Fuel Gauge Trouble Shooting Help Needed!!

[kevindahle]

Alright here is the deal, the gauge on my 73 Duster hasn't worked in a while, so I assumed the sender was bad, got a new one, installed it and put gas in it 6-7 gal. and it still didn't read anything. so first i checked the ground to the sender by hose clamping a wire to the sending unit and directly frame grounding it. Still nothing, so I made a jumper wire from the ground to the sending unit wire and turned the key on and it shot up tp full, I then checked the new installed sending unit with a ohm meter and got a reading of 44ohms. but nothing at the gauge. what could I check next??

 

[kevindahle]

Also I did bench test the new sending unit with a ohm meter and it checked out good.

 

[BillGrissom]

Does your temperature gage in the dash read wrong also? If so, both fuel and temp gages rely on the 5 V regulator in the dash, which commonly goes bad. In 1973, it is a rectangular shiny metal can that plugs into the dash circuit board (rear). But if you have rally gages (tachometer), I think it was still buried within the fuel gage in 1973. Either way, best to replace w/ an electronic Vreg ($30 ebay, search "voltage limiter").

Otherwise, you need to tap into the "body harness" behind the driver's kick panel and measure the sender signal (resistance) there and use simulator resistors (Radio Shack) to test the gage. Need a lot of alligator jumper wires.

 

[67Dart273]

44 ohms should read SOMETHING on the gauge. It might just be a bad connection in the wire end. As Bill said, you can dig into the harness at the kick panel connector

the readings are:

L = 73.7 Ohms (empty)
M = 23.0 Ohms (1/2)
H = 10.2 Ohms (full)

so I would think 44 ohms would read 1/4 or so.

As bill said, pick up some resistors at radio shack, at least 1/2 watt. If you buy 4 100 ohm and wire them all in parallel, that will give you about 1/2 scale

All gauges are the same, so you can check the accuracy of your temp gauge at the same time.

 

[kevindahle]

I will check the connection behind the kick panel that should be ez, I didn't know that the temp gauge and the fuel gauge rely on the same regulator, I don't think that is working either, its been years since the car has been in service about 10 years ago the auto trans started slipping that lead into a 4-speed swap that lead into a floor replacement that lead into .......LOL, last I remember the fuel gauge was working but inacurate. well you guys gave me some great advise so I'll see if I can get to the bottom of this. Thanks

 

[67Dart273]

If neither gauge works it could be several things, including but not limited to

the connector to the cluster

corrosion/ loose connections right at the gauge studs

bad / poor gauge regulator, or bad connections in the socket it fits

(DO you have a rally cluster?)

Of course the gauges themselves

And of course sender wire problems. Don't forget the temp sender wire goes through the bulkhead connector, which could be a bad connection.

 

[wjajr]

Still nothing, so I made a jumper wire from the ground to the sending unit wire and turned the key on and it shot up tp full,

Now you know the wire from tank to gage is conducting properly. You have narrowed the problem to two possibilities: first how well the rubber plug at end of wire at tank connects to sending unit’s terminal; and secondly is the sending unit grounded properly. If I were a betting man I would say that the sending unit is not grounded well enough, and is adding additional electrical resistance to this circuit. If total resistance of sending unit and ground path added together is greater than 73 ohms the gage reads empty. This also correlates with previous low fuel gage indication when full.


Metal fuel line is factory path to ground for this circuit; this path can become corrupted from corrosion at each of fuel line’s brackets, and tube’s corroded surface. Be sure to scrape fuel line’s surface to clean metal when bridging rubber coupling between sending unit and fuel line. You may have to run a new #16 gage ground strap from sending unit’s fuel tube to frame of car for a voltage drop free ground.