The Stovebolt Site Forums The Shop Area The Electrical Bay Gas Gauge Not Working

I replaced the original leaking gas tank with new and the sending unit was replaced a few years ago. The gas gauge was working fine before the replacement but does not work now. When the ignition switch is turned on the gauge needle pegs to the full level. The sending unit resistance measures 1.4 - 31.2 ohms. Measuring the voltage from the sending unit to the gauge measures .07 vdc to 2.7 vdc but has no change to the gauge reading. The grounds are good from the sending unit to tank, even running a separate wire from battery positive post (GMC positive ground) makes no change. Could the problem somehow be with the gauge?

Sounds like an open ground some where. Possibly in the sending unit. If you put a test light on the sending unit stud will the gauge move off full then? If so you probably need to pull the sending unit and inspect the wiring inside.

Open circuit. Bad connection somewhere.

Good luck. I have s similar issue. When I fill the tank it buries the needle to the right. When the gas level gets to about 1/2 to 3/4 of a tank it starts reading correctly.

Does your gauge stay buried or does it drop any when the gas level drops?

See the picture in the left margin of the little boy praying? Type “Gas gauge not working” in the box and click the search bar. Be prepared for a good days reading. This question comes up at least once a month and the discussion is always the same. Stovebolt search is your friend. Good luck

You probably know this already but the thing about the fuel level sender is all about ground. That is what the variable resistor in the sender is doing...allowing either full ground or limiting the ground connection by increasing resistance. At empty, you'll have 0 ohms resistance in a perfect world. At full, you'll have 30 ohms resistance in a perfect world. Unfortunately none of the senders I've bought & tested sold by any of the usual suspects will test this way, although yours is close enough. The only sender I've found that will register the exact values is sold by a seller on eBay whose ID is renbusan. But you have either a ground problem or a sending unit problem, I think. Good luck.

As by now, with previous input, you probably figured out that you have a ground issue. The telltale sign is the gauge pegging fuel. You dont need luck, you need to look at what you did.. Especially if it worked just fine prior to the tank replacement. Double check what you did because you did it. Its definitely an open ground problem.

I smoked the sender doing a bench test so have ordered a new sending unit from Carter. I appreciate all of your input and will update when the new sender is installed.

Bill, sorry to hear of the difficulty.

If you smoked the sender, it means you applied voltage to it. It is not supposed to have voltage to it.....or you forgot you have positive ground and applied voltage to it. In either case, you need to study as Martin suggested. Don't get wrapped up in measuring ohms and playing with meters. You are not getting any info that will help you. The gas gauge readings are not real accurate on 99% of old trucks. Old technology and dirty meter movements, goofed up needle attachment, slosh, Loss of ground, Chinese float arm got bent a little during shipment. There is a lot of possible mechanical variation between float and rheostat wiper. Between wiper and rheostat coil range.
At the meter movement: Between magnets, pivots and needle; and between needle sweep arc and hash marks on gauge face. Lots of large tolerances.

Take out the gauge, get new sender, wire it up properly on the bench and move the arm up and down. Report what you see before going any further. Member DADS50 has (had) a VID on here on how to bench-wire the components and test them. Maybe DADS50 can repost the information because it got lost during various "upgrades/versions/non supported software" somewhere along the line. https://www.stovebolt.com/ubbthread...er/750427/Searchpage/1/Main/109807/Words

Continuing to maintain positive ground makes no sense. It will lead to mistakes by you and anyone trying to help you. EVERYTHING, EVERY part you buy is marked for Neg ground. ALL instructions are for Neg ground.

NOTE 1: Most gauge bodies/gauge frames need to be grounded. This ground, if necessary, is hard to achieve and maintain. Many gauges have a "lug" on the back. That is supposed to touch cluster metal. Cluster touches dash metal and so on..........back to the battery. A torturous path relying somewhat on just intimate contact, maybe a few sheet metal fasteners.

NOTE 2: The sending unit needs to be grounded by attaching a wire to one of it's flange screws and then to bare metal spot on frame.
NOTE 3. Always nice to know make model year of vehicle.
NOTE 4. Be careful making statements like "grounds are good". The approach for trouble shooting is to be pessimistic, not optimistic, because something is wrong and you don't know what. So everything is on the "person of interest" list.

Note to all future tank and gauge replacers:
You must assemble the components on the bench and test them together BEFORE installing. This area comes up many times as Martin said. You MUST establish a base line/boiler plate system on the bench and move the float arm up and down to observe If it works, how accurate it is, if it needs needle tweak, better grounds, compatibility, bad new parts, etc. Some folks will "calibrate" the set on the bench for accuracy. The gauge and the sender are some of the most difficult components to reach and test after they are installed. Knowing they work is a good advantage later on and saves your back, your knees, your neck and your butt.

Bartamos I thank you very much for the recommendations/comments and all the other folks who provided there experiences and comments. The new sending unit arrived
yesterday. I had not signed in since my last message so did not see your message before installing the sending unit. All is well!! The gauge is indicating a bit less than half
full. I filled the new tank with 10 gallons and drove the truck about an hour after so less than half seems reasonable. My truck is a '53 GMC with a hydra matic transmission.
The truck, except for the frame and running gear was totally dis-assembled but I bought it hoping that all the pieces were there, which most were.To re-assemble the truck
I relied on resource's like Stovebolt & internet but mostly the Maintenance Manual for GMC Trucks. I mention this because all new wiring was required. The manual's wiring
schematic specified the ground be on the positive pole. So with all electrical now functioning as expected I would be hesitant to change the ground to positive.

When this all started I had some concern that the fuel gauge was the problem. A few years ago the starter was not engaging which required me to nudge the crank a few
degrees to engage. I entered a post about the pros and cons of converting to 8 volt, the responses were many, probably more cons than pros and some pretty emphatic that
making the change was just a disaster waiting to happen. Well I made the change anyway so wondered if that was my problem. When I ordered the sending unit from Jim
Carter I asked if that might be the problem. Their response was that no it should not be a problem. They had done some research on the subject and found that in that
time frame a truck could be ordered with an 8 volt battery. Makes my mind a little more at ease but it is no guarantee that something may fail down the road.

Great news. great attitude. We all must filter the info received. Weigh the preponderance and reason it out. I do that on every issue I get into. We all try to give our opinion, experience, theories, guesses and offer testing procedures. It's a lot to cypher. You get it. You did it. These posts live on as part of the database.