Sub Fuel Tank

Question edited to add year make and model.

The information is here by pinout, (pin 12)

http://orangecowboyhat.com/s10.html

https://www.google.com/search?q=98+s10+instrument+cluster+wiring+diagram

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Check fuse 4.

Chevrolet S-10 (1994-2004) fuses and relays

https://fuse-box.info > chevrolet > chevrolet-s-10-1994-...
1997 - Here you will find fuse box diagrams of Chevrolet S-10 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003 and 2004, get information about the ...


Wiring diagram for the fuel pump

https://www.google.com/search?q=1997+chevy+s10+fuel+pump+wiring+diagram&rlz=1C1QJDB_enCA643CA644&sxsrf=AOaemvIE_tX-Fl6Z8Z0iSxCsRVwqrIdvZA:1635212709552&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjP8byF-ubzAhV2nWoFHeZQCyEQ_AUoAXoECAEQAw&biw=1920&bih=937&dpr=1

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the gauge does what, (shoe drops) too high, tool low, or varies or smokes? lol "a problem tells nuttn"
the FSM is clear on the tests.
you check the 2 wires going tank sender say back end of car.
if tank full it can read, like 10 ohms or less.
and full like 100 ohms. Infinity is bad sender or wire to it.

i dont know how full your tank is.
if that test passes. the gauge is bad, lost power to gauge
ground to gauge broken or any where end to end tank to gauge.

the FSM covers this>?
best is to log in to
http://www.scantool.net/software/alldata-diy-1-month-subscription.html

alldata, and read. its all there, under fuel gage testing.

recap

1. bad fuse.
2. bad wire, bad connections end to end
3. bad sender
4. bag gauge.

quote , fsm on all 86's

1985 gauge test.
Trooper: remove the sub meter assembly and measure the resistance between the two terminals shown in the illustration. The resistance should be 25 ohms.

the gauge can be hot wired with say a 194 lamp in series
never do that , with no lamp. or you can smoke any gauge.
194 is a side lamp on millions of cars, top shelf of walmart elect, rack.(auto dept)


bingo?

my guess is the fuel sender is bad. in the tank.
did you check the resistance first?
low ohms say 25 full or over 100 empty
and NEVER infinity:?
yes/ no?
if it measures wrong , at the harness,
then its bad. or its conn, rusty.

so you must drop the tank on most cars to do this.

all this is covered in the FSM.
or all covered at alldata.com, log in read. (fuel system chapter)
ill answer for USA car, no engine options stated, (that too can change answers)
SUB 1500 , not 2500 answer. not stated that either.
4.3L ( of the 5 engines,)
ill quote the FSM (alldata page)
remove tank (sure drain it first.) the sender on this car is with pump assy.
1 Remove the fuel tank. Refer to Fuel Tank Replacement .
Remove the fuel sender assembly retaining ring using the J 44402 (Image 1) .

2 Remove the fuel sender assembly and the seal. Discard the seal.

Important: The fuel strainer must be in a horizontal position when the fuel sender is installed in the tank. When installing the fuel sender assembly, assure that the fuel strainer does not block full travel of the float arm.

see special tool to remove the assembly , clamp ring from tank.

buy the FSM
or login to alldata.com and read the instructions, warnings and all steps.
its non trivial.

but dont do it of the resistances read good.
first do the tests for the sender
and only replace it , if really bad.
why do all that work for 1min test..???/? <<< seen 10,000 times this forum. all guessing, sad to see.

Hi, Yes it is main tank fuel pump. need to replace.

ford have a gauge sender in the tank that operates by a resistance through the fuel. less fuel more resistance lower reading. I would check for voltage at the tank unit and it is more than likely the fault will be found in the sender unit

It could be either the switch is broken, pop it out and look for shorts or anything. The other thing that comes to mind is checking the fuel filter and fuel pump or the solenoid that switch between the tanks.

fuel gauges work using a variable resistor. Typically, when the fuel level is low, the fuel level sender is working at a high resistance. When the tank is full, the sender is working with a low resistance. Anything that increases the resistance in the circuitry will lead to a false low reading. Dirty or corroded wire terminals in the fuel sender circuit would raise the resistance. If you can remove the fuel sender unit from the tank, you can use an ohm meter to check its resistance. When the float is low, you should see a resistance of around 100 ohms. When the float is up (tank full) you should see a low resistance of about 2-5 ohms.

Hi this is a common problem the problem is going to be with the fuel sender unit located in the top of the main tank.

The problem is you might have to remove the tank to replace the broken part that is unless their is a panel in the boot that can be opened that allows you access to the top of the tank if not then you need to make sure you have used all the fuel in the main tank to ensure its empty as it would be really heavy if it had fuel left in it.

With tank empty its best if vehicle is on ramps as you need alot of clearance to get the tank out so just having it on jacks and axle stands wont give you enough room to get to the top of the tank.

You need to disconnect all the fuel lines ie the out line and the return line you also need to disconect the fuel filler hose from the fuel filler cap area. Once this is done you can then undo the tank brackets holding the tanks its best if you have something to support the tanks whilst doing this as its not a one person job once its all undone and you can start lowereing the tank check their are no air pipes being stretched if their is remove them but remember they need to go back on then once the tank is lowered far enough you will then see where the fuel sendor wires run to these will then need disconecting this should then allow you to remove the tank.

Once tank is removed the fuel sender unit is on the very top of the tank it can be undone it might be that the float is stuck or even full of fuel causing the empty reading.

You can test the fuel sender by just connecting the fuel sender unit back up to the electrics then switch ignition on then work the float up and down and see if the gauge alters on the dash if it does then the chances are it might work if you put it back in but if it dont its a wasted job.

Its best if you replace it as you might get the same problem in the near future.

If their is a panel in the boot then this makes the job easier.

Let me know how you get on or if you need further assistance ok

You don;t say whether the fuel gauge is reading accurately, or whether it's always on empty. If the gauge is always showing empty, it's most likely a problem with the sending unit in the fuel tank. Check the resistance across the two terminals of the sending unit.

On a C900, the fuel sender level unit is separate from the fuel pump and located on the right side top of the tank, accessible by removing the trunk floor lift up panel (the pump is located on the left side top of the tank.
Possible problems are: electrical line off or broken, float not working (it's fairly delicate); or gauge not working.

Test the resistance of the sending unit with the lines disconnected, the resistance should be 2.6 to 3.8 ohms full tank, 63.3 to 67.5 ohms empty tank; and test for voltage across the top of the sender unit, if no voltage, that's likely the problem!

If the gauge is otherwise reading accurately (showing 'full' for a full tank, etc) then the problem is likely a gauge malfunction and can be simply replaced.

Good luck!

Saabreur