Fuel Gauge and Sending Unit

[Robert S.]

good morning from California

Q re: 62 sending unit.

Replaced sending unit recently. (Gauge works fine)

"Dry" tested before installation. Gauge traveled full range.

Installed new sending unit. Gauge only reads half when tank is full.

Problem appears to be w the sending unit connection: when I loosen the connection (disconnect) and manually move the connection up and down the sending unit screw, gauge will move to full. Once the connection is restored and retighten, gauge again only reads half.

Any thoughts out there? Appreciated.

[Mike M.]

Re: Fuel Gauge and Sending Unit

place an external tooth lock washer between ground spade and the ground source on the tank.remove oxidation fromground spade and ground source and apply a dab of dielectric grease to both. mike

[Roger O.]

Re: Fuel Gauge and Sending Unit

If you remove the brown ohms wire from the sending unit at the tank will the gauge go to full ?

[Robert S.]

Re: Fuel Gauge and Sending Unit

Yes

when I touch the wire to the ground wire, it goes to empty

[Robert S.]

Re: Fuel Gauge and Sending Unit

Thanks, Standby.....

[Robert S.]

Re: Fuel Gauge and Sending Unit

Cleaned ground, used internal washer (only type I had at the garage)

It appears to be a part of the solution as the gauge now registers a little above 3/4.

there is a second ground I added. I will clean that one, buy a few external stars and see what happens.

Looks like you put me on the right track. I may have to repeat this process at the instrument panel ground to see if I can get the gauge to read F (filled it up this AM)

Thanks for the help

[Robert S.]

Re: Fuel Gauge and Sending Unit

Mike McCagh advised to clean ground connection, add ext. star washer.

It appears to be a major part of the solution as the gauge now reads 3/4.

I will clean the ground located at the instrument panel. Just need to remember where it is.

thanks for your help

[Roger O.]

Re: Fuel Gauge and Sending Unit

I'm going to be surprised if a better ground helps the gauge get closer to full. Its usually the other way around.

[Robert S.]

Re: Fuel Gauge and Sending Unit

I'm going to be surprised if a better ground helps the gauge get closer to full. Its usually the other way around.

Roger

So far it appears that the improved ground has increased the "range" of the gauge. Pls provide more info re: "the other way around".

I will not be able to get to the gauge until Saturday, so I would appreciate hearing your thoughts.

thanks.

[Roger O.]

Re: Fuel Gauge and Sending Unit

Working from the "gauge end in the dash" a better ground on the neg side of the "gauge" (not the ohms wire coming from the tank) itself will increase the range.On the gauge itself you have 3 terminals :: Pos , Neg and Ohms (or tank input). A dirty Neg will cause the gauge to read towards empty and cleaning that Neg will make it read closer to full.

But earlier you were working back at the tank and this only involves 1 wire the ohms wire or tank signal wire. This 1 wire sends a signal to the gauge in the form of a ground ranging from a great ground ( EMPTY) to a very poor or no ground (FULL).
You said earlier grounding the ohms wire at the tank made the gauge go to Empty...so a really good ground makes the tank read closer to empty.
You said removing the wire made the gauge read full. Removing the wire is the ultimate bad ground which makes the gauge read closer to full.
Thats why my thoughts were a better ground at the tank through the ohms wire should make the dash gauge read closer to empty not full.

I would use your meter and read the tank sender. One probe on the sender metal base and one probe on the sender terminal. Your reading with a full tank should be 90 ohms plus , 1/2 tank should be around 45 ohms and empty should be down around 0 to 5 Ohms.
If your not getting a 90 ohms plus reading with your tank being full then the sender is bad.

[Robert S.]

Re: Fuel Gauge and Sending Unit

Roger

Thank you for the helpful information and insight and for taking the time to reply.

I will perform the checks on Saturday, and somewhere between HS football, soccer and cheer I will get back to you.

thanks again.

[John H.]

Re: Fuel Gauge and Sending Unit

Your reading with a full tank should be 90 ohms plus , 1/2 tank should be around 45 ohms and empty should be down around 0 to 5 Ohms.
If your not getting a 90 ohms plus reading with your tank being full then the sender is bad.

Roger -

His car is a '62, so his resistance range in the sending unit is 0-30 ohms; half-full will be about 15 ohms.

[Roger O.]

Re: Fuel Gauge and Sending Unit

Roger -

His car is a '62, so his resistance range in the sending unit is 0-30 ohms; half-full will be about 15 ohms.

Thanks John I knew that darn-it and if I would have reread my post I might have caught it. I've been working on more C3s than anything else lately.
Sorry for the wrong info Robert I hope you see this before Saturday.