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Gas gauge while filling

 
Old 02-10-2019, 11:52 AM
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CSixDude
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Default Gas gauge while filling

Has anyone ever observed the gas gauges behavior while the car is being filled? If so, did you notice that it will stall out at just below the half tank mark and not move, and then start moving again right before you get it nearly full? Just wondering if this is normal behavior or not.

Gage operates normally when driving and drops progressively through out its entire range as it should. I only notice this when filling if I leave the ignition on and observe the gauge.

Last edited by CSixDude; 02-10-2019 at 11:54 AM.
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Old 02-10-2019, 11:57 AM
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Oh Boy
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Mine operates the exact same way. Guess it takes time to catch up once the first tank is fulled and the second one starts catching up. Just my 2 cents.

Last edited by Oh Boy; 02-10-2019 at 11:57 AM.
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Old 02-10-2019, 12:02 PM
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FAUEE
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Pretty sure my gas gauge doesnt function with the car off, and having the car off is literally the first rule posted at the gas station.
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Old 02-10-2019, 12:07 PM
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CSixDude
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Originally Posted by FAUEE View Post
Pretty sure my gas gauge doesnt function with the car off, and having the car off is literally the first rule posted at the gas station.
Understood and I don't make a habit of this, but I recently had to replace my fuel sender unit, and I need to know its working properly.
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Old 02-10-2019, 03:28 PM
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owc6
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You could put the car in service mode in order to see this w/o the danger of fueling while the engine is running.

Make sure you exit this mode, however, because the car will NOT time out and go to sleep.
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Old 02-10-2019, 04:59 PM
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Normal. When the car is running and driving the car draws down the right tank first, then the left. So, for instance when you see half a tank on the gauge it's empty on the right and full on the left. The BCM interpolates it for you. Remember now, the fill is on the left. When you fill the car the gas goes into the left tank and flows over to the right. While you're filling and the gas is flowing across the tanks the fuel levels are momentarily not what the BCM expects and it gets confused because it is seeing fuel levels that it wouldn't ordinarily see under normal operation. As soon as it is full or you start the engine (energise the pump) the fuel flows where it belongs and the gauge shows as it should.
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Old 02-10-2019, 05:26 PM
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Thanks, it sounds like it's normal so I won't worry about it. I was afraid that the sending unit arm was getting hung up on something when filling,because it would stall out at just below the half tank level and stay there, and then it starts moving again just prior to it getting full.
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Old 02-10-2019, 08:29 PM
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Originally Posted by Sox-Fan View Post
Normal. When the car is running and driving the car draws down the right tank first, then the left. So, for instance when you see half a tank on the gauge it's empty on the right and full on the left. The BCM interpolates it for you. Remember now, the fill is on the left. When you fill the car the gas goes into the left tank and flows over to the right. While you're filling and the gas is flowing across the tanks the fuel levels are momentarily not what the BCM expects and it gets confused because it is seeing fuel levels that it wouldn't ordinarily see under normal operation. As soon as it is full or you start the engine (energise the pump) the fuel flows where it belongs and the gauge shows as it should.
I thought the tanks always balanced out for equal weight distribution. Meaning there is always the same amount of gas in each tank. When the car is full and as the right tank is draining doesn't gas from the left tank start going over to the right tank. I mean that would make sense.
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Old 02-10-2019, 08:37 PM
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Originally Posted by Oh Boy View Post
I thought the tanks always balanced out for equal weight distribution. Meaning there is always the same amount of gas in each tank. When the car is full and as the right tank is draining doesn't gas from the left tank start going over to the right tank. I mean that would make sense.
Maybe it makes sense, maybe not, but that is incorrect. C5,6 do not work that way. Right tank is used first, then left.

The car has one fuel line, it runs off the left tank. It has one electric fuel pump, also on the left. On the right is a venturi pump that just feeds fuel from the right tank into the left, emptying the right and keeping the left full as long as there is fuel in the right tank to push over to the left..
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Old 02-10-2019, 08:44 PM
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From what I understand, and I am not an expert (one will be along shortly to correct/expound on my info), when fueling, the DS tank fills up, and when it reaches the Venturi siphon on the top, it then siphons into the PS tank (where the fuel level sensor is) as you continue filling.

It then uses all (or most) of the fuel in the PS tank first, then uses the DS tank for the last 9 gallons. It does not empty equally ( they fixed this in the C7 gen with a jet-siphon to equalize weight distribution).

Venturi siphons only work when there is enough fluid level to push up the "cap." This is why they work when fueling, but I don't see how this same siphon would work in reverse.
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Old 02-10-2019, 08:44 PM
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Never had the need to check it. Fill it and drive off.
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Old 02-10-2019, 11:26 PM
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Originally Posted by saplumr View Post
Never had the need to check it. Fill it and drive off.
I'm too worried about my windshield washer fluid warning light coming on then how/why the gas gauge operates while refueling.
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Old 02-11-2019, 04:35 PM
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dr_gallup
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Originally Posted by Sox-Fan View Post
When the car is running and driving the car draws down the right tank first, then the left. So, for instance when you see half a tank on the gauge it's empty on the right and full on the left.
Wonder why they decided to empty the right first? Seems like the weight balance would be better if it drew down the left side first since there's always a driver on the left and rather infrequently a passenger on the right. Must be a NASCAR setup.
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Old 02-11-2019, 08:11 PM
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CSixDude
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Originally Posted by owc6 View Post
From what I understand, and I am not an expert (one will be along shortly to correct/expound on my info), when fueling, the DS tank fills up, and when it reaches the Venturi siphon on the top, it then siphons into the PS tank (where the fuel level sensor is) as you continue filling.

It then uses all (or most) of the fuel in the PS tank first, then uses the DS tank for the last 9 gallons. It does not empty equally ( they fixed this in the C7 gen with a jet-siphon to equalize weight distribution).

Venturi siphons only work when there is enough fluid level to push up the "cap." This is why they work when fueling, but I don't see how this same siphon would work in reverse.
I think that when you are filling the tanks, once the left tank is full, the fuel passes from the drivers side to the passenger tank via the large diameter crossover tube. I believe this is the whole purpose of the large crossover tube. The two smaller lines that are inside the crossover tube are what connect to the venturi pump in the passenger tank, and this is how the fuel is extracted from the passenger tank when driving.

There is a very good explanation of how the system operates here -> http://www.corvetteactioncenter.com/...ystem-389.html





Last edited by CSixDude; 02-11-2019 at 08:25 PM.
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