Jr Orozco

I'm still having issues with my fuel gauge not reading full when I fill up the tank. Where should I start for diagnostics? I already replaced the fuel gauge, and the sending unit twice with no results. 5.7 TPI. Thanks.

thtanner

iTrader: (1)

As long as you filled up the tank and unplugged the connector from the sending unit and tested the ohm reading (should be 100), then you know the sending unit is fine. You should do that to make 100% sure the sender is reading properly.

If that reads fine, then your particular issue is 100% wiring related between the gauge and sending unit. Need to inspect every point of the wiring from the gauge to the bulkhead connector in the back. Check for shorts, weak grounds, etc. It would be a good time to beef up or clean all grounds on the car. Don't forget the one under the carpet under the drivers seat.

2knight

iTrader: (1)

I had an issue on a different vehicle, no matter what I did it wasn't 100% accurate or consistent, but i knew the gauge and sender were good because I replaced them just like you. What I ended up doing is running an extra wire to the sender. I disconnected the sender ground connection at the tank and hooked up the wire and ran it up to my gauges and grounded it with the gauges. That way the ground potential is the same at the sender and the gauge so no false readings.

thtanner

iTrader: (1)

It has since been confirmed his issue is at the sender. He is only reading 67 ohms at a full tank when read directly off the sender connector itself. The sender was tested outside of the vehicle prior to installation with no issue, so my suspect for him is physical interference of the float (possibly fuel pump power wire.)

He also plugged in a spare sender outside of the tank, float set to max, and the gauge worked appropriately.

GeneralDisorder

iTrader: (1)

The issue is the aftermarket sending units. The shape of the float arm is such that they don't go all the way to the top of the tank. The Spectra unit seems to be the best but it's still not right. Not much that can be done since stock units are NLA.

GD

rt66er

iTrader: (2)

I ran into the same problem after replacing my defective OEM sending unit with the Spectra. I was able to add a resistor in series with the sending unit wire (the harness is easy to access under the drivers-side rear seat bottom) to get a more accurate fuel reading. In practice, it's now actually more accurate than OEM. With a full tank, the gauge reads about a needles-width above the "F." When the gauge reaches the hatched mark (1/8th), it will take ~13.5 gallons, or 7/8 of 15.5. However, this also means that "E" means empty. Really, really empty. My past experience with third gen Firebirds is that when it reaches "E", you've still got a gallon or two reserve. Not mine. Not anymore. If you're interested, I can check and see what resistor I used (can't remember now).

Tuned Performance

iTrader: (92)

Wouldn’t it be about 23 ohms difference if he’s at 67 ohms ?

GeneralDisorder

iTrader: (1)

You could install a programmable process controller / digital display that is programmed to sweep linearly through the voltage given by the reduced travel of the sending unit. Such as:

https://www.auberins.com/index.php?m...products_id=19

GD

thtanner

iTrader: (1)

Edit: nevermind