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TOPIC: Inop fuel gauge-fuel sending unit

Inop fuel gauge-fuel sending unit 17 Oct 2010 19:56 #1689


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When a fuel gauge starts to read empty all the time, the most likely reason is due to a stuck/inoperative fuel sending unit.

The unit is located in the hatch area, under the carpet on the passenger side. Typically covered by a plastic, round cover, that is black. Pop that off and you will see the top of the gas tank, the sending unit that has one hose and a wire connector attached.

To remove the sending unit is very simple, take the hose off (one hose clamp) and gently pull the hose off the unit. By now most of our hoses are close to crap, so be careful. I usually take the clamp off the hose, and then work the hose off the nipple, not putting any bends in the hose.

Pull the wire connector off. From the connector you can actually test and see if it is in fact the sending unit, sometimes it is an actual cluster issue, but chances are it won't be. Take a jumper wire, with the ignition key on, and jump 2 of the three connectors. I don't remember the sequence, but it really does not matter. As you are jumpering, you will see the gas gauge jump to full. This will tell you that the gauge works, and the sending unit does not.

* do not remove the sending unit if you have a full tank, you will end up with over flow, do it with 1/2 tank or less.*

Removal of the sending unit. For the guys with just a basic tool set, take a large cresent wrench, one that will open wide enough to get to both sides of the black/ribbed plastic nut, and unscrew it. Once you get to a high point on the large nut, you will need to unseat the sender either by lifting or twisting, once it is unseated you can pull the sender up a bit and then remove the large nut.

Pull the sender out, above the gas tank level and tip is sideways as you lift it out, you will see the fuel empty from the sending unit. Once that is drained a bit go ahead and pull it out and get it out of the car.

At this point, you can either install a new unit or try to refurbish the old unit yourself.

Pictures to follow with cleaning one up.

Once you have the old unit out, at the bottom there is a 5mm nut that needs to come off, pull it and the washer, then pull the funnel off the unit. Under that you will see another 5mm nut that does not have a washer. Take it out and then gently pry the black plastic cover off the bottom of the sensor.

At this point, the cylinder that holds everything together is free to come off, slide it off gently and you will see why they fail. Massive amount of varnish and corrosion along the return tube, the slider for the float, and the electrical connections. On the one in the pictures, I sprayed a bit of brake clean on it, then took a small file and removed all of the corrosion I could. Cleaned up everything that looked varnished and put it all back together.

You will notice that there are three wires that guide the float, do not kink those, these are what helps give the reading to the gauge. Do your best and make sure the float moves smoothly from top to bottom.

The pictures below are from a 1980 Euro that sat in storage from 2001 until today.

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Inop fuel gauge-fuel sending unit 18 Oct 2010 08:11 #1694


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How familiar? Seems like just yesterday I had to take these very same steps to free my sending unit on my '84. Pretty easy job. Good write-up, Sean. Excellent addition to the "Technical Tips" section. I suspect many owners may not realize that they're inoperable fuel gauge could be fixed this easily.

A tip of my own to compliment Sean's advice: If you're suspicious of an electrical problem with the fuel gauge like a broken wire or something, turn your key to the "on" position. Leave it there. There are two plug connectors at the bottom of the cluster. One on each side of the wheel exactly parallel to each other. One for the right side gauges and one for the left side gauges. CAREFULLY remove the harness connector for the left side instruments with the ignition left on. If the fuel gauge now reads full, then you have eliminated a fault with the wiring and the gauge itself. The amperage gauge should also shoot to 16V or slightly higher when this is done.
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Inop fuel gauge-fuel sending unit 05 Jan 2012 10:27 #7627


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Has anyone repair the plastic electrical circuit board? I have sent mine out to be overhauld twice, once because tactometer did not work and voltage meter needs the engines revs increased to kick-in. Sent out instrument cluster for repairs, cluster came back, re-installed, temperature gauge did not work and volt meter still does the same thing. I am sure alternator is the problem not the gauge. Return instrument cluster, short turn arround time. Fuel gauge does not work this time arround but low warning light does. Plastic circuit board does seemed creased. The circuit boards are NLA and I have not seen a used one. Car is 1984 automatic. The fuel and temperature gauges are next to each other and seem to get there power from the same copper "wire".
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Inop fuel gauge-fuel sending unit 01 Aug 2017 18:27 #19931


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So question. I am new owner of a 1980 Porsche 928 and basically all my gauges aren't working. My fuel gauge has stayed on full since I replaced the fuel sending unit brand new. I thought it was working cause it was at 3/4 and then I filled the car completely full and now it reads above full but isn't moving. What steps should I take to figure this out if anyone could help please?!?!?
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