My fuel gauge is straight up stuck on full. Normally I would think the sender has been shorted to ground and that is why it does that, but the problem is that it does not move one bit whether the car is off or on. So I am thinking the gauge is jacked.

I bought a 90 ohm gauge from summit and I am guessing the pink wire is the wire that needed to be for the sender.

Anyone else thinks this may be the gauge?

 

It sounds like it might be.At any rate it's probably easier and cheaper than the sender unit.

 

If I had too bet money on it, I bet on the sending unit being bad. All my gauges freeze at the spot they were at when the car was turned off, The fuel, temp, oil, even the tach are stuck at there last position before loss of power.

BTW a shorted sending would make the gauge read empty, the sending unit is either open, there is a bad ground for the sending unit, or there is a broken wire.

Good Luck

 

If the sending unit was bad, like you suggested then "power" to the gauge would not be an issue. Since the only wire that comes from the pump to the gauge is the sender resistance. Which in return would be the gauge.

If the sender wire was broken the gauge would turn off when the car was off and not stay in the same spot right? Unless I had two seperate problems.

 

There are 3 wires to the gauge Ignition, and sending unit (a 0 - 90 ohm potentiometer), 0 ohms = Empty – 90 ohms = Full.
The circuit is a series circuit with the +12v going to the coil of the gauge, then to the POT and then ground. All analog electrical gauges are in reality current meters (Ammeters). The needle moves with changes in current. As the POT changes it's resistance the current in the circuit will change thus moving the needle. If there is a break in the circuit the resistance will be infinite. The meter will read Full.

I copied the following from Autometers web site Tech info section:

Q: Why does my fuel level gauge always read past full?

A: If the gauge increases in resistance from Empty to Full, such as 0 to 90, 0 to 30, or 16 to 158, and assuming that the gauge is properly matched to the sender then read on. The most common cause of this type of gauge to read over full is typically due to no ground at the sender, an open circuit, or break in the wire going from the gauge to the sender. A quick and easy way to check the gauge is to remove the sender wire off of the back of the gauge, leave the power and ground hooked up and use a jumper wire to connect the “S” terminal of the gauge to ground. Turn the power on. If the gauge responds by going to E, then you have proven that the gauge responds well. Jumping the “S” terminal to ground is the same as 0 ohms of resistance to ground. Having no wire or jumper on the “S” terminal is infinite resistance to ground which is much greater than the gauges F reading which then will cause the gauge to read past full. If when you jumpered the “S” terminal to ground and the gauge did not respond by going to E, you will then check power, check ground, check the ground you jumpered to, then lastly check the model number on the gauge to see if you have the correct gauge (one that goes up in resistance reading as the fuel level increases).


For some reason the gauges in our cars and most others, the needle stays where it was at the moment the voltage is removed. I just turn my car and to prove it to myself, my oil pressure stayed at 30PSI, my fuel at half tank, and my Tach at 1000RPM.

I think the reason the gauges don't return to zero (empty) is because as the tank empties the reistance of the sending approaches zero raising the current. It takes more current to return the gauge to empty and when the engines is off the is no current, so it stays put, until it gets it's power again. Since if I'm right your guage never has any current do to the reasons I've stated.

 

Well either way, I will be cutting an access panel for the fuel pump anyways, so if I have to replace the sender it wont be much trouble I guess.

 

I'm replacing my sending unit also, but I modified the stock assembly with an Autometer unit because Chevy wants $600.00 for the entire assembly. The tubing, sending unit and fuel pump combo and won't sell them separately. That creates another problem the Autometer unit is 240 ohm to 33 ohms and requires one of their gauges to work. I bought another cluster from "Pick Your Part" and I’m in the process off placing it in the stock location with a little hacking and cutting.

If someone knows a better way let me know. I tried getting a used one at the junkyard but they were not any better than the one I'm replacing. I think my way will work fine though for a lot less money.

 

Well I have a 140 mph cluster and would hate to get rid of it due to a crappy gauge.

 

I'm only replacing the fuel guage.

 

I am having the same problem so I replaced the gauge in the dash today and it is worse. I replaced the fuel pump last weekend and i took the whole sendind unit aprt and thoughly cleaned it and sanded the spring contact and housing so it would have a good connection.

I guess my next step is to check continuity thru the wire to see if its broken. Does anyone know where that wire is on the drivers kick panel? Is it in the two large black connectors one goes to the fuel pump relay under the hood and what color was the wire on the 87 5.7tpi

 

I too have the same problem with my gauge constantly reading past full. This has a lot of great information in it. I'll check these things out next time I'm at my shop replacing my (hopefully) bad fuel pump.

 

Well still no luck I tested continuity thru the pink wire all the way to the dash but I did not check to see if there was a break in the gauge cluster. I am guessing that my sending unit is gone. what bothers me is I cleaned it and checked continuity through it.

I guess I will add that to the list of need items