Fuel gauge operation.

[Keith Scarfe]

My fuel gauge seems to have packed up. It was always a bit strange in operation - normally rammed onto end stop (full) until the tank is less than half full then I have to tap it and the needle jumps down. It then measures the level for the last 1/2 or so of a tank. As the car moves and the fuel sloshes around the needle follows the level (too quickly/accurately) and usually bangs into the end stop again requiring a tap to release it. Does everyone else?s behave like this or is it just mine?
I need to check out what is up with it so I was going to first take out the gauge and bench test it with a resistor bank. Does anyone have a sender they can measure for me or do you know what the resistance is when empty, 1/4, 1/2, 3/4, full etc? Does it go open/closed circuit at either end? Are they all the same on different models - Mine is an S3 with wiring more like an S1/2. It is far more of a job to take the sender out (when the tank is full) so I thought I would check out the gauge and wiring before doing this.
Thanks.
Keith.
p.s. I have just swapped from pos to neg earth. I can't remember for sure but I think this had packed up before doing this and I can?t imagine it would effect the fuel gauge anyway but it might I guess. Do I have to swap the wires on the back of the gauge?

[types26/36]

Both my S2 and S3 gauges dance around, sometimes I have to tap them to move the needle from full/empty. I think you will find that your S3 does not have a stabilizer (S1 & S2?s don't have them) and I have never seen an S3 with one.
The S4?s sender and gauge are not the same as the S1/2/3?s which is no longer available although the S4 is still available but as I remember it works the opposite way round with different resistance's. I think you would have to change both the gauge and sender if fitting an S4 type.
I think I have the resistance's written down somewhere and will have a look if no one else knows.
I repaired the sender on my S3, the winding was broken and I took out one loop and soldered it, I think it has a dead spot somewhere but the gauge readings don't worry me as I carry a graduated piece of wood to dip the tank
....I never changed the gauge wiring when I converted to negative earth.

[ardee_selby]

The SJS site differentiates between the S4 & Sprint only "sender" and a "tank unit" which, presumably, is a replacement for the OEM pattern used on the S1, S2, S3?

Anyone fitted one?

Cheers - Richard

[Tonyw]

Richard,

I did but you need to also change the guage to an S4 Sprint type to get the sender to work.

Tonyw

[elanner]

elan-f15/fuel-level-sender-unit-query-t21391.html provides resistance numbers for senders.
http://www.mgb-stuff.org.uk/fuel.htm seems to have some helpful information.

Nick

[types26/36]

Here is what I have down in my notes for the values (cant guarantee they are correct though)
S2 .............. FULL = 90 ohms .........EMPTY = 0 ohms
S4/SPRINT.. FULL = 20 ohms .......EMPTY = 262 ohms

[Keith Scarfe]

Thanks all for your help. Here is my intermediate report back as I have done a bench test on the gauge, but not fitted it back to the car yet.
Initially it was behaving just as when on the car which was good to see (good that the bench test replicates what is seen on the car). Any resistance greater than a couple of ohms sent the needle to the full end stop.
I found some interesting information here: http://mgaguru.com/mgtech/electric/fg_06.htm
Since my S3 type gauge is a moving coil instrument rather than a resistive bi-metallic type one, you calibrate it by undoing and sliding the two screws on the back. This moves the coils inside (I think) to make them act more or less on the needle movement. I did this and set it up nicely from both mine and Brian?s resistance values. 0-90 ohms as Brian suggested. Currently my tank is about 1/2-3/4 full and measures 60 ohms so that seems right. It is quite fiddly adjusting these. One effects how it behaves at low resistance and the other at high. So if one is min and one max the measurement is really non linear. I set them to about the same and got the measurements to show about right then set the min one to get empty at 0 ohms, then fiddled more to get it just right at all values. When loosening and tightening the screws it all changes so this adds to the fun.
I will now have to fit is back to the car and see if it is good now. I am sure I will need to measure my own sender as the level changes and maybe fine tune it further. I will report back with some final results.
Regards.
Keith.

[sveris]

While fabricating aluminum alloy reproductions of the Elan gas tanks, I learned the following:

S1, S2, and S3 models used mostly the 0 Empty to 90 ohms Full sending units.
S4 and Sprint models also used the 6 ohms Empty to 77 ohms Full sending units [both OEM and the VDO drop-in, tube type sending units had this curve; I had one of each in my hands last year and the measured readings were identical.]

I also encountered a 253 ohms Empty to 25 ohms Full OEM sender and OEM S4 Elan fuel gauge in a friend's car in California. Sounds to me like Colin might have been using whatever was in the bin on occasion.

HTH.

Steve in Ohio