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Discussion Starter #1
Hi all,
My fuel gauge has stopped working I have taken wires from the sender and cleaned them up but it's still not working. Is there a way of checking if it's the sender, the wiring or the gauge?
Thanks in advance of all help and advice.
Patrick
Spider S3 with webbers.
 

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Disconnect the wire from the sender and ground it (connect it to earth). The gauge should read full. If it does then you most likely have a bad sender. If it does not it could be the gauge or the wiring. The gauges are pretty robust and don't usually fail.
 

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Ed is correct. Usual failure in the fuel gage system is the sender because it is electroMECHANICAL. All the rest is electrical for the most part. Electrics are less prone to failure than mechanicals.
 

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Discussion Starter #4
Which wire?

Thanks for the replies, I have looked and I have three wires, black which looks like earth and then two from sender. Violet and black/white. I have tried earthing both but no movement on gauge. I have taken sender out and float seems ok. Any other suggestion please?
 

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Unusual but it happens sometimes. Your troubleshooting indicates either an open wire from the sender to the fuel gauge (unlikely) or a faulty gauge, or a gauge not getting B+ power to the gauge.

BTW, the black wire to the sender is indeed a ground wire. the other 2 wires are;

1. B+ power to the in-tank fuel pump
2. fuel gauge sender wire to the fuel gauge

If you grounded the B+ power wire to the in-tank fuel pump, it should have drawn a spark and blown the fuse for that wire. At this point I would check ALL the fuses to make doubly sure that they are ALL good, then revisit the initial faulty fuel gauge problem.
 

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Violet is to the gauge. Black/white is to the low fuel warning light. With the ignition turned on you should be able to measure about 12 volts between either one and ground. If not you may have disconnected wires or a blown fuse.
 

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Discussion Starter #7
Hi Robert,
I'm not sure I have an in tank fuel pump. I took the sender out and all that was there was a piipe with a fuel filter on the end, my car has carbs does that make a difference? Just going out to check all fuses again but they were all ok earlier.
Thanks
Patrick
 

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Patrick,
Carbs make a big difference. On an 84 US model it will have Bosch FI and therefore should have an in-tank pump. On a model delivered with carbs, an in-tank pump is not necessary. When I offer an opinion, it is always based on US delivered models which are all I have any experience with.
 

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Discussion Starter #9
Hi Robert,
Thanks for the advice, it seems that almost all Alfa Spiders are unique whatever spec and country! Thinking of just changing the sender as I can't think it will be anything else.
Patrick.
 

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Hold on there, Patrick. If you cannot force a "full" gauge reading on the gauge with the sending unit wire at the tank artifically grounded, then you do not have a sender problem. Removing the sender wire and grounding it removes the sender from the equation and only leaves the wire and the gauge. If the gauge is getting B+ voltage to it - to work the gauge, then it has to the the wire open in the system, or a faulty gauge itself. If you can access the back side of the gauge and you artifically ground the side which connects to the sender, then the gauge will either register "full", or not. If you do this and the gauge reads full, then you have an open wire from the sender to the gauge, if the grounded gauge does not read full, then you have a bad gauge. Your next troubleshootinng steps are

1. verify that the B+ side of the fuel gauge is indeed getting B+ with the ignition key "on"
2. If you have B+ voltage to the gauge, then artifically ground the other contact on the gauge
3. the grounded gauge will do one of 2 things
1. continue to read nothing = bad gauge
2. read "full" = open wire from the sender to the gauge. Either find and repair the open, or re-lay a new sender wire from the sender to the other side of the gauge (non B+ side)
 

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On another note, how do you test the sender? Is it just a resistance reading when actuating the float? Do we have a ohm rating at full and empty tank?
 

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Most direct way to test the sender is to remove it and lay several layers of cloth over the opening in the fuel tank. Then with the key in "OFF" position, hook all the wires back up to the sender. Have another person sit in the drivers seat and turn the key to "on". You swing the float leaver through it's arc at the trunk. If the sender is OK, it will read between empty and full as you swing the float leaver. Don't unhook or hook up any electric wires around the opening in the tank unless the ignition Key is in the "off" position. Extreme fire hazard.
 

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For my 79 Spider Full = 0 ohms and empty = 168 ohms. Empty is the line on the gauge. It will read below zero with higher resistance. The circuit appears to be designed so that there is insufficient electrical energy applied to the sender to ignite gasoline vapors. The maximum current that it will draw is 90 mA. This is probably a federal regulation.
 

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Discussion Starter #14
Hi all,
Thanks for the advice so far. I have measured across the violet wire to earth and it reads zero, across the black/white about 2 (ingnition on). All fuses seem to be ok. Tried getting to back of gauge, took radio out but still can't get to it, does the gauge come off to the front or do I have to get around the back?
Will have a better look at the weekend.
Patrick
 

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Ground connection?

Our '85 US spider has a black wire connected at the fuel pickup/gauge. I found the hard way it grounds at the rear tail light. Perhaps the ground has come loose or contaminated?
 

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Poor or faulty ground wires are the most commmon source of electrical problems on Alfas. I wire brush or steel wool any ground I get the chance to on my Alfa. Then I put electrical grease on the ground point as well as the ring connector on the ground wire. I add new grounds where none existed before and treat all contact points as decribed above. I use stainless steel hardware and elastistop nuts to keep everything nice and tight forever. My moto is "you can have too little ground, but you can never have too much ground". The nice thing about adding additional grounds is that it is all nice safe ground. No danger of electrical problems by adding additional grounds.

My trunk and the under side of my front bumper is a mass of added ground wires. I don't have inop lights at the rear or the front of my Alfa any longer
 
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