Talk Morgan Forums Morgan Sports Cars Morgan Three Wheeler & Super 3 Fuel gauge sender/rack

That said, I do take on board that yours failed not long after a fuel runout. I suspect they are just a weak unit!

Need to take a dead pump apart. Has anyone got one?

Been experimenting with a range of shunt resistors wired directly across the terminals of my 280mm fuel sender.

Athough my calculations, based on the data Charles kindly provided, suggested a higher value would better suit, settled on a 750 ohm one.

Have now run two full tankfuls in testing with this value. With a full tank (three shut-off clicks) I see 100% reading for 20 to 30 miles before reading begins to drop, with 210 - 230 miles of driving before 0% appears and stays there. At this point a refill takes a little over 30 litres.

As before the reading jumps up and down during driving, but although not optimal, I now find I have a usable gauge for a 200+ mile journey without spending miles driving with the gauge on 0%.

YMMV but imagine others could benefit from the quick and simple mod. BTW I used 0.5 watt resistors in testing as the current through sender circuit is minimal.

Richard... I'm an electronics moron. Therefore, I'd welcome a picture. If I go to my local American Electronics store, and ask for a 750 ohm shunt resistor, will they understand? Is a shunt resistor different than a resistor? Wired right across the + and - terminals?

Hi Ken. No its just a regular resistor, the term shunt just refers to the manner in which it is wired in parallel with the sender.

I bought mine from Maplins a chain electronics outlet in the UK. It's a metal film 0.6 watt with 750 ohms being a common value, costing just a few pence. Will post a picture when I can but just used crimp connectors with suitable eye tags. One under the central connection the other on the adjacent screw where the loom ground attaches.

👍🏻

Richard, are you using the 250mm original sender or the 280mm one? Do you have the Maplins part number for the resistor you used, it would be handy? Also a photo of the installation sometime please. Sounds like a easy way of getting a bit more accuracy into the fuel contents system. With the 280mm sender I get 100% for a long time after filling, probably about 80 miles, then it drops to 0% after about 200 miles from filling.

Just left the electronics store. The .6 watt seems to be made of unobtainium but he said that wasn't crucial. I have a 750 ohm 2% HW175 and will be installing it shortly. Then a fill up and observation! I'll report back.

Yes using the 280mm sender as it wouldn't be worth electrically tweaking the shorter one.

If yours works as described there probably wouldn't be much improvment with the resistor tweak, but you could always experiment

With hindsight the best way of attaching the resistor would be soldering to the spare brass tags supplied with the sender
to fit under the terminal screws. Sadly I threw mine away

Good luck, resistor sounds fine.

BTW suggest having a good long test running a full tankful through the engine before forming any opinions. The software that drives the fuel display appears to have some weird damping algorithms. When I first checked with ignition on but before starting engine, I watched the display falling steadily for several seconds. All seems to settle down after a few miles driving though.

Both before and after mod I often noticed display level drop and then rise again as much as 15% a few miles later. By the same token a particular display percentage can get pegged for as much as 20 miles before dropping.