snowgod

I replaced the Fuel Sending unit a few months ago. It worked up until I filled the tank the first time. The tank went to full, then came down to 3/4 and there it sits, (and I thought I was getting awesome mileage) I am just now getting tired of checking the tank to know how much fuel I have. I tested the gauge by removing the sending wire and grounding it to the frame. The gauge goes to full. I checked continuity of all the wires, including making sure I have a good ground. What Gives? I guess next would be to get an Ohm reading when the tank is full, and another when near empty. Does anyone know how to do this?

59er

Snowgod,

I would have assumed that as the fuel gauge positive terminal comes from the ignition switch then the wire going to the fuel sender would be the ground which I would have assumed that when the tank is full then there would be no resistance thus giving a closed circuit thus full voltage to the gauge and as the fuel level goes down then the resistance would increase thus giving less voltage to the gauge thus the needle should drop.

To test this theory I checked my brand new sending unit that was in a box here in my home office but to my surprise there is no change in the resistance no matter where I move the level to. I get a closed circuit between the terminal and the mounting plate.

Either my new sender is a dud or I'm doing something wrong.

Come on guys, Please give us some help!

Mark. :confused:

JohnZ

Mark -

Per Dan Materazzi's article on trouble-shooting '55-'62 Corvette fuel gauge systems in the Winter 2001 NCRS "Restorer" magazine, the sending unit resistance between the mounting plate (ground) and the terminal on it for the sending unit tan wire should measure zero for an empty tank (float all the way down), and about 32 ohms for a full tank (float up). If you show no change in resistance doing this measurement, the sending unit is defective.

59er

John and Snowgod,

I retested my sender as described in John's post but this time used a digital ohm meter and read virtualy exactly as described in that post.

I must have had the other meter on the wrong range or such as the auto ranging meter worked right off.

Thanks John and try this test Snowgod. :D

58Mike

As an aside, my sending unit wasn't working as it was in a car that hadn't been driveable for years. It had all kinds of corrosion and even some rust. So I gave it a 15 minute dunk in my trusty bucket of muriatic acid and voila, works perfectly now. Of course I had to give it a thorough rinse, etc after the acid.

- Mike

snowgod

I tried the Coat Hanger method, hooking an Ohm meter between the Tan wire and the sending unit. Meter stays at 14, and doesnt move when I push the float down. The tank is near full, so I know I am getting full range of motion out of the float moving down and back up. I am assuming that I am doint the test correctly. This bites, the unit is new from Zip Products. It only worked for one tank of gas, and not even really for that long. I put in the unit, filled the tank with a 5 gallon can, it went to a 1/4, I went to the station and topped it off, it went to Full, and hasnt gone below 3/4 since. I guess I will try and get a replacement out of Zip. Could there be something else wrong that caused the Sending unit to fail? I measured the voltage at the sending unit, it was normal.

59er

Snowgod,

To confirm that the problem is indeed in the sending unit and not the gauge I would be doing the test as noted in John Z's post, that is, disconnect the wire from the sending unit and connect the negative probe of the ohm meter to the base of the sending unit and the positive probe to the terminal that had the wire connected to it and it should then show around 32 ohms when the float is all the way up and zero ohms when it is all the way down.

I did this test on my new sending unit and it works perfectly provided you have the meter on the right scale.( I know, I stuffed up!)

I contacted Zip about my unit and they were going to send a replacement right away but I called them the same day and told them that it was my mistake so if yours does prove to be defective they may change it without hassle.

Good Luck.
Mark.

JohnZ

Most of the vendors sell two different C1 sending units - a GM-Delco part, and a Taiwan part; the difference is about $15.00; ask the vendor for the GM part and pay the extra bucks for a dependable part.