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My fuel gauge recently started acting out. More often than not, it will start out not registering at all and then, suddenly, come to life (or not) after driving for a little bit. Once it comes to life, it stays there until I stop and turn the ignition off. The problem then repeats itself. (BTW, the low fuel warning light works regardless of the gauge's operation).

I tested the following per a member's old post:

Just to check the guage: ground the violet (purple) wire on the sender in the tank - your guage should go to max ...does it?
you can also check the low fuel warning light operates whilst you are in there, by grounding the black/white wire....warning light should light.
I would also check the ground for the tank sender (supplied, obviously, by the black wire on sender!)....run a separate wire from a good known ground (-ve pole of the battery for instance) to the sender unit itself. I do not know if that would effect the guage reading only half, but no harm to test it in any case

EDIT: sorry, forgot, key (ignition) on!


Grounding the violet wire sent the gauge to max. The low fuel warning light works when grounding the black/white wire. Running another ground wire to the sender had no effect.

Any thoughts?

Thanks in advance.

Ken
 

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sounds like some old post of mine;)

have you had the in-tank pump out recently...? if so was it put back in right orientation?
(the ground tab faces the spare wheel well, iirc)

sounds like the sender in the tank is acting up...maybe the plastic float is holed?
I'd pull it and see what it looks like....not sure if you can open the sender bit and clean the slide on these later parts (a little copper slide runs up and down a fine wire winding)

but you might be able to at least bench test it with an ohm meter.
 

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I had a gauge from an S2 Spider on the bench and 5 ohms made it read full scale and 90 ohms made it read empty. I expect that your gauge has a similar range.
 

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Discussion Starter #4
sounds like some old post of mine;)

have you had the in-tank pump out recently...? if so was it put back in right orientation?
(the ground tab faces the spare wheel well, iirc)

sounds like the sender in the tank is acting up...maybe the plastic float is holed?
I'd pull it and see what it looks like....not sure if you can open the sender bit and clean the slide on these later parts (a little copper slide runs up and down a fine wire winding)

but you might be able to at least bench test it with an ohm meter.
Yes, it was you. You recognize your own prose. I haven’t had it out recently but i will take it out now for examination. Thanks.
 

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Your sender is worn out and the wiring locations and grounds need to be checked. The gauge is always the suspect but never the perpetrator. If the reserve light is on all the time, the sender is probably wired backwards.
 

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Discussion Starter #6
Your sender is worn out and the wiring locations and grounds need to be checked. The gauge is always the suspect but never the perpetrator. If the reserve light is on all the time, the sender is probably wired backwards.
To clarify what I meant by "...the low fuel warning light works regardless of the gauge's operation", I meant that it's working correctly and independently of the gauge.
 

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I had a gauge from an S2 Spider on the bench and 5 ohms made it read full scale and 90 ohms made it read empty. I expect that your gauge has a similar range.
perhaps a dumb question, but... does that mean that a standard Jaeger fuel gauge responds to a resistance range of 5-90 ohms to be accurate at E and F, respectively? So, if the range of a new sender is 5-300 ohms, that means that at 90 ohms the gauge will show Empty but the float will be in a position that corresponds to, say, half-full, yes? If that’s the case, then is it correct to slightly bend the tang on the sender to tweak the upper resistance reading to be closer to 90 ohms?

i guess what I’m asking is... if a stock Jaeger gauge responds to a range of 0-90 ohms, then the gauge will be accurate. How can I confirm that 0-90 is the range that the gauge responds to...?
 

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Just curious... Why a discussion of a Jaguar sender? New Alfa senders are reasonably priced.

But to your question...

A sender that has a different “span” than is intended to be used with a certain gauge, you are not likely to get an accurate E, and F, and/or the response in between will not correctly indicate how much is in the tank.

It is possible to create correcting circuitry to match a sender to a mismatched gauge, but this brings us back to why not just buy the right sender?
 

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86 Veloce
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Jaeger, not Jaguar like the car.
 

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I am getting blind and hard of listening. Oh well...
 

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86 Veloce
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That's ok! Easy to make that mistake. The Jaeger senders for our Spiders are readily available but I hear the bracket is hard to come by.....
 

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There are only a few sender calibrations, and 90-5 ohm seems to be the least common. Pre 1967 Smiths were 0-90 then changed to the more common 240-33. VDO used 180-10 on German cars. The only trace I've found to another application using 90-5 would be early VW buses (back when the Beetle didn't have a gage).

Anyway the Alfa senders are available from the usual sources.
 

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There are only a few sender calibrations, and 90-5 ohm seems to be the least common. Pre 1967 Smiths were 0-90 then changed to the more common 240-33. VDO used 180-10 on German cars. The only trace I've found to another application using 90-5 would be early VW buses (back when the Beetle didn't have a gage).

Anyway the Alfa senders are available from the usual sources.
I'm guessing but the size of the rheostat and the radius (arc) of the sweep and the depth of the tank all have something to do with the resistance requied to feed the gauge.
 

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86 Veloce
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I can be a little Neandertal at times. I just took mine out and bent it until it read close I really only care about 1/2 and below being accurate....
 

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Who is “Donald”?
 
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