Gas gauge reads 1/4 tank on full tank of gas

[tucsonjwt]

If you replaced your sending units with aftermarket units (I used Spectra), then you will get a bouncing fuel gauge on bumps, turns, stops - at least that is my experience. But I think you are in a whole different ballpark - electronic fuel injection, different sending unit, even different type of gauge required - I would suspect. Unless, of course, if you topped it off with a carbureted intake, etc. How much of the modern 5.3 setup did you use? I am thinking that engine is not set up for old analog gauges, with regard to electronics controlling it. I think the hot rod conversion guys probably figured this one out already - might try them.

[78-5.3]

Originally Posted by tucsonjwt

If you replaced your sending units with aftermarket units (I used Spectra), then you will get a bouncing fuel gauge on bumps, turns, stops - at least that is my experience. But I think you are in a whole different ballpark - electronic fuel injection, different sending unit, even different type of gauge required - I would suspect. Unless, of course, if you topped it off with a carbureted intake, etc. How much of the modern 5.3 setup did you use? I am thinking that engine is not set up for old analog gauges, with regard to electronics controlling it. I think the hot rod conversion guys probably figured this one out already - might try them.

well its injected but i used a corvette /camaro z28 tpi pump they fit like a 87 pump do and they are analog gauge too i still have a 87 camaro gauge that i tested with as well same thing!!!

[tucsonjwt]

OK - then its off to the 5.3 conversion project pages. I see somebody has an analog gauge in his square body with a 5.3 conversion over there - I know you are probably already a resident over there - but they would know best.
All I know is trial and error - mostly error.

[joe231]

Originally Posted by ebgwd

So, would it be possible to pull the fuel gauge and check the voltage there?
My tank is full and the voltage is just under 12 vdc.
Seems like the voltage should be lower.
Mine is a 86 C-10 and pulling the full gas tank is harder but appears to be necessary. Do you agree?

When I plug in the gauge and only have 2 of the 3 pins on the back of the gauge inserted into the plugs that are in the dash, the gauge will read full. When I seat all 3 pins into the plugs the gauge reads just above 1/4 tank, as shown.

Finally figured that to take resistance readings, switch needed to be OFF.
Negative lead is connected to hard ground on frame of truck.
Left side connector is 12vdc when switch is on.
See photo and give advice. The more I read the more I don't really know about 12vdc circuits.
Thanks

Ok, let me see if I can explain this

here are the 3 pins looking at the back of the cluster

black is ground
red is ignition hot
purple is the fuel gauge wire from the float
key on you will have full battery voltage on the red pin
you need to check the resistance of the purple wire to ground. with the tank full it should be close to 90 ohms.
you can place one meter lead on the purple(should be the right pin) and one lead on the black (bottom pin) to check this (with the key off).
the circuit is completed (to ground) through the float resistor, higher resistance means less voltage across the gauge and the needle moves towards full, less resistance means more voltage across the gauge and the needle moves towards empty. 90 ohms should read full and 0 ohms should read empty.