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Discussion Starter #1
Hello

Here is my problem. I Installed all my Gauges and everything is working fine but, The Gas gauge is jumping around.. I have checked all the wires from the tank and the ground seems to be ok. I did notice the Ground on the back side of my gas gauge is also grounded to the same ground as my Tack, Could this cause me grief....Oh this is in a 78 Camaro Z28.. Any helpfull hints would be great....

Cheer's Jim
 

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jumpy gauge

Doc here :pimp:

A few things can cause a "jumpy' Gauge... First is this the only gauge jumping? Or do you see it in other instruments?

If it's just the fuel gauge,

The Tach ground would only cause a problem IF:

The ground to BOTH were faulty. Then the ground from one gauge to another would "Load" intermittently, seeking a ground in series through the other gauge.

To eliminate that problem, ground two wires to the frame/body, firewall or directly to the battery and use those as known good grounds.

NEXT: The sender wire going back to the tank could be intermittent.

If you remove or short the ground source from the gauge sender input, the gauge will climb...If you do it rapidly (as in intermittent), It will jump or oscillate. BE sure you have a ground wire from the sender ground lug to the frame, and it is good!

REMEMBER! most folks forget, The tank is held in by steel straps, with Bonded rubber between the strap and tank, and the filler neck is held in place by a big rubber grommet...leaving the fuel line as the only ground...and none if you have a rubber hose between the line and the fuel pump, or any fuel filter before the fuel pump!

The best way to test it is pull the sender wire at the tank, and get a 50 ohm and a 100 ohm 1 watt resistor and hook it to the sender line and ground.

50 ohms should give you about 1/2 tank, 100 ohms should give you something above 3/4 of a tank(ballpark figures).

Hook either up and watch the gauge, It should be steady on the reading, Then "Bounce the car...real good, jump on the bumper hard and watch the gauge it should still be steady This should eliminate a "Loose wire" symptom.

NEXT and most likely, The Sender Rheostat on the float assembly may have worn out, causing the float arm to be loose and intermittent against the rheostat element..making the signal "Jumpy" every-time the fuel sloshes around. The only cure for that is get and install a new sender.

And more rare, some vehicles have instrument Regulators, (Stock mounted gauges) These have been known to be intermittent when they start to burn out, Thermal Shut down. If your using after~markets then I would doubt this is your problem.

Keep Us posted!

Doc :pimp:
 

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Discussion Starter #5
Thanx Guys

Thanks all for the input. I will try some of these hints as soon as the snow stops... I guess it's time to put the car away and focus on reading Hotrod Mag's.

Just out of Curiosity has anyone here bought a crate engine from GM and had trouble with it blowing blue smoke out the tail pipes?
I have a 350\ 300 Hp crate. I have had it rebuilt 3 times because of this and it still smokes really good about 1 liter every 200 Miles.
Last time i stroked it new cam Keith Black pistons and rings new crank the whole nine yard's..And smoke is still present...

Cheer's Jim
 

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smoke

Doc here:pimp:

Nope, never heard of the problem before, But I suppose it is conceivable that a cylinder could be warped or "Out of round" since new...but on 3 rebuilds, I would think a good machinist would have found the condition...

Doc
 

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smoke bomb

Hey take a good look at your intake gaskets & your PCV valve if you have one. Did you use the lame old stock type valve seals? molly rings can get a glaze during break-in.
 
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