Gas guage not working

willbur283 · #1 09-27-2009, 11:54 PM

Hello everyone, i have a 2005 f150 supercab 4x4x lariat 5.4. The last time we towed the camper we had some sort of a feedback and blew several fuses in the truck. We were able to get the truck home and further investigation revealed that a wire in the harness in that runs on the driver's side frame rail was melted to several others. This harness carries the wiring for the tail lights, fuel pump power and sending unit, and trailer wiring. I disassembled the harness, removed it from the truck and repaired the melted wires. The solid black wire in the harness was the culprit. It melted the fuel pump sending unit wires and several others. I have repaired the wires and all wire check out ok. I have put an ohm meter across the sending unit and get a reading of about 5 to 85 ohms while moving the sending unit lever. I have confirmed that i have 12 volts going to the sending unit. But, i am also getting 12 volts back from the sending unit????? So, is the sending unit toast?!? Does anyone have any other ideas???

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SSCULLY · #2 09-28-2009, 12:18 AM

The resistance of the fuel sender is :

Flex Fuel
- Low 7 ohms +/- 2 ohms
- High 138 ohms +/- 2 ohms

Non Flex Fuel
- Low 15 ohms +/- 2 ohms
- High 160 ohms +/- 2 ohms

Try the DTM HEC and see what the fuel sending unit gives as the current info

With the key in the off position, press and hold the RESET and SETUP buttons, and turn the key to the run position, holding the buttons until TEST is in the display.

press the RESET button to scroll through the options.

The one you want to check :
F A/D : Fuel Level A/D ###
- This is the Analog / Digital ratio in a decimal number. The cluster will also display the level.

FUEL P ### this is the fuel level in a percentage.

willbur283 · #3 09-28-2009, 12:30 PM

I have not checked the ohm readings yet but I did perform the test.
The A/D 255
The fuel 255

I ran across a diagonstic screen that gave the following codes:
D900
9204
E013
D950
9201

Next!?!??

SSCULLY · #4 09-28-2009, 12:42 PM

That shows a problem with the fuel level sending unit

From the DTM section on Fuel A/D :

Quote:

FUEL
Displays the code (0-255) for the fuel sender input to the HEC. The fuel gauge will display a filtered fuel level value. This filter will keep the pointer from moving suddenly or erratically.
255 open send +/- 0
232 full stop +/- 0
215 Full mark +/- 10
178 3/4 mark +/- 8
138 1/2 mark +/- 7
93 1/4 mark +/- 5
41 E mark +/- 4
54 Low Fuel (0-59)
0-18 short (0-20 max)

willbur283 · #5 09-28-2009, 12:48 PM

So, I need to replace the fuel sending unit?

SSCULLY · #6 09-28-2009, 12:56 PM

That is my take from what the service manual, and the DTM from yoru truck are telling me.

The resistance seems off and the reporting from it says open ( more than full ).

What is the fuel level in the truck at the moment ?

You say you have fixed the harness correctly, and you get 12V back, which does not sound correct.

willbur283 · #7 09-28-2009, 01:18 PM

According to my readings I have 12 volts going out to the sending unit on the Black/Orange and returning on the Yellow/White. I found this by cutting the two wires. I hten measured the voltage coming from the "truck". I completely seperated the to wires to in a process of elimination. I wanted to know if there was any voltage coming from the truck going to the sending unit. I then chose a good ground and measured. That is how I know the Black/Orange is sending the voltage out to the sending unit. After finding the this I connected the black / orange and left the yellow/white open. I then measured the voltage to ground on the yellow/orange that is returning from the sending unit. I read 12 volts returning from the sending unit. I found the reading odd myself.??? Because I would think that the voltage should be less when going thru a resister. I know for a fact that the wires have been reapired correctly. I have checked continunity on each wire to verify. I just hope that replacing the sending unit will fix the issue. I hope that it is not something like replacing a computer module.

willbur283 · #8 09-28-2009, 01:20 PM

At the moment the level in the tank is very close to empty. I am doing good to 2-3 gallons in it.

willbur283 · #9 10-07-2009, 12:14 PM

OK after testing the resistance on an empty tank I get 23.7 ohms. On a FULL tank I get 174.7 ohms.
FUEL
Displays the code (0-255) for the fuel sender input to the HEC. The fuel gauge will display a filtered fuel level value. This filter will keep the pointer from moving suddenly or erratically.
255 open send +/- 0
232 full stop +/- 0
215 Full mark +/- 10
178 3/4 mark +/- 8
138 1/2 mark +/- 7
93 1/4 mark +/- 5
41 E mark +/- 4
54 Low Fuel (0-59)
0-18 short (0-20 max)

Also I have checked all of the fuses, none blown. When I go to start the truck the fuel guage is pointing directly at empty. After starting the guage goes BELOW empty and stays there?????

SSCULLY · #10 10-07-2009, 01:10 PM

Don't start a new thread each time, just use the existing thread you have going ( makes finding the info to date easier )

The AD fuel value from the HEC is not the resistance reading.

The resistance should be :
Flex Fuel
- Low 7 ohms +/- 2 ohms
- High 138 ohms +/- 2 ohms

Non Flex Fuel
- Low 15 ohms +/- 2 ohms
- High 160 ohms +/- 2 ohms

From your values you seem to have a bad fuel level gauge, did you replace that yet ?

willbur283 · #11 10-12-2009, 11:09 PM

Quote:

Originally Posted by SSCULLY

Don't start a new thread each time, just use the existing thread you have going ( makes finding the info to date easier )

The AD fuel value from the HEC is not the resistance reading.

The resistance should be :
Flex Fuel
- Low 7 ohms +/- 2 ohms
- High 138 ohms +/- 2 ohms

Non Flex Fuel
- Low 15 ohms +/- 2 ohms
- High 160 ohms +/- 2 ohms

From your values you seem to have a bad fuel level gauge, did you replace that yet ?

Do 2004 - 2008 fuel pumps for 5.4 L interchange?

willbur283 · #12 10-12-2009, 11:11 PM

Do 2004-2005 fuel pumps and level guages interchange? for 5.4L