums/viewtop ... c&start=15) says that there are two types of sender and only one type of gauge. The parts manual actually shows S1 to S3 sender and gauge part numbers to be different to S4 sender and gauge.
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PostPost by: Emma-Knight » Tue Nov 21, 2006 2:09 pm

It's the original set up with Lucas Voltage control box. This test was run on batterie only so voltage constant at 12.6 volt.

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PostPost by: Frank Howard » Tue Nov 21, 2006 4:53 pm

"Do you have a voltage stabiliser connected to the fuel gauge?"

Anna,

The voltage stabilizer is different from the control box (otherwise known as the voltage regulator). The fuel gauge should plug into the voltage stabilizer which is usually mounted on the back of the speedometer. It's a little metal retangular box with probably 5 connectors on it. Hope this helps.
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PostPost by: types26/36 » Tue Nov 21, 2006 5:18 pm

Frank Howard wrote:. The fuel gauge should plug into the voltage stabilizer which is usually mounted on the back of the speedometer. It's a little metal retangular box with probably 5 connectors on it. Hope this helps.


This is true for the S4/Sprint but not for the S1/2.... (and I think S3) they do not have a stabilizer for the gauges, the gauges are also not "damped" and swing/jump as the fuel gets sloshed about.
The cars still have a "voltage regulator" to control the output of the generator or (alternator if fitted.)
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PostPost by: Emma-Knight » Mon Dec 04, 2006 4:59 pm

It was a loose bullet, just half way in, behind the wiper motor (were rear loom plugs into main / dash loom. Cleaned a bit, fitted and works!

:wink: Anna
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