fuel tank sender unit problems

[runnin4life]

hi
i have a problem with my fuel guage works about 10% of the time
now i think it is the part in the tank the sender unit? or is it the float?
any way i cant see my self getting one from the wreckers and had trouble getting a nos or after market one

what the deal with these things can i get a universal on to fit
or do i just find a car with a tank of similiar size and mod the tank so it fits


EDIT : discovered rocking the car make the guage move but as soon as you stop rocking it goes back to empty

[mistaboz]

Tried pulling the tank out to see if the sender unit and float are accessible? Might be a problem with your float...

[ZOOK60]

you will have too pull the tank out. The sender is removable just get another one from the wreckers.

[V8Patrol]

3 things cause a fuel sender to read wrong or not at all.......

A/ bad earth.......
Corroded earth mounts are the usual problem here.

B/ damaged float .....
back in the days when floats were made from brass this was a common thing but most floats these dasy are neoprane and their floatation charactistics never really fail.

C/ damaged resistance coil ....
Most likely its this part of the sender that has failed.
A quick description ...... the float arm has an "electrical contact point" near the hinge of the float, this contact point rubs against a thin wire that is wraped around an insulative board in a coiled fashion. As the float rises / falls the amount of electrical resistance through the coil alters.... the fuel guage then translates this resistance into a reading which we interprut as a fuel level.

What basically happens is that the wire is simply worn ouy over time and the electrical connection is then broken at a point leaving the guages ability to only read when there is contact with an area of the coil that is still working. Usually the coil breaks in the middle which means it will either read from full to half way or from half way to empty ( depending on how it is wired to read )

In some instances the coil gets moved around quite a lot and the individual wraps are often packed hard up against each other in one area thus leaving a single thread say in an area which normally has 5,6,7, etc threads. In this situation the fuel guage will become slow to move in the heavilly wraped area yet will rapidly respond in the area which is controled by the single lone thread.

My commodore has this problem. It reads "FULL" for bloody ages, then around 400Ks down the road it suddenly drops down to 1/4 and from then on reads normally for the fuel used till empty.

In the situation you have described I'd bet that the wire coil is damaged in either way described above ............ time for a run to the wreckers for a replacement sender unit


Kingy

p/s
if the pics option was working I'd post up a pic of a damaged sender unit for ya

[runnin4life]

time for a run to the wreckers for a replacement sender unit

thanks for that it helps alot i will drop the and and have a look

that was a great explenation what should i look for as a sign of wear ?
discouloring, or just it stands out

will check the earth and so on first
if i cant find a replacment at the wreckers
might be hard its a diahatsue F20

what could be my options get another sender unit from a tank of very similiar size and mod it to fit
not sure if thats possible

[V8Patrol]

Usually you'll see the wire coil damage easilly. The wire is only fine ( less than pubic hair thickness ) and the wrap of around 20 odd coils around the insulative board is generally around 30mm, so its easilly seen.

As for your "breed of rig", there will be other vehicles that use the same sender ....... example ..... my MQ Patrol has a Datsun 120Y fuel sender fitted in it !, so take your old unit with U to the wreckers.

Kingy