[Joel Koontz]

It appears that the sending unit in my 68 Lemans has failed.

It did so, midway through a tank of gas from a non top tier gas station that I have never used before.

Does/can poor quality gas cause sending units to fail?

If so, any way to bring the sending unit back to life?

I am running a Tanks Inc. in tank Fuel Pump so I don't need fuel pickup etc.

What is the best sending unit for me to run?

[JLMounce]

Are you running the tanks in sender as well?

Their basic sending unit is somewhat of a notorious piece. Mine worked for about 3 weeks and stopped working.

It's probably just coincidence that it happened after filling up at an unknown station.

The tanks inc floatless sender is a bit expensive but is the one most people recommend with their tanks.

[Joel Koontz]

I am using stock GM sender. I modified stock tank to use Tanks Inc "insert" about 10 years ago

[Joel Koontz]

I am using stock GM sender. I modified stock tank to use Tanks Inc "insert" about 10 years ago

[Skip Fix]

I've got a NOS sender for my 78 I bought from GM pulled it out hooked an ohmmeter and shot. Was good when I bought it about 82.

[Tom Vaught]

Have you actually pulled the tank fuel sender out of the tank?

If you did that and saw that the housing (plastic) was deteriorated then I would blame it on the fuel attacking a plastic sender unit housing that was not designed (years ago) to be compatible with today's 'Corn Gas'.

Tom V.

[codyyy]

From what I have found, the rheostat inside the unit either becomes corroded or loses connection. It is basically a bunch of thin wire wrapped around a piece of metal (or plastic in newer cases) with a needle that brushes up against it when the float moves. Sometimes they'll wear out in a certain area like the middle if you like driving around with half a tank of gas. Bending the tabs in the case, taking the lid off and carefully cleaning the inside and slightly pushing in the brush strip to tighten up the connection may work.

[chevymad]

https://www.gmforum.com/2000-2005-90...roblem-231321/

[Tom Vaught]

Thanks for the GM Info

Tom V.

[Joel Koontz]

I have not yet pulled the sender from the tank.

Prior to my initial post I had:

1. Grounded sending unit wire at connection in trunk and gauge needle went from out of sight full to empty.

2. Pulled ground wire near tank, cleaned wire and ground area, then reinstalled with no change(still OOSF)

After my post at 7:03 I partially dropped the tank and reached up and tried to move the SU wire. It did not seem to move, but the gauge is now working.

I assume this means I have a problem with the SU wire or connection at the SU.

I have car on lift with less than 1/4 tank so I will pull tank/SU and check wires/connection, probably today.

**

Even though I may have found the issue in my specific situation, I am STILL interested in understanding why the SU fail.

**

I have a C5(2000) Corvette and several years ago I had issues with one of the SU on it(C5 has 2 tanks and 2 SU).

At the time, I read a bunch of stuff on Corvette Forum about the issue and many there recommend Chevron Techron.

Some on CF also suggested that removing SU and cleaning contact with pencil eraser or fine sandpaper might restore function.

I tried Techron and cleaning the contacts w/o success. In my case there appeared to be too much wear on the contacts on right tank SU and I ended up replacing the SU in right tank.

It has been good since then, but I do add a bottle of Techron to it every few fillups as a precaution..

This thread has info/photos on C5 SU:

https://www.corvetteforum.com/forums...ge-issues.html

It has been a long time since I have seen a Pontiac SU. Does it have exposed contacts like the C5 SU that could be manually cleaned?

[MilesM]

Mine stops working after car sits over the winter but starts working after driving it around and putting gas in it. It gets Corroded

[68azbird]

Had the same problem in my bird. Pulled the sending unit out and it was completely covered in rust like it had been sitting in the ocean. Wire wheeled it all off and cleaned the rheostat with fine sandpaper. Back in working order now.

[Greg Reid]

Take a look at this post- It's part of a 6 or 7 page sticky topic in the Electrical forum..
http://forums.maxperformanceinc.com/...0&postcount=26
The issue on many of the originals will be the same...rust or corrosion on the ribbon cable to post junction. On the repops, sometimes it just may be poor quality construction and materials.
Here's a link to the entire thread. Following the process outlined in this thread will probably fix 90% of the sending unit/fuel gauge issues.
http://forums.maxperformanceinc.com/...d.php?t=593429

[Joel Koontz]

I pulled tank and sending unit and cleaned the rheostat contacts with fine sandpaper and I tried to move around the wire connections on the SU to make sure they were making good contact.

Reinstalled and the gauge read empty with 1-2 gallons in the tank so the work initially seemed to be a success.

I then took it to gas station and filled it up and the gauge is now OOSF again.

I will probably want to buy a new sending unit at this point.

What brand of SU are best?

What ones should I avoid?

What brand/model and where to buy.?

RockAuto has several, are any of them any good?(I don't need fuel pickup or return the lines, they will be capped)

[Ben M.]

Moisture in the tank from gas on cars that sit often seems to cause corrosion. I've taken a dozen or so connectors apart and usually it's the ribbon braid connection on the original styles with some added impedance in the rheostat area. I know if the corrosion is minor a bit of driving and several fuel-ups tend to get things working again.

I've always bought the Spectra units when I could get them and haven't really had issues in the last 7-8 years on them, but then I do my best to drive my cars as much as I can.

[Greg Reid]

You really need an ohm meter/volt meter to check one properly. You can't really look at an electrical connection and judge it 'good'. You can judge one 'bad' but just because it looks ok...
As for replacements, I got both of mine at Advance Auto, along with a tank. If I'd known what I know now I would have held on to the originals though.

[Joel Koontz]

I changed the Fuel SU today. I installed a Spectra unit that seems to be working well, although I have not yet filled it up to verify that full indicates as full on the gauge.

I tested the original SU and the Ohm readings were correct up to about 1/2 way of the arm movement. After about 1/2 way it showed no connectivity.

The reading was the same at the SU as it was at the terminal on the top of the assembly.

[goatman65]

Bought one from Summit last week it is actually from OPGI and made in Chia. It is junk. It reads 1/4 when it should read 1/2 and reads full when it should read 3/4. I ordered a Robbmc unit yesterday with 1/2 inch pickup and its made in USA. Hope I have better luck with it.

[gtofreek]

I have had 4 senders go bad in recent years. All were new to start with, and within 1-2 years they quit working. 2 in my 99 Monte Carlo, and 2 in my 87 S-10 pickup. The originals worked until I changed them. The new ones don't last. I blame the fuel of today, but not sure about that. It's just that years ago, I never had sending unit problems, now I can't seem to keep a fuel gauge working more than a year or two. Good thing my vehicles have trip meters to keep track on mileage on a fill up.