Fuel Gauge Showing Less Than Correct Amount - S-10 Forum
 
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post #1 of 10 Old 12-27-2015, 08:04 PM Thread Starter
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Fuel Gauge Showing Less Than Correct Amount

Hi all. My first post! Wow!
I apologize ahead of time, but I'm not quite sure what section this belongs in.

I have a 1986 S-10 pickup 2.8L V6.

Last week my gas gauge started acting wonky.
I was driving and noticed that it was on E. I thought I should have had more gas than that, but not knowing if I now had a leak in it, I filled it up.
It only took about $11 (figure about 3.5 gallons, 13 gallon tank, right?), but it now showed full. I thought that was weird, but hey, whatever. Anyway, I didn't pay any more attention to it til a couple days later.
I was driving and I happened to look at it and saw that it said that I had just a hair over 1/4 tank. I knew that was wrong because I did not have a leak.
So I'm driving down the road a few minutes later, and all of a sudden I notice it jump back up to a little over 3/4 tank (the correct level).

But a couple minutes later it drops back down to about 1/4 tank. Yesterday I started it up and it was showing the correct level again. for a couple miles. Then it dropped back down to a bit less than 1/4 tank (because I had used a little gas since the day before).
It seems to be showing the correct amount of gas USAGE, but not always the correct level.

I should mention that about 4-5 years ago, something happened inside the tank (someone said that a baffle that prevents sloshing movements probably came loose) and that now I get very small movements of the gauge caused by the gas moving around in it. Never had any problems with it though.

Also, I should mention that if I turn the key off, the gas gauge always stays where it was when running. But if I turn my lights on it drops down to E.
Also, if I turn my lights on while running, it drops down the smallest, smallest bit. It has done this for years. Never had any problems with that though either.

Anyway, taking a guess, I think my sender is probably OK, but I probably have a problem with the gauge or the wiring.
As you know, you can't get to the tank easily at all!

Would anyone have any thoughts or insight about this please. Thank you!

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post #2 of 10 Old 12-27-2015, 08:42 PM
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Re: Fuel Gauge Showing Less Than Correct Amount

Irratic fuel gauge is usually due to a bad/failing sending unit. There's very thin fingers that move back and forth as the float moves up and down. These eventually wear through, and cause false readings. Only way to know for sure is to pull the fuel pump assembly.

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post #3 of 10 Old 12-28-2015, 04:35 PM Thread Starter
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Re: Fuel Gauge Showing Less Than Correct Amount

Hi IHaveNoPantsOn! Thanks for the response.

I wish I knew for sure if it was the sender or not. Hate to have to go to all that trouble to get to the tank just to find out it was something else.

The thing that makes me think it's not the sender, is that it seems to be showing the correct usage of the fuel. According to info on the net, GM uses a 0-90 ohm resistance on it's sender, with 0 being empty, and 90 being a full tank.

If the sender was bad, how could it be going to LESS resistance periodically and then back to where it would be if if was showing the correct level. Usually, when a pot goes bad, it shows higher or infinite resistance (loss of contact connection), not less resistance.
That would be a short, which would be 0 ohms, which would equate to an empty tank, not around a quarter tank.
And if there was a bad ground, the resistance would be higher, showing more fuel in the tank, not less like it does now.

Any thoughts on that? Thanks.
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post #4 of 10 Old 12-28-2015, 08:24 PM
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Re: Fuel Gauge Showing Less Than Correct Amount

the ERRATIC operation comes from your Resistor bridge on the sending unit being worn flat over a majority of its span after many years of the wiper arm that runs across it wearing it down

Replace it

http://www.oreillyauto.com/site/c/se...S10&vi=5003084

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post #5 of 10 Old 12-29-2015, 12:52 PM
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Re: Fuel Gauge Showing Less Than Correct Amount

I've had the tiny wires on the sending unit burn up to where only half the time it would show fuel level, check that it's not hard to check


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post #6 of 10 Old 12-30-2015, 09:56 AM
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Re: Fuel Gauge Showing Less Than Correct Amount

Quote:
Originally Posted by etaomicron View Post
I've had the tiny wires on the sending unit burn up to where only half the time it would show fuel level, check that it's not hard to check
This is what I was talking about. You still have to pull the sending unit which requires dropping the tank (or easier) lifting the box off of the frame.

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post #7 of 10 Old 12-30-2015, 11:43 PM Thread Starter
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Re: Fuel Gauge Showing Less Than Correct Amount

Thanks etaomicron & Mad Max.

I guess after 30 years the sender could finally be bad.
I found one in stock at Autozone. Spectra Premium for $84. Bought it last night. I found a mechanic that will replace the sender for $110 in 2-3 hrs. After the beginning of the year. He's right down the street from my house. Too convenient. And a pretty good price too!
I am going to replace the sender for sure. I guess it's about time.
But before I do, I am going to temporarily hook up the new sender outside the tank to test my dash gauge while I move the float around. Hopefully only the sender is bad. I really don't feel like ripping my dash apart to get at the instrument cluster (f***). I've done it twice before. Once when I had to lube my speedo cable. And once when I replaced all my dash illumination with LEDs. It takes about 3 hrs start to finish just to take it apart and put it back together again.

I'll let you know the results. Thanks.
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post #8 of 10 Old 01-01-2016, 08:18 PM
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Re: Fuel Gauge Showing Less Than Correct Amount

Honestly I went ahead and put in a aftermarket fuel gauge and it's way more accurate. It's really easy because there's only 2 or 3 things that can go wrong with fuel level systems at least in our trucks


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post #9 of 10 Old 01-06-2016, 09:26 PM Thread Starter
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Re: Fuel Gauge Showing Less Than Correct Amount

Hi etaomicron and Mad Max.

I just had a new sender installed in my gas tank today. I had only a couple gallons in there to make it easy on the mechanic.
After it was installed, I went to the gas station and put in 4.5 gallons.
Same problem. My gauge shows that I have a hair less than 1/4 tank!
I know there should be almost 1/2 tank of gas!
The mechanic said that he grounded the gauge (like it was empty). Then he disconnected the signal wire to the sender (like it was full).
The gauge made full swings from empty to full just like it should.

I can only think that there is something wrong with the gauge itself.
I guess I'm going to have to rip my dash apart to try to see if I can fix the gauge.

I would sort of like to keep the original gauge in the dash as opposed to adding an aftermarket one somewhere.

Any thoughts??? Thanks.
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post #10 of 10 Old 01-07-2016, 09:40 AM
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Re: Fuel Gauge Showing Less Than Correct Amount

There's only a couple wires for the guage, I think it's pink or orange going to the tank, check every inch of it to make sure it's not broken. I put an aftermarket guage in my truck that ended up being way more accurate, but I'm sure you could find an oe gauge for it. Also take a meter and make sure the sending unit is operating in the correct range, 0-90 ohm I believe. If it's not the gauge and it's not the sending unit, it's gotta be wires to the gauge.


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