Need Help With Fuel Gauge and Sender Unit

[DeadMansOhms]

Hi. New here to this forum. Found it by trying to find answers to my problem. Any help is greatly appreciated.

I have a '69 Chevy C20 and everything was fine with my fuel Guage until I went to fill up my tank when it was empty and noticed when it was full my gauge only went to half. Now I have half a tank and it says empty. So I checked the wiring and it looks good. Did a resistance check on the sender unit. It seems to be correct with what's in the tank. So I'm guessing it's my gauge. I guess there is a resistor on the back of the gauge. Could that be the problem? If so can I purchase that only or would I have to get the whole gauge.

One other thing I noticed is, when I checked the resistance at the sending unit, it only showed me a value with the key off and it was nothing when the key was on. Don't know if that's normal.

Thank you for reading and I hope someone can help.

[demian5]

Yes you can buy a new resistor. And you can change without pulling cluster. Let us know how it works out. That was the issue with my sons truck and it was just like you described.

[DeadMansOhms]

That's what I'm thinking. Now I just need to find out where to get one or make one.

[LockDoc]

Originally Posted by DeadMansOhms

That's what I'm thinking. Now I just need to find out where to get one or make one.

Truckandcarshop has them.

http://www.truckandcarshop.com/trucks60_72/t60_045.html

Here is a post by bigbadchev72.

After ordering from fix-a-gauge and having horrible service and a month of waiting I finally got a resistor in the mail with a radio shack sticker on it, 87ohm resistor and you are good to go.

And a chart posted by VetteVet.

[HO455]

Welcome aboard! Here is a link with some helpful information. Good luck!

http://67-72chevytrucks.com/vboard/s...d.php?t=640615

[demian5]

The truck and car shop ones are the ticket, and don't let them fool you that they only have ones for 67-72 because these are the sames ones on 73-87.

You can also just buy resistors from an electronics store, that is how we have fixed other gauges.

[DeadMansOhms]

Well I pulled the resistor off the gauge and checked the resistance and it was 90 Ohms. I feel like that's correct and it would mean it's not bad but maybe I'm wrong. If it is correct then I assume the gauge is bad? What do you guys think. I almost positive the sending unit is good.

Pulled the wire - gauge went past full
Grounded wire - gauge went to empty
Check resistance to sending unit - matches what's in the tank.
Gauge resistor Ohms at 90

What else should I check? Or should I just star replacing things.

Thank you again to who's helped so far and any who helps after.

[JMD]

I bet your float filled up with fuel and sank to the bottom of the tank. Pretty common issue, especially if you have an aftermaket sending unit with a brass float. If you decide to get a new float make sure you get a plastic one, half of the aftermaket brass floats are garbage from the factory and you'll run into the same problem a few weeks down the road.

[JMD]

Pull your sending unit out of the tank, unclip the float and give it a shake. If there's any liquid in it, throw it in the garbage and pick up a new plastic float from Summit. Here's a link...
https://www.summitracing.com/parts/o...SABEgK4TPD_BwE

[VetteVet]

While you have the sending unit out of the tank, connect everything up to it and ground the mounting flange to a good ground, with the key on move the float arm through it's motion and observe the gauge for the correct travel. If it follows the full travel it will prove the gauge is good or bad.

If the float is full of gas it takes more gas in the tank to raise it than the gauge is showing which is the indication you say you are getting.

A bad resistor will usually only indicate 1/4 th of a tank no matter how much over that you have.

I think JMD wins the prize on this one.