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Fuel Gauge


Old 10-18-2007, 09:52 AM
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Join Date: Nov 2004
Location: Hagerstown, MD.
Posts: 25
Fuel Gauge

my fuel economy is reading 15.3 mpg on the computer. So on a 27 gallon tank I should get around 413 miles on a tank. Is there any way to calibrate the fuel gauge? I am only getting around 300 miles before I have to fill up and then I can only put in 20-22 gals. Any advice?
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Old 10-18-2007, 10:07 AM
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Join Date: Jun 2007
Location: upstate NY
Posts: 106
Not sure about calibrating. As far as the rest, I don't think you will ever run a vehicle empty enough to take the full capicity to fill it back up. Meaning, on a 27 gallon tank, it would be very hard to run it low enough to take 27 gallons without leaving yourself dead on the road. There will always be a few gallons in the tank.
i would suggest figuring your mileage by the miles/gallons method and see how far off the trip computer is. I'll post back later if I find out the display cna be calibrated.
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Old 10-19-2007, 02:17 AM
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Join Date: Nov 2006
Location: Memphis, TN 38135, USA, Earth
Posts: 5,492
On mechanical clusters, you can restab the needle onto the gauge shaft, but you have to KNOW how much gas is in the tank to get it right. That means running it dry, then putting a measured amount in before working on the needle.

On a HEC, I don't think it can be calibrated, other than by altering the sender circuit with resistors, but that's VERY technical.

Fuel Gauge

NOTE: It is critical to follow the pinpoint test diagnostic methods to make sure the correct mode is being used during diagnostics.

The instrument cluster receives the fuel level signal from the fuel level sensor, part of the fuel pump module. The fuel level sensor measures variable resistance in the fuel tank depending on the current fuel level. When the fuel level is low, the resistance in the unit is high (180 ohms 4 ohms). When the fuel level is high, the resistance in the unit is low (10 ohms 2 ohms).

The instrument cluster uses 4 different operating modes to calculate the fuel level:

anti-slosh (default mode)
key OFF fueling
key ON fueling
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 full (F) to empty (E).

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 when refueling the vehicle.
At least 15 percent 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 10 ohms 2 ohms and 180 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 percent 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. When the 30 second time has elapsed and at least 15 percent 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. This mode prevents slow to read full events from happening if the customer refuels the vehicle with the key in the RUN position.

Recovery mode is incorporated into the instrument cluster strategy to recover from a missing fuel level message during a refueling event. Missing fuel level messages result from intermittent opens in the fuel sender or its circuits. Recovery mode (empty [E] to full [F] approximately 20 minutes) is initiated when the following 2 conditions are met:

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.

Last edited by Steve83; 10-19-2007 at 02:25 AM.
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