M1008 fuel sender replaced???

[ssgtwright-usmc]

Today I finally replaced my fuel sending unit in my tank.
The old one that came out, the sock looked liked it was being used by McDonalds to filter their nasty deep fryiers.
The sock was like a brown stick of butter.
Anyways, I replaced the fuel sending unit, fuel gauge, replaced all rubber hoses, blew out the lines, cleaned the tank out and put in a new filter.

Now my problem is that the tank shows 1/4 full when the tank is full.
When I disconnect the ground to the sending unit then it shows full.
I am guessing its a grounding problem.
If so, what should I look for.
I looked at the TM and damn, looks like the sending wire goes to the gauge and also to the fuel filter electrical stuff.
Where can the ground be coming from.
The Fuel gauge is new, the sending unit is new, new rubber hoses, new filter and the line was blown clean.

Any idea where the ground might be coming from for it to show 1/4 tank when full now!
Thanks,
Tim

 

[ssgtwright-usmc]

OK, I replaced the sending wire and to no avail!
When the tank is full it is showing 1/3 full and it droped to 1/4 full which means 5 gallons between the two readings which is right for 60 miles of driving.
Is their a adjustment within the fuel gauge which needs to be adjusted or is their a short or ground somewhere?????
Please, My tank should not show 1/3 full with a full tank, anew sending unit and fuel gauge.
Any suggestion on this would be great.
Thanks,
Timothy Wright

 

[papercu]

The sending unit is a variable resistor that must have a good ground. The M1009 has a wire (at the tank) to ground, not sure about the M1008 but if it doesn't have a wire it would be grounded by the tank itself, but either way try a jumper to a known good ground to the wire or tank.
From the -20
29. FUEL GAGE INACCURATE

Step 1. Check 20 amp ignition fuse.
Replace if burned out.
CAUTION

DO NOT leave key in “RUN” position for more than 2 minutes. Failure to
may result in damage to glow plugs.

Step 2. Disconnect fuel tank sending unit ground from frame. Turn key to “RUN” position.
If fuel gage reads “F“ (Full), perform step 3.
If fuel gage does not read “F” (Full), replace fuel gage. (See paragraph 4-7)


Step 3. Disconnect pink fuel tank sending unit lead and touch lead to any ground.
If fuel gage reads “E“ (Empty), replace fuel tank sending unit,
paragraph 3-11 or 3-12)
If fuel gage does not read “E” (Empty), replace fuel gage.
paragraph 4-7)
BTW could you have bent the rod? Wayne

 

[corelokt]

To me it sounds as if the sending unit is not right for the truck. Did you hold the old and new side by side and compare? Were the arms the same angle, with the same amount of swing?

 

[ssgtwright-usmc]

The sending unit are indentical in everyway. Was carefull when replacing inside of tank.
I have a spare fuel gauge since that was the first thing I replaced hoping that would fix the problem.
Ill replace the gauge and see what happens after that.
The truck runs alot better with the new sending unit since it isnt clogged like the old one.

 

[Crash_AF]

Can you ohm out the old sending unit to see if it is working? If it is, then you should be able to disconnect the wires, hook them to the old unit (with a ground jumper) and then move the arm manually to see if the gauge moves properly. If not, you may need to trace the wires from the tank to the block on the firewall.

Later,
Joe

 

[ssgtwright-usmc]

Just replaced my fuel gauge with the one I originally took out.
Now looks like the gauge is now working.
Filled the tank back up and did the gas/milage usage and now it seems like Im getting better fuel milage with the new sending unit.
The old one, the sock looked like it sat in a chicken fryer for a few years.
I was getting 12 mpg and now Im getting 14.3 mpg.
Thats an extra 40 miles per tank now.
Now I have to do one more reading at my next fuel stop and do another reading to make sure.