Gas Gauge on 48 Pontiac

[Rich48]

Let me start by saying I am new here. Hope I don't embarrass myself to much. I recently acquired a 48  Pontiac Streamliner Coupe project. There are a few loose ends to be taken care of on the car but mainly the majority of the work is going to be in the interior. So if you know a good interior guy in Michigan that would be helpful too. Right now I am trying to get the gas gauge to work. The previous owner has installed a new sending unit and it looks like he attempted to do some wiring behind the gauge itself (new resistor). My question is this. Doesn't the sending unit ands the resistor at the gauge have to be "matched" in some way? I cant find numbers on anything so I really don't know what I have. I am thinking of just starting over with new parts. Is anyone familiar with this repair and what do I need to make this work? 

 

Also I am looking for the following parts:

Chrome "waterfall" trim for the hood

Arm rests for front doors

Sun Visors

 

Anyone know where I can find any of these ?

Thank you for your help

[GARY F]

For parts if you belong to the Pontiac/Oakland club in the mag. there are parts  new/ used  suppliers . Can't help with the problem. if you have a shop manual there should be a diagram .

[Rich48]

Ok thanks. Guess I didn't think it would hurt to check another as site.

[Bloo]

All GM gas gauges of this period are the same electrically. It is zero ohms (or very close) for empty and 30 ohms for full.

 

The sending unit therefore needs to be a 0-30 ohm unit for a GM car. If it isn't, it won't work with the stock gauge.

 

Don't forget to zero your ohmmeter before you test. Short the leads together, and if its analog there will be a little thumbwheel to zero it. If it is a modern DMM there should be a "delta" button.

 

If you test from the wire that goes to the gauge from the tank (use one meter lead) to chassis ground (use the other), with the gauge disconnected from the wire you are testing, you should have something inbetween 0 (almost) and 30 (or a wee bit more). It should roughly represent how much gas is in the tank, too.

 

If it is way high try grounding the tank to the chassis better. Do it from a sending unit screw if you can reach it. If not, get a good connection to the tank somehow. If that doesn't get you something between 0-30 ohms, and it is still high, either the wire is broken somewhere between where you are testing and the tank, or the sending unit is bad. You may need to pull the tank at that point.

 

If it is stuck low, and the tank isn't close to empty, either the wire is shorted on it's way to the tank or the sending unit has a problem, probably a sunk float. If you cant find a short, you may need to pull the tank.

 

That should suss out the sending unit. The gauge itself needs power from the ignition switch on one terminal and the sending unit hooked to the other. It matters which terminal is which.

 

In addition to the two terminals there is a ground for the gauge itself. The gauge touches something on the cluster (you can see the spot if it's apart), and the cluster gets its ground through the dash. Fresh paint can screw this up. The gauge itself must have it's own good ground.

 

To test the gauge, if you disconnect the wire going to the tank, and the ignition is on, the gauge should peg full. If you short the gauge terminal to ground, the one you just took the tank wire off of, the gauge should peg empty. If it won't do this it wont work. Check power and ground to the gauge (most likely) or you might just have a bad gauge (less likely).

 

I don't know what resistor you are referring to. As far as I know it shouldn't have one. Is this a 12v conversion? If so, maybe someone tried to use a resistor to drop the voltage. That doesn't work well because the load isn't constant. Some have used a "RUNTZ" voltage dropper. In various forum threads I have been in some swear it works for a gas gauge and others swear it doesn't. I've not tried it myself so I don't know. It does sound more likely to work right than a resistor.

 

Edited October 15, 2020 by Bloo (see edit history)

[Rich48]

Thank you for the testing info. I will give that a shot. Yes it is a 12v conversion. He has the same type of "resistor" on the temp gauge. It is showing a temp as the motor warms up but not sure how accurate it is yet. Trying to work thru one issue at a time. I got all winter. Thanks again for your time. I appreciate it.