Fuel tanks reading full
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Senior User
Joined: Dec 2013
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From: Lockport
Fuel tanks reading full
Okay, so I have been trying to search through and find something to directly help me. I have found a lot on the issue I am having, but the truck has me banging my head against the wall at this point and didn't know if someone could direct me more readily.
Now that I have ranted...
I am working on an 1988 F250 4wd 460 efi.
When I was driving the truck home after buying the rig I filled the front tank and put some in the rear. While driving the tank never left full and the rear then went to full and both haven't budged since.
Should I be looking a into the dual function reservoir, sending units, or what? also both tanks run the truck with no issues.
I have the bed off currently too.
Now that I have ranted...
I am working on an 1988 F250 4wd 460 efi.
When I was driving the truck home after buying the rig I filled the front tank and put some in the rear. While driving the tank never left full and the rear then went to full and both haven't budged since.
Should I be looking a into the dual function reservoir, sending units, or what? also both tanks run the truck with no issues.
I have the bed off currently too.
Fleet Mechanic
Joined: Feb 2007
Posts: 1,652
Likes: 79
From: Mooresville, NC
Okay, so I have been trying to search through and find something to directly help me. I have found a lot on the issue I am having, but the truck has me banging my head against the wall at this point and didn't know if someone could direct me more readily.
Now that I have ranted...
I am working on an 1988 F250 4wd 460 efi.
When I was driving the truck home after buying the rig I filled the front tank and put some in the rear. While driving the tank never left full and the rear then went to full and both haven't budged since.
Should I be looking a into the dual function reservoir, sending units, or what? also both tanks run the truck with no issues.
I have the bed off currently too.
Now that I have ranted...
I am working on an 1988 F250 4wd 460 efi.
When I was driving the truck home after buying the rig I filled the front tank and put some in the rear. While driving the tank never left full and the rear then went to full and both haven't budged since.
Should I be looking a into the dual function reservoir, sending units, or what? also both tanks run the truck with no issues.
I have the bed off currently too.
I'd pull the sending units (floats), clean up the connections, add clean dielectric (as preventative maintenance) since you've got the bed off..........sooner or later they'll need it anyway.........then troubleshoot wiring, tank selector switch, etc.........
Cargo Master
Joined: Jul 2009
Posts: 2,541
Likes: 54
From: Des Moines
Okay, so I have been trying to search through and find something to directly help me. I have found a lot on the issue I am having, but the truck has me banging my head against the wall at this point and didn't know if someone could direct me more readily.
Now that I have ranted...
I am working on an 1988 F250 4wd 460 efi.
When I was driving the truck home after buying the rig I filled the front tank and put some in the rear. While driving the tank never left full and the rear then went to full and both haven't budged since.
Should I be looking a into the dual function reservoir, sending units, or what? also both tanks run the truck with no issues.
I have the bed off currently too.
Now that I have ranted...
I am working on an 1988 F250 4wd 460 efi.
When I was driving the truck home after buying the rig I filled the front tank and put some in the rear. While driving the tank never left full and the rear then went to full and both haven't budged since.
Should I be looking a into the dual function reservoir, sending units, or what? also both tanks run the truck with no issues.
I have the bed off currently too.
If the gauge is pegged to the full point for both tanks and you know at least one of them is not full, it's most likely a gauge problem, or a wiring problem between the sending units and the gauge. Check the grounds for your instrument cluster (I'm sorry but I don't know where they are on a 1988 - Subford can tell you) and if that's all good, trace the wiring from the gauge to the sending units and check connections along the way.
Without having a wiring diagram, one thing I can tell you is that 1 common point for both gauges is going to be the fuel tank selector switch - it's possible that failed.
Posting Guru
Joined: Jul 2011
Posts: 1,219
Likes: 2
From: Elk City, OK
So what could be the cause of it reading full all the time? Mine has the same problem
Fleet Owner
Joined: Aug 2005
Posts: 23,667
Likes: 301
From: Easton,Ks
Most of the time there is a buildup on the resistive element of the gauge sender making for an open circuit.
High resistance means the gauge reads full or an open pegs the gauge passed full as in the wiper not making contact with the resistive element or an open wire.
The photos below are from the 90's type gauge sender but 88 sender works the same way.
The resistive element:
The parts:
/
High resistance means the gauge reads full or an open pegs the gauge passed full as in the wiper not making contact with the resistive element or an open wire.
The photos below are from the 90's type gauge sender but 88 sender works the same way.
The resistive element:
The parts:
/
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Senior User
Joined: Dec 2013
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From: Lockport
Awesome, I am going to try the sending units today... weather permitting.
If it is the tank selector how do I go about testing that?
If it is the tank selector how do I go about testing that?
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Elder User
Joined: Mar 2014
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From: St Charles Missouri
U mean how to test if the tank is actually working and just the guage is not? If that is what you mean, I just got to a quiet place, flipped the switch to the tank that the guage was not working and put my hand on the tank to try to see if I could hear or feel the pump start to work
Fleet Mechanic
Joined: Feb 2007
Posts: 1,652
Likes: 79
From: Mooresville, NC
Before diving in that deeply, are you sure you don't have an OPEN in your circuit heading from the sending unit(s) up thru the selector switch up to the fuel gauge..........an OPEN in this circuit would give FULL readings from both tanks.......
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Senior User
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From: Lockport
I just want to thank you guys and all the helpful info.
I tested the sending units' pigtails by closing the circuit with a wire; both tanks then read empty. (little bit more redneck than with an actual ohmmeter, but works) I double checked by plugging in a new sending unit just into the pigtail and was able to move the gauge with moving the float by hand.
I swapped both sending units and both gauges are in working order.
Sadly I don't have magic tanks that stay full anymore... then again with the 460 I don't think they will ever really be full.
Thanks again
I tested the sending units' pigtails by closing the circuit with a wire; both tanks then read empty. (little bit more redneck than with an actual ohmmeter, but works) I double checked by plugging in a new sending unit just into the pigtail and was able to move the gauge with moving the float by hand.
I swapped both sending units and both gauges are in working order.
Sadly I don't have magic tanks that stay full anymore... then again with the 460 I don't think they will ever really be full.
Thanks again
Elder User
Joined: Mar 2014
Posts: 648
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From: St Charles Missouri
^ cool man so do you have to take off the bed and drop the tank to replace the sending unit or is this something you can do w/ the bed and tank still on? I probably need to do this too. Right now I put 5 gal in the rear and reset the trip odo to 0 and I know I can drive at least 65 miles or so lol. My front tank is kinda screwy too but it "seems" to work
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Senior User
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From: Lockport
I already had the bed off. I was painting the frame and the bottom of the bed with bed liner. It is going to be a work truck and is way to pretty to let rust away.
I think taking the bed off may be over-kill if you don't have another reason, but it made it the easiest fuel pumps I have ever replaced.
You will have to drop the tanks to do the front sending unit. if the rear is empty you may be able to get away with only dropping it slightly. but dropping them all the way out isn't crazy difficult.
I think taking the bed off may be over-kill if you don't have another reason, but it made it the easiest fuel pumps I have ever replaced.
You will have to drop the tanks to do the front sending unit. if the rear is empty you may be able to get away with only dropping it slightly. but dropping them all the way out isn't crazy difficult.
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