# I have a 94 chevy s10 and my gas reads empty while i drive.but when i shut off the truck the gauge moves to different readings.

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Is......the problem--"the gas gage reads empty when there is fuel in the tank. OR, The gage moves when the key to turned off ?

If it's the first,
You will need to test the gage and through process of elimination, determin if the Sending unit inside the fuel tank has gone Bad.

If its the second ? - Electrical gauges will move when powered down. Normal

Testing the gauge may not be easy - just depends on your ability.
It is a simple 2-wire gauge circuit, when disconnect (usually need the fuel tank) the gage reads in one direction (either full or empty)
then when shorted-the gage reads in oppisite direction.

Of course you must select the correct wires or you may short out the wrong circuits!! Most GM vehicles use a purple wire & black wire.

A quick method I have used to check the in-take part of the gauge is this.
1st. know there is gas - 1/2 tank works best.
2nd driver's door open, key in run position, engine not running.
3rd gently lift up on the door then let if come back down, gently.
just enough to cause the gas to slosh around.
4th - keep an eye on the gas gage, a bad sending unit in the take will show up as a "twitchy" needle.

Of course, if the gage never leaves empty - sloshing won't work.
I have a known good sending unit I can plug into the vehicle and simulate different levels of fuel - if the gas gage works, I know the problem is in the tank.

Let us know.

Dave

Posted on Mar 13, 2009

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Shorted in tank sending unit. I personally have replaced over 200 of them. Dave Hamilton is correct in his advice . The newer gages won't always work like testing the old circuits. To properly test the fuel Gage itself you need a signal generator to send different amounts of resistance through the circuit. Just dis-connecting and then grounding the circuit won't work due to the fact that the ECM sees it as one thing and then converts it to another signal and sends it to the dash. MUD is right. Hope this helps. The sending units can be purchased without a fuel pump assy. so you can transfer it over. The tanks on these are really easy to do. If you have a splash shield , remove it. Take off the filler and return hoses. Disconnect the connector heading to the tank. Then with a deep socket take off the 2 straps and the tank will fall out. Try to empty the tank or drop it using a floor jack.

Posted on Jul 22, 2012

Hi,
a 6ya Mechanic can help you resolve that issue over the phone in a minute or two.
Best thing about this new service is that you are never placed on hold and get to talk to real repair professionals here in the US.
Goodluck!

Posted on Jan 02, 2017

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Anti-slosh (default mode)
Key OFF fueling
Key ON fueling
Recovery
After a fuel fill up, the time for the fuel gauge to move from empty (E) to full (F) ranges from 2 seconds to 55 minutes depending on which operating mode the fuel gauge is in.
The default fuel gauge mode is called the anti-slosh mode. To prevent fuel gauge changes from fuel slosh (gauge instability due to changes in fuel sender readings caused by fuel moving around in the tank), the fuel gauge takes approximately 55 minutes to go from empty (E) to full (F).
The key OFF fueling mode (2 seconds to read empty [E] to full [F]) requires 3 conditions be met:
The key must be in the OFF position throughout the entire refueling of the vehicle.
At least 15% of the vehicle's fuel capacity must be added to the fuel tank.
The instrument cluster must receive a valid key ON fuel sender reading within 1 second of the key being put into the RUN position. The key ON sample readings are considered valid if the fuel sender reading is between 15 ohms ± 2 ohms and 160 ohms ± 4 ohms.
If these conditions are not met, the fuel gauge stays in the anti-slosh mode, which results in a slow to read full (F) event.
The key ON fueling mode (approximately 90 seconds to read empty [E] to full [F]) requires 3 conditions be met:
The transmission is in PARK (P).
The key is in the RUN position.
At least 15% of the vehicle's fuel capacity must be added to the fuel tank.
In key ON fueling mode, a 30-second timer activates after the transmission is put into the PARK (P) position (automatic transmissions). When the 30-second time has elapsed and at least 15% of the vehicle's fuel capacity has been added, the fuel gauge response time is 90 seconds to read from empty (E) to full (F). When the transmission is shifted out of PARK (P), the fuel gauge strategy reverts to the anti-slosh mode. The key on refueling mode prevents slow to read full events from happening if the customer refuels the vehicle with the key in the RUN position.
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The instrument cluster is in the anti-slosh (default) mode.
The actual fuel level in the tank is greater than what is being displayed by the fuel gauge

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