Fuel Level issues (Small)

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CharmfulPeace
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Fuel Level issues (Small)

Post by CharmfulPeace » Sun Jan 07, 2018 9:34 pm

Hey there, I have a quick question that I was wondering if any of you could help me with.

So first, I have to keep my tank under half due to an evap error (According to the code), but that is okay with me for the time being..
What I am wondering about is an issue I have with the float(? - Don't exactly know how fuel tanks sense levels) where it seems to drop quicker than it honestly should when I leave the car running for awhile.

So, I will know for a fact that I have just under half a tank, but it will show me that the level is well near or on empty.. If I turn the car off and leave her for a couple hours, the level will show as it should be instead of what it was showing prior to letting her sit.

Bare with me, as I am not the most car-savvy person (though I am trying to learn lol... Tech is more me.)
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2002 Chrysler Neon LE
1992 Honda Accord (Sold)
2004 Oldsmobile Alero GL (Sitting)
1992 Plymouth Acclaim (Sold)

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jonnymopar
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Re: Fuel Level issues (Small)

Post by jonnymopar » Sun Jan 07, 2018 10:41 pm

Curious, what is the evap code you're getting?
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Jon J.

2003 Neon SXT - 200k+ miles, still love it
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CharmfulPeace
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Re: Fuel Level issues (Small)

Post by CharmfulPeace » Sun Jan 07, 2018 11:03 pm

jonnymopar wrote:
Sun Jan 07, 2018 10:41 pm
Curious, what is the evap code you're getting?
Have to go off memory as it is now showing P1684 (Which I'm reading as PCM memory cleared since the last 50 ignition cycles), but, if I remember, the one that was showing up that read as an Evap Emissions control error was P0440.. Might have to fill it a bit over half again to get it to show up?

I did have it saved in an app on my android tablet, but I haven't used it in months and the screen ended up getting FUBAR'd so I would need to look at replacing it before I can open the app to see in the history.

(actually.. .P0440 doesn't sound right... )



***EDIT***
Okay! Just did a quick swap of the screen and can tell you that it was P0442 (Small Leak)
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2002 Chrysler Neon LE
1992 Honda Accord (Sold)
2004 Oldsmobile Alero GL (Sitting)
1992 Plymouth Acclaim (Sold)

occasional demons
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Re: Fuel Level issues (Small)

Post by occasional demons » Mon Jan 08, 2018 9:47 am

An evap leak has very little to do with retaining fuel in the tank, unless it happened to be the tank itself, but they are double layer, so I doubt the vacuum leak is from the fuel tank.

It could be the gas cap o-ring, a hose or other, but very rarely is it the tank.

With neons, the last half on the gauge always seems to drop faster.
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CharmfulPeace
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Re: Fuel Level issues (Small)

Post by CharmfulPeace » Mon Jan 08, 2018 10:55 am

occasional demons wrote:
Mon Jan 08, 2018 9:47 am
With neons, the last half on the gauge always seems to drop faster.
I know that, but it shouldn't be dropping from just under half to the point the fuel light comes on in a matter of a half hour or so, should it?

I know about quicker drops with the last half tank as I experienced that with my Alero also..

But when it drops to the point where the fuel light comes on, I stop and leave her sitting for an hour or so, and it will show it being back up near half where it should be.
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2002 Chrysler Neon LE
1992 Honda Accord (Sold)
2004 Oldsmobile Alero GL (Sitting)
1992 Plymouth Acclaim (Sold)

occasional demons
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Re: Fuel Level issues (Small)

Post by occasional demons » Mon Jan 08, 2018 11:45 am

Hmmm, could be corrosion somewhere, letting the resistance make it drop, but it doesn't explain why it comes back after leaving it off for a while.

Below is what happens with known good wiring, and how the gauge responds to keying off and back on. It might give some insight, but probably won't solve your issue.

Generally, if the sender circuit has an abrupt change in value, the gauge will not reflect that change. I know this from experimenting for other purposes. I had a resistor connected to a switch, so it would read as if the fuel were low enough to make the low fuel light flash.

Flipping the switch did essentially nothing, until you keyed off, and back on, then the gauge would rise to the low fuel level, and the low fuel light would flash.

But if the resistance is changing slowly enough,the gauge would register it. But what is changing to make it read "correctly" after sitting?

Unless the pump is heating up enough to affect the sender, and the time off lets it cool back down. But they are pretty well isolated from each other. The fuel would have to get warm enough to affect it. I think at that point, the pump might not live much longer, if it can heat ~6 gallons of fuel that much. If it were happening below 1/4 tank, I could see it, but a half tank?
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