Jonmueller1

Fuel gauge needle sits at extreme right when ignition on. I disconnected the positive wire to the sending unit and turned the key on and the gauge needle still sits all the way to the extreme right. I am told that connection to the fuel gauge behind dash is possibly loose. I cannot find any mounting screws that hold the dash in. If I look up underneath the dash I can see the fuel gauge with a circuit board behind it.
My question is, what is the best way to obtain access to the gauge so I can test it and check all the connections. It could be shorted out or a connection, positive or ground is disconnected. How do you get the dash out without damaging the facia. I am new at this so I need to be careful. I could install an aftermarket fuel gauge by wiring it to the power source and to the sending unit. By the way, the sending unit is brand new, was installed during renovation of trunk and fuel tank. Even before that was all done, the fuel gauge was still stuck to the right when the key was turned on. Thanks for your help, JM

oldcutlass

Ground the wire at the fuel tank with the key on. If the gauge goes to E then it's your fuel tank sending unit. The fuel tank sending unit is a rheostat that supplies varying levels of ground. The other side of the gauge is supplied constant 12v.

jaunty75

As oldcutlass implies, the gauge is most likely not the problem. It's more likely the sending unit, and to test it, do what oldcutlass says.

Take that positive wire that you disconnected from the sending unit and ground it. THEN turn the key on. If the needle goes to E, then the dash gauge is fine, and your problem is the sending unit.

A gauge that pegs on F or well past it, as yours does, indicates an open circuit. The gauge itself is just a resistance (ohm) meter, and the sending unit is just variable (0-90 ohm) resistor. The far right (F) on the gauge indicates 90 ohm resistance (or infinite resistance if the circuit is actually open) and the far left (E) indicates zero resistance.

99% of fuel gauge issues are due to a failed sending unit or a bad ground connection where the other wire (black) coming off the sending unit attaches to the body or frame. Before tearing into your dash, verify that the gauge really is the problem with the simple test described above.

If the sending unit is new as yours is, the problem might be simply bad wiring. Perhaps there is an open in the wire between the gauge and the end that you removed from the sending unit. Even though the sending unit is new and you therefore do not suspect it, I would still verify that the gauge itself is or is not working correctly.

Jonmueller1

Jaunty 75 and OldCutlass are correct. I grounded the positive line to the sending unit. The needle dropped to E on the left. Now is that categorical proof that sending unit is bad only or could it also be true that there is an opening in the positive line between sending unit and fuel gauge?? Which would it be? I am going out to check the ground wire by running a separate one from sending unit to ground. If it in fact does work, then the gauge will register true fuel level, right??? The question itself sounds dumb because the grounding of the positive wire that I did meant that the circuit was closed, right?? Thank you. JM

jaunty75

All this proves is that the gauge is ok. Why the sending unit is not sending a signal to it is what needs to be investigated next. It could be a bad sending unit, new or not.

You say you pulled the positive wire off the sending unit, grounded it, and the gauge went to E. You've thus just confirmed that the line from the gauge to the sending unit is OK as long as it's securely reconnected to the sending unit. So there can't be an opening in the wire between the gauge and sending unit because you've just proved that it's intact along its entire length.

The other thing to check is the ground wire. There should be a second wire coming off of the sending unit connected directly to ground, probably in the area forward of the gas tank up under the car. (Unless the ground is through the sending unit itself and there is no separate ground wire. I'm not directly familiar with the wiring in a '64.) If the sending unit was recently replaced, it's possible that reconnection of the ground wire was simply overlooked. Find it, and make sure it's connected to a clean point on the frame or body. Where this connection is made can easily become dirty and corroded over many years, and a bad ground is another common reason for a non-working gas gauge.

nsnarsk65cutlass

X2 on ground wire at sending unit.

Jonmueller1

nsnark65cutlass: what do you mean by "X2"? I went under the car and ran a second ground wire to test and the fuel gauge didn't react, stayed in far right position. Is running a second ground wire what you mean by X2?
Also in reply to Jaunty75: I did check the ground wire from the sending unit to the frame. The spot where it is screwed into the frame was actually previously sanded down to the metal and grounding wire reattached. Still no change from the fuel gauge. So now actually I think we have proven that the sending unit is bad even though I thought the shop had installed the new one I gave them. Its possible either never installed new one or new one they installed is bad. So I now need to get another one and install it. Any other suggestions before I move forward with that? I think they are around eighty dollars or so....Thank you all again for good ideas...JM

oldcutlass

I would assume there is something wrong with your sending unit as you've proven everything to it is ok.


X2 means the poster is the second person to agree with the statement.

jaunty75

x2

Jonmueller1

Yesterday I took the new sending unit out of the box and held it at the side of the car, connected a wire to the positive black wire that goes to the fuel gauge and attached it to the positive connection on the new sending unit. Then I touched the ground wire to several grounds on the car, all with the key in the "on" position. I moved the float up and down and there is no reaction from the fuel gauge needle that sits all the way to the right. I was trying this first before going to the trouble of removing the existing sending unit from the tank which was a new one as well. The only way I get the fuel gauge needle to move is to actually ground the black positive wire itself to several points on the car. My concern is that with this test that I did, if I install this new sending unit, I could get the same result as the one that is already in the car where it is not working when connected properly. Are there any facts that I am missing here? Thank you. Jon M

oldcutlass

If by grounding the wire to the gauge it goes to E, and then connecting it to the sender you get nothing, I'm going to say you don't have a solid ground to the sender. Basically the sender is a 90 ohm rheostat in series with ground.

jaunty75

To second what oldcutlass says, a gauge stuck on F indicates an open circuit. If by removing the wire coming from the gauge and connected to the sending unit from the sending unit and grounding it causes the gauge to move to E, then there is nothing wrong with the gauge or the wiring from the gauge to the back of the car.

If by then connecting that wire to the positive side of the sending unit and connecting the ground side of the sending unit to ground, the gauge still reads F, then you don't have a complete circuit, either because the ground is not really grounded or there is an open within the sending unit itself.

The entire gauge/sending unit is a very simple circuit:

wire from +12 V to gauge --- wire from gauge to sending unit --- wire from sending unit to ground.

An open anywhere in there will cause the gauge to read F all the time. A short anywhere will cause it to read E all the time. If the wiring is ok, then moving the float up and down should cause the gauge to move in a corresponding fashion.

Jonmueller1

Yet again I am stumped. I had the new sending unit installed in the car today and it did not move the needle from F. The mechanic tested the OHM reading on it and he said it was way high, in the 300's according to him. He even tested the positive connection to the fuel gauge using a 10 0hm resistor, then a 20 ohm and the gauge read 1/4 tank , one half a tank etc . He said it looks like the sending unit is bad and it is the second one I have tried on the car. I bought it from OPGI and will return it.
Question one: is it possible these parts are made in China and are cheap imitations of the real thing?
Question two: What would be the most reliable vendor for me to purchase another one?
The 1964 Oldsmobile calls for a 30 ohm sending unit and the 1965 calls for a 90 ohm unit. I specifically requested one for a 1964 wit 30 ohms.
I did do a test on this one outside the fuel tank by connecting it to the positive wire to the fuel gauge and then grounding the sending unit to the car and it would not move the needle on the fuel gauge, when I moved the float arm. I should have stopped there and had a qualified mechanic check it before installing it in the car.
So I can now try and locate a third sending unit, but test it before installing it in the car.
Are there any other facts I am missing? Sorry to be such a bore with all this, but I have to credit the mechanic for testing the sender and telling me the ohms read way too high and that is why it doesn't work. Thanks, Jon M

oldcutlass

Give these guys a shot, they have a 35 ohm spectra unit. You may also be able to pich one up at your local parts house.


http://www.rockauto.com/catalog/x,ca...,parttype,4436

jaunty75

Autozone's website shows availability of three sending units for your car, all made by Spectra Premium.

http://www.autozone.com/autozone/par.../N-ixzguZ8vdfx

Not sure if that means Chinese made, but I wouldn't assume something made in China is automatically of poor quality, and I wouldn't assume that there are dozens of manufacturers of these things, and it's only a matter of finding a U.S.-based one.

There may be one or two manufacturers in the world of sending units for '64 Oldsmobiles, and they're sold through all of the various vendors. For all we know, all sending units are actually made in China and just distributed under different names. I really don't know, but given the state of the world these days, it's what I suspect.

I have a Spectra Premium unit in my '67 Delta 88 that I purchased through Rockauto, and it's been fine.

I see that the OPGI site does not mention the brand or manufacturer of their sending units, although they do correctly state that it's a 0-30 ohm unit. But this is what I mean when I say that you can't be sure that all sending units aren't made in China.

http://www.opgi.com/cutlass/1964/air...tanks/PZ00730/

Jonmueller1

Received replacement unit from OPGI today. Tested it with ohm meter and it registers 30 at empty and zero at full. The one I had the shop install was in fact bad, it had a real high ohm reading, way above 30.
Should I attempt to install myself? The opening is accessible if you put the car on ramps and it faces the front. Tank doesn't need to be dropped. I will test it by hooking it up using alligator leads to the sending unit wire and ground with the front door open and hopefully the fuel gauge will react accordingly.
Would it be better to have it installed using a lift gaining better access? I am worried about spilling gas or potential for fire if I try it myself. It seems fairly simple to release the ring and pull out the sending unit and reinstall new one, but I don't want to be a fool. So any opinions are welcome on this issue. OPGI didn't give me a credit for the defective sending unit because it had gas on it from the installation...I should have studied U-Tube first and learned how to test it first before ordering it installed. I am hesitant to go back to the same shop, labour very expensive, but it has to be done safely.....Thanks, JM

oldcutlass

It's not a hard job. I would run most of the fuel out before starting to replace as it would be easier to lower the tank if you needed to. The risk factor is no more than when you fill your tank at the gas station.

flyinmy172