How does the fuel gauge work?

[fsSnowboard]

Mine fuel gauge isn't working i don't think. I just filled my front tank. For starters, my gauge said it was low and i only put 10 gallons in, when normally i put 12-14 (i know its supposed to be an 18 gallon tank). I left my rear empty. I'm going to fill my rear tomorrow maybe to see if it is the tank selector switch that isn't working. But anyways, how does the fuel gauge work? would a slight air leak at the electric fuel pump mess up its readings? i discovered that i have some slight seepage from either the front of the electric pump where my fitting connects to the pump or from the bottom plate on the pump. BTW, is there anything better to seal than Teflon tape?

i'm just feeling a bit depressed. I accidentally left my lights on today at work so had to have them charged this evening. anyways, i hope it made sense.

 

[subway]

the reader in the tank is a variable resister and the fuel gage itself is basically an ohm meter. the float changes the amount of ground that the guage sees which in turn should show the amount of fuel you have. i dont remember what the readings should be for a full tank versus a empty one but you could check that at the tank without the wiring to make sure the sender is good. then work back form there up the wiring to find the problem.

unless the pump is some how not grounded properly it should have no effect what so ever on the sending units reading. they should be electrically seperated form each other.

i agree you should try filling the rear to see if it could be your switch before you really start tearing into it.

dont know of anything better than teflon, might just have to re-do the connection with some more teflon. make sure you wrap against the thread so it dousent just come undone as you tighten it

 

[typ4]

NEVER use teflon tape in a fuel stytem, I know I am going to catch h over this but I have taken apart lots of diesel fuel systems and found little strands of white stuff in the pump and injectors.
They will raise cain with the close tolerances in there.
Saw a new perkins get toasted because the pump hung open somehow things fly a long ways at what I estimated to be 6k rpm's, I was running towards it to shut it down when it let go. Took the pump back to the rebuilder and he was fully prepared to buy a new engine till he showed me the tape strings and the card in every box he sends out that says NO teflon tape, we should hire mechanics in LA that read english I guess. Anyway he recommended permatex, the brown gunk that we all know and love and said use any sealer sparingly.
I double checked with my local guy who I trust with all my fuel stuff and he concurred.
There is my experience fwiw.
russ

 

[subway]

wow thanks for the heads up, that is good information to know. i can see that happening but if you are working with the fuel pump any off that crap should get caught in the filter. i think after the filter you could be asking for trouble though.

any update on the truck Tyler?

 

[Agnem]

I use that teflon paste. Seems to work just as good, but it's a little messy.

 

[typ4]

paste is good

 

[fsSnowboard]

sorry, i thought i updated yesterday. i filled up the rear tank and its my front sending unit that is out. the rear seems to be working fine. I think I'll go find some permatex and try that out because I'm pretty sure I'm getting seepage through the threads on the fitting. anyways, I'm feeling better and was just having a bad night.

how hard is it to work work on the sending unit? i'm not able to pull off the bed to do any work on the tank.

Thanks for the responses guys.

 

[subway]

to work on the sending unit you are either going to have to lift the bed or drop the tank. there isent enough room to lift the sending unit out while the tanks is in place. of course you could just hole saw a big acess hole over the sending unit in the bed and work on it from there. i have see that before, ugly but handy.

i would check the sending unit with an ohm meter before dropping the tank with the wires disconnected to rule out a bad connection. with the tank full from what i have found the readings should be 158 ohms verses 16 ohms empty (found http://hp.autometer.com/techtips/faq_tech_writeups/fuellevel/fuellevel.html so feel free to correct me if i am wrong). i would hate to see you pull the tank for a loose connection.

good luck

 

[adrianspeeder]

I've found it easier to pull the bed than to drop the tanks.

Adrianspeeder

 

[highest_vision]

to work on the sending unit you are either going to have to lift the bed or drop the tank. there isent enough room to lift the sending unit out while the tanks is in place.

I put the sending unit in my front tank without pulling the bed or dropping the tank Wasn't too bad. I HIGHLY reccommend getting a new sender retainer ring.
James

 

[typ4]

Put some never seez on those retaining rings and they will almost fall in, well you know what I mean.

 

[icanfixall]

The front tank sending unit can easily be pulled without the dropping of the tank or lifting the bed. Get under the truck and have a look see. Just remove the wires, lines and knock the ring loose. Then pull it up and out. Thats all there is to it. When going back in there is a grove that must be lined up before things set properly. Clean things off because of the dirt that is sitting on top of the sending unit. Sure, the filter will catch it but why put it in the filter. They are expensive....

 

[highest_vision]

When I have done it under the bed, the ring has distorted They don't work too well after being straightened out either but when you don't have an extra just in case, you just do what you have to.
Oh, if it doesn't go in right, the tank will leak
I also will admit that I used to be unfamiliar with antisieze . Unfortunately it wouldn't have helped here though.
James

 

[fsSnowboard]

hey thanks for the help, this will probably wait for a while untill i'm able to remove the bed. would a sending unit that is going out incorrectly measure my rear tank. the gauge says half a tank for 50 miles but i'm pretty sure I havn't used that much fuel. when i filled it up it was on E and i only put 10 gallons in it.

 

[Squirreltow]

the reader in the tank is a variable resister and the fuel gage itself is basically an ohm meter. the float changes the amount of ground that the guage sees which in turn should show the amount of fuel you have. i dont remember what the readings should be for a full tank versus a empty one but you could check that at the tank without the wiring to make sure the sender is good. then work back form there up the wiring to find the problem.

If the sending unit tests out fine, but the fuel gauge reads over the top, would this be a short in the wiring? Yellow or Black any ideas?