Hi all-

I have a 2006 F-350 Superduty Diesel. I have noticed that (for example) when I park my truck at home my fuel gauge will read, say 3/4 tank, then when I park my truck at work which is at a slight incline, at the end of my shift when I start my truck up it will read 1/4 tank, but......it will continue reading 1/4 tank until I start the truck up again, or until it has had some considerable time sitting on level ground. Why is the recovery time so long? Shouldn't the reading on the gauge be instantanious as to the level of fuel is in the tank at any given incline. I realize that at an incline the gauge is going to read differently than if the truck were sitting level, it just doesn't seem right that the gauge takes so long to reflect that. Hope that made sense. And again, thanks for any input.

 

Might have something to do with 'key on/cycling' times if sitting or parked..Slosh mode...


Fuel Gauge
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 low (15 ohms ± 2 ohms). When the fuel level is high, the resistance in the unit is high (160 ohms ± 4 ohms).
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 uses 4 different operating modes to calculate the fuel level:
· 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 when refueling 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) (automatic transmissions), or the parking brake applied (manual transmissions).
· 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) or when the parking brake is applied (manual 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) or the parking brake is released, 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.

 

Thanks again-

I had no idea it was such a techincal matter. So now that I understand it a little better, I won't concern myself about it so much. Seems like it's working the way it should and nothing is wrong after all.

Thanks!!