Gas Guage Prob's

[79Betty]

I have a 78/79 k10, A 1/2 ton lwb. I had to buy a new gas tank and also got a new sending unit, got it in n wired up good... But my gas guage won't go below a half a tank. This is my 2nd guage as my first one wouldn't sit still, it just bounced from E to F every time i hit a bump. Is my 2nd guage bad as well? I'm going to run after market guages in my bezel but until then i need a good one. Do any aftermarket's (prefferbly equies so it matches) make a guage that will work woth our sending units? Thanks
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[frog210]

all the wires making good contact?
clean maybe the terminals where the gauge prongs go into
maybe check behing your cluster for a lose ground or loose sender wire
my gauge bounces too when i hit a bump, when my tank is full it dosent bounce but once it has a few gallons out, the gas sloshes and gives a false reading
you can check your gauge with 2 C batterys

[78 Big10 454]

I had the same problem with my square. I tracked down the wiring and found a spot where the insulation had worn off and would ground to the frame whenever I hit a bump or rough road. My problem was where the wire ran along the inside of the frame, right below the passenger side door. Electrical tape can be a life saver.

[hatzie]

Bouncing is normal in an air core meter. It can be mitigated somewhat with an injection of some special silicone damping gel. Gauge repair guys can do this for you pretty quick.

Not dropping below 1/2 tank indicates increased resistance somewhere in the circuit. Is the ground wire from the sender to the frame making good contact?

You can bench test a fuel gauge with a charged 12v battery, 4 alligator clip test leads, and a couple 1/2W resistors (100ohm and 50ohm 90 & 45 would be better but 100 & 50 are close enough).

It's worth noting that the resistors can get VERY HOT so be careful of where you place them... not on the kitchen table or those greasy rags.

If your gauge passes these tests it's not the problem.

• Lay the gauge face down with the 1/2 tank position pointing straight toward you and the indicator lamp window straight away from you.
  
• There are 3 studs on the back of the canister arranged at the points of a triangle.
  
• The (-) GND stud is at the apex of the triangle away from you and closest to the indicator light window. Clip your battery (-) to this stud.
  
• The (+) IGN stud is on the Left hand side of the gauge closest to you. Clip your battery (+) to this stud.
  
• With just the + & - studs hooked up the needle should go almost horizontal @ 3:00 on the face past full.
  
• The Sender stud is on the Right Hand side of the gauge closest to you. Hook a jumper from the ground to the sender stud. The gauge should drop to Empty.
  
• Remove the ground to sender jumper.
  
• Clip the 50ohm resistor between two test leads. Hook the loose ends of this from the ground stud to the sender stud. This should put the needle at just over 1/2.
  
• Un-clip the battery (+) lead and wait till the resistor cools enough to handle.
  
• Swap the 50 ohm to the 100 ohm resistor and hook the battry (+) lead back up. This should put the needle past Full but not 3:00.
  

[motornut]

my 78 Jimmy bounced
when I changed from idiots to tach and cluster
i had to add a seperate ground for the fuel gauge ground
it stopped

my 79
I was worried changing to a spectra unit this summer it would bounce
nope

if it's working right, grounding the sender wire is E,off is over F
I'd check the tank ground for sure

[willett]

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[willett]

My fuel gauge bounces on both tanks, always has, I thought it was supposed to do that.
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[79Betty]

Ill check tonight in the garage and see what happens
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