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Old 04-22-2018, 06:14 PM   #1  
Hall1836
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Default Fuel gauge reading backwards?

Took the car out today and gas gauge was not working. It sweeps right to full then down to empty. Drove about 40 miles and gauge came off empty, two marks. As I continued to drive the needle moved closer to the full mark. It is now at the 3/4 empty mark, if it was working right I would be at about the 3/4 full mark. So it appears that as I burn fuel the needle is moving off empty to Full???
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Old 04-22-2018, 06:37 PM   #2  
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When starting, sweeping up and down is normal, but it will be interesting to see what everyone's take is on the creeping back up during the drive issue may be.

What's your fuel range reading during this?
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Old 04-22-2018, 06:40 PM   #3  
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Fuel range is working, range is dropping as fuel is burned.
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Old 04-23-2018, 01:19 AM   #4  
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A friend today was describing this same kind of reading on her C6. She got some codes indicating the passenger side gas float was faulty.

One can get a zero reading with a new tank of gas if the gas has too much sulphur. That usually goes away with the next tank of gas assuming it isn't as bad as the first tank.
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Old 04-23-2018, 06:30 AM   #5  
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I had the exact same problem with my C6. Look at the C6 forum and search in me as an OP or just search on fuel sending or sensing unit.

With the C6 the fuel sending unit in the passenger side gas tank (the one that drains first) would corrode over time. When the part first started to fail, after a fill up my fuel gauge would settle at empty until I burned about 1/2 gallon of gas. Then it was perfect.

However over time the behavior of the fuel gauge got worse and eventually became unusable. GM redesigned the part mid C6 and it was better but still failed (corroded) eventually.

Use only top tier gas, do not let your overall gas level fall below 1/2 (meaning there is still some gas in the passanger side tank) and use a good fuel system cleaner and maybe your issue will go away (assuming this is the same issue as with C6's).
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Old 04-23-2018, 08:04 AM   #6  
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Quote:
Originally Posted by Hall1836 View Post
Took the car out today and gas gauge was not working. It sweeps right to full then down to empty. Drove about 40 miles and gauge came off empty, two marks. As I continued to drive the needle moved closer to the full mark. It is now at the 3/4 empty mark, if it was working right I would be at about the 3/4 full mark. So it appears that as I burn fuel the needle is moving off empty to Full???

I would see if the behavior is consistent over the course of a few tanks of gas before taking it to the dealer. The more info you can give them, the better.

Fuel gauges, in general, are notoriously unreliable and their accuracy is rarely linear (i.e. it tends to be more accurate at one end of the gauge than the other). Sometimes it's just something stupid like you parked on a slope and the sender was slow to update the level on the gauge.
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Old 04-23-2018, 09:01 AM   #7  
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I don't know if GM Fuel System PLUS is the same thing but C6 owners with this issue have found that a can of Techron usually resolves it. Give it a try. If you’re not using Top Tier gas, you should be.
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Old 04-23-2018, 09:36 AM   #8  
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I put a bottle of injector cleaner in once a month.
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Old 04-23-2018, 10:10 AM   #9  
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I had a fuel gauge that would get "sticky" in an old Porsche 951/944 Turbo. A bottle of Techron in the tank usually "fixed" it for 3-5K miles. I know GM recommends only their brand of fuel additive, but I swear by the Chevron Techron additive - have been using it in my performance vehicles since the '90s.

Curious how these gasoline direct injection engines in the C7 react over time to carbon build up in the intake tract. I know in my wife's old Cadillac SRX with the 3.6L DI engine, they strongly recommended an intake cleaning every 30K miles. I saw the build-up for myself after dismissing it as a sales gimmick and swabbed the intake tract.

No intention of hijacking the thread - stick a bottle of Techron in there (get the larger bottle) and do some spirited driving until the tank's empty, curious if it fixes it for you!

Greg
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Old 04-23-2018, 12:15 PM   #10  
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Amazes me with some of these "back in the 80s/90s I did this---". We have come so far & yet some cannot embrace the BETTER technology. Maybe they're still running Windows 7? GM does recommend an additive (of course GM brand) if not able to find Top Tier detergent gasoline. Just having fun here.
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Old 04-23-2018, 01:06 PM   #11  
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Techron is good stuff.
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Old 04-23-2018, 04:29 PM   #12  
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"... yet some cannot embrace the BETTER technology."

It's only BETTER technology IF it works and works correctly consistently and on demand, while doing something important better. And, yeah, I still have perfectly good (for appropriate tasks) Windows 2000 and Windows XP machines but my notebook I'm working on from Starbucks is a W10. So...

Last edited by Avanti; 04-23-2018 at 04:33 PM.
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Old 04-23-2018, 05:09 PM   #13  
JerryU
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From past posts the problem may well be sulfur build-up on the sender!

On the C7 it is an expensive and scary fix! The rear drive train has to be removed to drop both tanks and the cross over! One poster was horrified when he saw his drivetrain on the garage floor!

Another poster said the dealer put in two bottles of the GM specified fuel additive that is says is to be used if you don't use Top Tier gas! He was charged $100. That solved his erratic fuel gauge reading.

What I Have Done and Am Now Doing:
Even though I mostly use Top Tier gas with my 2014 Z51 I added a bottle of the GM fuel additive every oil change. That is what the Owner's Manual says to do if not using Top Tier gas. However they stopped putting the GM number in the Owner's Manual and the old part number is no longer sold! Have to buy it from GM! Just changed the oil in my Grand Sport and added a bottle of Techron. Looking at the GM and Techron SDS (Safety Data Sheets) it looks to be the same "stuff." The bottle is also the same shape, I'd guess the GM stuff is made by Chevron who has the patent on Techron.

In fact Techron was what many gas companies use (or were using) to make Top Tier. If the bought from Chevron it included their patent royalty. Some have developed their own Top Tier additives to get around the patent.

You can buy Techron in a number of places, like Walmart, Amazon etc, discounted!

If I were the OP I'd sure try putting two bottles into a tank and see if it helps.

Sulfur in Oil:
Crude oil can contain ~3% sulfur! That is called sour crude. Sweet crude is more expensive and is in limited supply but still contains some sulfur. It is supposed to be mostly removed in refining.

Using Top Tier gas will provide a steady low level supply of Techron or the equivalent. The latest info for folks who store their cars for the winter is to fill the tank only 1/3 full to keep the fuel level sender out of the gasoline as it is mot moving around to help wash off any amount that coats the part!

This is what the bottles of both the GM product and Techron state:
ACDelco Fuel System Treatment states:
Your first line of defense against carbon build-up and sulfur in the fuel. Using ACDelco Fuel System Treatment Plus can also prevent fuel gauge malfunction by vanquishing deposits on the sending unit.

Techron States:
One treatment with TECHRON® Concentrate Plus can help:
* Clean corrosive sulfur deposits from fuel gauge sensors
* Restore operation of sulfur contaminated fuel gauge sensors

Last edited by JerryU; 04-23-2018 at 05:16 PM.
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Old 04-24-2018, 09:56 PM   #14  
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Thanks to all that responded, have added the Techtron and see what will happen. Stopped at the dealer today and they know nothing about adding a fuel additive? Those of you who have had this problem did the fuel gauge just bottom out and stay there? I can understand that being the problem, I'm stymied by the fact that the level goes up towards the full mark as I use gas, and drops to Empty when I fill up. Hope it's not something more complicated.
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Old 04-24-2018, 10:29 PM   #15  
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Quote:
Originally Posted by shakinrock View Post
I had the exact same problem with my C6. Look at the C6 forum and search in me as an OP or just search on fuel sending or sensing unit.

With the C6 the fuel sending unit in the passenger side gas tank (the one that drains first) would corrode over time. When the part first started to fail, after a fill up my fuel gauge would settle at empty until I burned about 1/2 gallon of gas. Then it was perfect.

However over time the behavior of the fuel gauge got worse and eventually became unusable. GM redesigned the part mid C6 and it was better but still failed (corroded) eventually.

Use only top tier gas, do not let your overall gas level fall below 1/2 (meaning there is still some gas in the passanger side tank) and use a good fuel system cleaner and maybe your issue will go away (assuming this is the same issue as with C6's).
This right here

You should let your gas tank go down periodically, at least to the pump station icon on the fuel meter. What that does is allow the sensor in the passenger tank to function. If the fuel levels never get to the gas pump icon, it tends to glitch out. I had this issue on my previous C6 GS. So, the moral of the story is to let the fuel gauge go down so that the passenger fuel tank sensor functions.

Last edited by SilverScorp; 04-24-2018 at 10:38 PM.
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Old 04-25-2018, 12:04 AM   #16  
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Techron Full Fuel System cleaner meets the same spec as the GM-specified additive. It is good stuff and widely available at almost any auto parts store. I use the specified dose every 3K miles or so as a preventative maintenance.
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Old 04-25-2018, 12:22 AM   #17  
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Quote:
Originally Posted by Hall1836 View Post
I'm stymied by the fact that the level goes up towards the full mark as I use gas, and drops to Empty when I fill up.
Not sure about the mechanism in the Vette but it may be the same as it has been for years. There is a float with an arm connected to the fuel level sensor. A wiper in the sensor moves over a strip of metal that changes resistance from the wiper to the end of the metal strip. If the section near the full area is coated with sulfur it will not make contact or the contact will be inconsistent. That could result in a no fuel reading.

Might add another bottle of Techron.
Curious, do you use Top Tier Gas?

Keep us posted.


The fuel sensor is located at the top of the tank. In my Street Rod I installed it and it is several inches below the upper fuel level.

Last edited by JerryU; 04-25-2018 at 12:32 AM.
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Old 05-03-2018, 08:40 PM   #18  
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Looks like the Techron did it's job, fuel gauge now working!
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Old 05-03-2018, 09:27 PM   #19  
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Glad that worked out for you.
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Old 05-03-2018, 09:37 PM   #20  
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Quote:
Originally Posted by Hall1836 View Post
Looks like the Techron did it's job, fuel gauge now working!
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