Info for tomorrow when i'm buggering around with the fuel tank sender.
75ohm ety - 10 ohm full
REMOVE THE SINGLE WIRE FROM THE CENTRE OF THE SENDER UNIT ON THE TANK, AND PUT IT TO EARTH (METAL WORK OF THE TANK OR BODY WORK), YOU MAY NEED TO STICK A BIT OF WIRE INTO THE THE FEMALE CONNECTION IF THE COPPER PART IS RETRACTED INTO THE CONNECTOR SLEEVE.
SWITCH ON THE IGNITION, AND THE GUAGE SHOULD GO ALL THE WAY AND OVER THE FULL TANK RANGE, DON'T LEAVE THE IGNITION SWITCH ON FOR MUCH LONGER THAN YOU NEED TO PROVE THIS TEST, IF THE GUAGE MOVES ALL THE WAY THEN THE GUAGE IS OK.
To test sender unit -:
USE A MULTIMETER SET TO OHM'S (RESISTANCE), AND WITH ONE PROBE ON THE MALE CONNECTION OF THE SENDER UNIT AND THE OTHER PROBE TO EARTH OF TANK/CAR BODY YOU SHOULD GET A RESISTANCE READING, IF THE TANK WAS SAY HALF FULL, IF SOMEONE WAS TO SHAKE THE CAR FROM SIDE TO SIDE THE RESISTANCE READING SHOULD FOLLOW AND LOWER/RAISE, THIS WOULD THEN AT LEAST SHOW THAT THE SENDER WAS NOT OPEN CIRCUIT.
Step 1 - Removing the sender
1. Drain the fuel tank. I'm sure I don't need to tell you the tank needs to be empty before removing the sender
I was also removing the tank to clean and paint which made the rest of the process a little easier.
2. Disconnect the wiring. If yours is anything like mine it will be virtually impossible to remove the connections from the sender. Rather than doing any irreparable damage, I simply clipped the wires as close the sender as possible.
3. Remove the sender. This should be a simple case of unscrewing the sender from the tank. The best way I found to do this was to make a tool from a length of 1"x1" wood with 2 bolts through it positioned so that they fit into two of the notches in the sender unit. With this it becomes much easier to unscrew the unit from the tank (don't get rid of the tool yet though, you'll want it to screw the sender back into the tank later). Failing this though, you can just knock the sender unit round with a hammer cushioning the blow with a block of wood.
Step 2 - Cleaning
1. Spray the sender generously with marine clean and go and have a beer while you wait for it to do it's thing
2. give it a good rinse pat dry with a cloth.
3. remove the old gasket and wiring connectors. There is no real magic trick to this, I just carefully twisted at them with the pliers until they came loose. If they won't budge, leave them where they are, you may have more luck after the next stage.
4. give the main body of the sender a quick scrub with the wire brush to remove any loose flaky crap being careful on the inside around the wiring.
5. prop the sender so the main body is as flat as possible in an old ice-cream or take away tub and fill the tub with the rust remover until it covers the body but without coming into contact with the blue wire that wraps around the tube (I don't think it actually matters but since it's a mild acid I figured it would be better to be safe).
6. go to the pub, you're done for today, you need to leave it like this for 12-24 hrs for the rust remover to work it's magic.
Step 3 - Cleaning cont.
1. remove the sender from the rust removed and give it another scrub with the wire brush. If not previously removed, you should be able to pull the wiring connectors off now.
2. repeat the soak and scrub until you are happy with it.
3. clean up the wiring terminals with the wire wool until bright and shiny
Step 4 - Testing
Time to see how we're getting on.
Note: This part is easier if you have a multi-meter with crocodile clips on the probes but it's not essential.
With the body of the sender held gently in a vice (or by a friend or taped to something) and the multi-meter probes clipped to the wiring terminals you should be able to get a resistance reading that varies as you move the float arm from one end of it's sweep to the other. If you are getting a clean and steadily increasing reading as you move the float from one end to the other at this stage, you probably don't need to muck about with it any further and can skip straight to reassembly. If however, like me, you get readings that jump about and portions of the sweep which give no reading you'll need to take a look at the rheostat and clean this up too (see step 5).
Step 5 - Fixing dodgy readings
1. dismantling the rheostat housing. The top of the housing is held on with a number of tabs that are bent down over it, simply straighten these and the top should come free (be careful though as this includes a bunch of small parts including a spring).
2. once opened up attached to one side is the rheostat (a red block with a series of parallel metal stripes across it. To give this a clean just give it a gentle scrub with the fine sandpaper.
3. the corresponding part in the rheostat is the contact tab attached to the float arm. This is basically just a blob of solder on the end of a sprung arm that pushes against the red block, again this just needs a quick clean up with the sandpaper to make it bright and shiny and to gently bend the sprung arm to make it put a little more pressure on the contact point.
4. reassembly should be simply the case of putting it all back where it came from and bending the lock tabs back over the top of the housing. To save bening the tabs too much though, it's worth checking it's worked by repeating the test in step 4 whilst holding the unit together by hand or with some tape.
Step 6 - Reassembly
Once you're happy that it's all working as it should, it's simply a case of giving it a quick paint (remembering you only need to paint the main body and not to cover the wiring terminals) and reassembling
1. once painted I ran a small bead of Hylomar round the gasket contact area then pressed the new gasket into it.
2. once fitted I then applied a second bead of Hylomar onto the other side of the gasket to seal against the tank when reassembled. Technically this shouldn't be necessary as the gasket alone should be sufficient to make a seal, but I figured it can't hurt.
3. refitting the sender is the exact reverse of removal, turning it (with you're special tool if you made one) through 90 deg. to lock it in place.
4. reconnect you're wiring (using some new crimp connectors if necessary) and fill the tank (checking for leaks of course)