1984 Silverado Fuel Gauge Issue

[The1984Silver]

Hello everyone, My fuel gauge is not working and i would like to fix it due to the inconvenience it can cause  . So once before it stopped working and i replaced the gauge and that fixed it for awhile now its no longer working. The gauge will read 1/4 tank most of the time but sometimes it goes to empty. So the things i have done is:
-Took the gauge back out and test for a good ground which seams to be fine.
-Tested for 12 volts ignition signal when the ignition is On which i am receiving about 12.163 or something so that's fine
-Now i wasn't sure how to test the signal wire so this is where i need help figuring out if its the sending unit/wire or the gauge its self. But if i remember correctly its was 1 or so volt at the signal wire and with the ignition on i got 49 Ohm's and with the ignition off i got low Ohm's.

[Kimper]

I am having the same issue with 76. I hope someone can help..

[Irish_Alley]

see if this helps

[Irish_Alley]

from the link above

TEST PROCEDURE - GAUGES
Using an ohmmeter set to the appropriate scale, "zero" the ohmmeter if the meter requires it.  Then, while referring to the subsequent gauge-specific charts, with the ohmmeter connected to the tester leads, adjust the tester to the stated resistance for testing the 'Low' index line of the particular gauge and year vehicle.

Once the tester is adjusted, substitute it for the gauge sending unit by unplugging the wiring harness from the sender, connecting one lead of the tester to the sender wire, and the second lead of the tester to a verified, good ground.  Turn the ignition ON.  The gauge needle should point to the lowest reading (leftmost index line) on the gauge face.

Similarly test the 'Mid-range' and 'High' index lines of the gauge by systematically resetting the tester resistance according to the appropriate chart.
 
A correctly reading gauge indicates there are no problems with the gauge or its wiring, limiting any faults to the respective sending unit.

An incorrectly reading gauge calls for further testing and verification of 12-volt ignition power, grounds, connections, and associated wiring.

TEST PROCEDURE - SENDING UNITS

The subsequent charts provide precise sender resistance values for three specific gauge readings (Low, Medium, and High), hence, can be used to estimate sender resistance when actual physical parameters are known (e.g., engine temperature that is verified with a thermometer, actual fuel tank level, engine oil pressure that is verified with a manual gauge, etc).  Therefore, a sending unit’s resistance can be measured and “subjectively” compared to its interpolated value between ‘Low,’ ‘Medium’ and ‘High,’ based on the charts and the observable/verifiable physical conditions that actually exist on the vehicle.


FUEL LEVEL GAUGE PARAMETERS

For Truck Years:  1967 - 1990

The Fuel Gauge Needle Should Point to:
Left Line (Empty) when sender resistance = ~1 Ω
Middle Line (Half) when sender resistance = 44 Ω
Right Line (Full) when sender resistance = 88 Ω

[Gusgusa1]

Thank you my RH tank reads 3/4 when full.

[Gusgusa1]

Works

[The1984Silver]

Alright so i get 12 volts at the gauge, it has a good ground, but it reads 104 ohms when i have around a half tank or so at the sending wire. Problem is my stock gauge reads 1/4 and the other gauge i got reads a little past full. Only problem is i thought the problem was fixed because it read full on the 2nd gauge and i knew the tank was full of gas but when i put it all back together it went full empty so now im at a loss for ideas.

[The1984Silver]

Update: So more weird issues sometimes i get 91-94 ohms other times 104-130ohms but the weird thing is both my gauges read just over 1/4 even though their getting the 91-130 ohms i thought at 90ohms the gauge should read full. I'm now at a true loss for what this issue is. Im thinking the sending unit is bad since i get a reading as high as 130ohms but the two gauges reading 1/4 with 91-130ohms pumping though it makes me wonder if both the gauges are bad or whats happening there.

[Irish_Alley]

im going to let BD or hatzie take over. im still learning off them lol

[Kimper]

Run a jumper wire directly from the stud on the sending unit to the gauge and one from the ground on the sending unit to the battery ground, then check the gauge and see if your getting a good reading or not. If that doesnt help I would pull the sending unit out and ohm it out at the sending unit itself and move the float up and down while watching your volt meter. It should read around 0 at the empty side and around 90 in the full . That way you know if your wiring is bad in the truck or not or if it's your sending unit. I just did this and mine and it was reading 109 on full and 16 on empty which ='s a bad sending unit.

[The1984Silver]

I jumped the sending wire to the gauge and got same reading just over 1/4. Whats a way to test the resistor on the gauge because i think both gauges are bad. Even though i know the 91-130 ohms is wrong from the sending unit, i don't see how the gauges read just over 1/4 with that many ohms it should be read past full correct? I'm going to pull the tank out when i wake up and report the results i get.

[Kimper]

Yes yes are correct, andything over 90 ohms should be past full. sounds like a a bad gauge to me. Did you have the ground jumpers as well to the battery just to eliminate that as well??

[The1984Silver]

Yes i did check everything to make sure it had a good ground so i should be okay their. But guess ill be buying my 3rd gas gauge tomorrow...

[Irish_Alley]

Testing for a inoperative fuel gauge sending unit


Fuel System Schematics (and fuel gauge troubleshooting)

[bd]

You are making this way more difficult than it needs to be. 

...Something i thought i would mention is that if the gauge is installed and i push on it sometimes it will go to full and then when i push in another spot it will go back to a quarter....

This ^^^^ is an indication of an intermittent connection between the gauge and the flexible printed circuit board (PCB) on the back of the instrument cluster.  Typically, this is caused by accumulated dust and oxidation between the PCB and the three silver spring clips that protrude through the back of the cluster housing to engage the pins on the back of the fuel gauge; and/or a loss of spring tension between the clips and the gauge. 

To correct electrical continuity problems between the PCB and the gauge, remove the cluster from the vehicle.  Remove the fuel gauge from the cluster.  Carefully remove the spring clips protruding through the back of the cluster housing being careful not to tear or damage the PCB.  Using crocus cloth or a Pink Pearl eraser, gently clean the copper foil where the spring clips for the gauge push through the PCB and snap into the back of the cluster.  Be very careful while cleaning the PCB to avoid peeling the copper foil loose from its plastic sheet.  Next, polish the little contact arms of the clips.  Using a pair of needle nose pliers, tweak the spring clips ever so slightly to increase the tension between the spring clips, the PCB and the gauge pins when installed.  Smear a sparing amount of antioxidant paste or dielectric grease on the copper foil where it contacts the spring clips and reinstall the clips through the back of the housing so they snap and lock into place, making a firm connection against the PCB.  Check the nuts securing the ceramic resistor to the back of the gauge to ensure they are snug, then reinstall the gauge, set the cluster into place in the dash, and reconnect the harness to the cluster.  But, don't completely reassemble the dash yet...

Yes i did check everything to make sure it had a good ground so i should be okay their. So i need a new gauge and sending unit then? I don't understand how 2 gauges and the sending unit can go bad. Ill put a new sending unit in and still have a wrong reading because the gauge seams like i cant win. Guess ill be buying my 3rd gas gauge tomorrow...

• With the factory fuel gauge installed and hooked up, disconnect the signal wire from the fuel tank sending unit.  With ignition switched on the fuel gauge should climb way past full to about the 3:00 o'clock position.  Does it?
  
  
• Ground the signal wire leading to the gauge and with the ignition on the fuel gauge should drop to empty.  Does it?
  
  
• Connect a 45-ohm, 1/2-watt resistor (procured locally from Radio Shack or similar electronics supply) between the sender wire leading up to the fuel gauge and a good, clean, bare metal ground.  With the ignition switched on the fuel gauge should indicate 1/2 tank.  Does it?

Report your progress and findings then we'll go to the next step.  Incidentally, are you using a digital or analog meter?