Managed to get another hour on this yesterday and had a look inside the tank at the O/S (pump) sender unit. Didn't get too far as I needed the car for work last night and was worried I might break something ! Will have more time next week though.
Anyway, have uploaded some pics to show the progress so far and hopefully assist others if they want to test their own systems....
a) This was the initial testing of the fuel gauge using a selection of fixed resistors, each of a known value within the normal sender range, to determine if the needle was showing the correct amount. The normal range is about 10 to 360 ohms (I believe, from measuring a couple of old units), so a resistor of around 180 ohms should place the needle about half way up the gauge. I used five different resistors to get the gauge to show 1/8, 1/4, half, 3/4 and full:
b) I then made up a simple link lead to allow me to run the car for a few days with the senders disconnected but the fuel pump attached. I could substitute the fixed resistors once again and see if there was any abnormal behaviour in everyday use. Please remember this was only a temporary thing....it looks a bit bodged !!:
c) I then tried a variable resistor in place of the fixed ones, to move the gauge with everything running. Unfortunately, I forgot to take a pic, but just used a basic 500 ohm potentiometer. With the ignition on, the gauge moved exactly as expected, as it had with the fixed resistors.
d) Then yesterday, I had a close look at the pump side rheostat track. Quite grubby, so a quick wipe with a cotton bud to clean it up temporarily. The tracks do look quite tarnished. Next week I'll have a better go and use some contact cleaner, possibly removing both senders from the tank:
e) Lastly, I had a close look down inside the connector, as corrosion here would give increased resistance, but they actually look very clean (not sure if it'll show up in the image):
It does look more likely to be the rheostats, will dig deeper next week. Does anyone know if the metal tracks can be replaced, or are new boards available without having to buy the whole pump/filter units ??
