Is it the sender or the gauge?

[garment]

The gas gauge needle on my '83SC has a tendency to get sort of stuck on the 1/2 mark, dips down to what I assume is the correct amount of gas at or below the 1/4 mark, and then hops back up to the 1/2 mark. The "low gas" idiot light comes on during the dip down. It seems to read properly at levels above 1/2 tank (or at least the needle doesn't bounce around), but doesn't really read "full" even after a fill-up. The dip seems both intermittent and random.

Does this sound like the gauge, or the sender? I assume that both are original to the car, I've only had the car a bit over a year.

Thanks, Pelicans!

A faulty fuel sender is quite common. That the low level idiot light comes on indicates to me that the sender is the cause of your problem.

You can do do two things: replace the old faulty one by a new sender or just take the sender out and take it apart. Repair could be possible.

Simplified, the sensor basically consists of a resistive wire with a float running along the wire. The position of the float is related to the fuel level, resulting in a resistance/current positioning the needle in the gauge. The low level control light is actuated by a switch just above the lower end of the wire.

Here on the board is a nice technical article available which might be helpfull for your test and repair or replacement.

Pelican Mini-Technical Article: Repairing the Fuel Tank Sending Unit

I hope this will help,

Otto

[porwolf]

Sounds like the sender. I had similar problems and fixed them by repairing the sender as in the article above. Not that difficult but you have to treat the sender interiors delicately.

[blucille]

best to seek out a friend with a similar car, the senders were quite standard from year to year.

this sounds like exactly the symptoms I had on my '79, and a bad gauge was the cause.

[porwolf]

Here are threads for the fuel sender unit reair that I saved. They should help:

fuel guage needle is stuck???

fuel guage needle is stuck???

Broken wire inside fuel tank sending unit

83 911 gas tank fuel sending unit help

Fuel Gauge

Fuel level sender diagnosis...

New to Pelican and new 911 owner

[mytoy]

I have the exact same issue as you described except that when mine drops down to the 1/4 mark and the low gas light will stay on. Upon fill up I know that it is low on fuel and therefore the sender must be working. I did replace the sender anyways just to ease my mind. This did resolve the issue for one tank full then it reverted back to normal erratic operation. I can tap on the gauge when it has been at the 1/2 point for some time and it will drop down to read the actual fuel. So I now know that the gauge is the faulty one. Just haven't had the time to actually look into it yet.

You might try tapping the gauge after it has sat at the 1/2 way mark for some time and see if it moves. If it does then I would suspect that our gauges are sticking and that the sender is not at fault.

[garment]

OK, so I pulled the gauge, used an emery board on all the contacts (shiny!), and still have the same problem. On to the sender...

I pulled the sender, and checked the ohm resistance at the terminals as per Bentley. My "empty" float position (checking across the "G" and "31" terminals) seems out of spec - it's reading 68.2 ohms, and Bentley claims a minimum of 69.4 in this position. Can this 0.8 difference be this clue that I need a new sender, or try to repair the one I have?

I also don't get continuity on the "W" and "31" terminals, Bentley says I should - more bad news?

[porwolf]

Originally Posted by garment

OK, so I pulled the gauge, used an emery board on all the contacts (shiny!), and still have the same problem. On to the sender...

I pulled the sender, and checked the ohm resistance at the terminals as per Bentley. My "empty" float position (checking across the "G" and "31" terminals) seems out of spec - it's reading 68.2 ohms, and Bentley claims a minimum of 69.4 in this position. Can this 0.8 difference be this clue that I need a new sender, or try to repair the one I have?

I also don't get continuity on the "W" and "31" terminals, Bentley says I should - more bad news?

I don't think O.8 ohms makes a difference. What would make a difference is the Ohm readings while the float moves up and down. I would take off the sender's aluminum shroud, inspect the free movement of the float and take Ohm readings while sliding the float up and down.

Continuity between "W" and "31" terminals should happen when the float is at the bottom of the sender. That continuity closes the circuit for the "reserve" light in the gauge. When the float is at the bottom it shorts out 2 contact pins there. That continuity closes the circuit for the "reserve" light in the gauge. The reserve light contacts could be coroded and can be cleaned.

[john walker's workshop]

the sender can get kinked when the top of the tank gets sucked down by vacuum or just dented. feel the tank top in front of the sender and see if it is flat or concave. the sender contacts the bottom rear of the tank when this happens.

[garment]

I didn't notice an dent, but then again, I wasn't looking earlier. Will take a look. However...

I cleaned the sender per the mini-guide I found on Pelican, fired up the car, and had the same issue. Ordered a new sender today, but I put 5 gal in the tank, so I don't get stranded, and now the gauge reads correct (I think). So now I don't know what to think about the sender, other than the fact that I don't want to get stranded, so maybe best to spend the money and get a new one to be sure.

the sender can get kinked when the top of the tank gets sucked down by vacuum or just dented. feel the tank top in front of the sender and see if it is flat or concave. the sender contacts the bottom rear of the tank when this happens.

[john walker's workshop]

the depression may not be real obvious, just a slight dip.

[garment]

Tried cleaning the sender, and had the same issue. New sender from our host seems to have solved the issue. Thanks for all who responded!