I have a sending unit for my '86. I had to soak the insides of the lines with acetone and laquer thinner to unclog them.
I have it mostly free and the parts will come in this week...
I would like to know how to test the sending unit when its by itself.

I have an alternative 12V I can use to test.
I have an extra fuel level gauge I can use.
I have electrical test equipment. (multimeter, test light, small jumper wires, etc)

I figure if I can somehow connect it all together, I should be able to test all of this.
I just don't know where to start hooking wires up to.

A little help please? thanks!

I hope I am giving the appropriate answer. The fuel sending unit should indicate 90 ohms with the float lifted to the "full" position and zero ohms when resting at the "empty" position. If at any point the resistance goes to a value over 90 ohms, the gauge will read past full.

Charlie

As cptsnoopy has already posted, 90 ohms full 0 ohms empty. The idea is to move the float lever very slowly to make sure that the ohm readings do not jump. It should slowly reduced the ohm reading as you move from full to empty. It is always a good idea to clean the coils and contacts then inspect them for any cracks or gaps. The coils can be repaired with an extra fine soldering tip and some solder. If you have a gap, solid wire can be used and soldered in place.

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I just made a jumper harness that was about 8 feet long that would allow me to plug in the fuel sender/pump to the chassis harness while I held the sender in the driver seat (just pull the fuel pump fuse so it will not run). Then with the power on, you can see the reading on the dash and make the needed adjustements.

This quote is from my 4.9 swap thread:

quote Originally posted by josef644: Just checked the fuel gauge sending unit. Worked like a champ.: Empty: Full

Never did get it to '0' out. All you need is a meter on the OHMS scale. Put one end on the ground wire, and the other on the sending unit wire. You then can move the float up and down and watch the readings on the meter.

To test the gauge I purchased some 25 ohm resisters at Radio Shack Then you need to put around 100 ohms resistance, (4) between the sending unit feed and ground the other end. The gauge in the dash should respond to above the full mark. . Using two of the 25 ohm resisters, the readings should be just over 1/2 tank mark.

You will norice that the gauge moves very slow compared to the movement of the sending unit float arm

[This message has been edited by josef644 (edited 01-04-2011).]

I'm in the process of doing the larger fuel tank swap and decided to try and 'zero' the level gage in the process. My inital Ohm readings were something well over 100 - full and around 25 at empty. I took the resistor out of the sending unit and cleaned it using some Barkeeper's Friend (a copper cleaner for cooking utensils). I ended up with pretty close to 90 Ohms full and about 7 when empty (about what Josef shows in his pics).

There is also a little bit of adjustment with plastic piece that the resistor fits into. It is held on the sender by a couple small screws and there are two small springs that go between the resistor assembly and the main part of the sender. The screws weren't initially tightened down all the way which gave the resistor a little bit of cushion. This also increased the length of the arc struck by the wiper as it moved across the resistor. I found I needed to tighten these screws all the way down to get the best reading.

As for the wiring, you can look at the sender to figure out what each wire is for. Mine were: Black - ground, gray - fuel pump power, purple - 0 to 90 Ohms for level circuit.

Hope this helps.

Gary

For those not quite getting zero at empty. A fix for that was posted many moons ago by someone. It involved soldering the last couple of coil wires together on the end of the board that the wiper was on when the float was down. That worked for me.

Charlie