Fuel Guage reading randomly

[darren_mk]

Hi all,

I have used the search function, but cannot come up with an answer to my problem:

1989 325i -

when tank is nearly empty, you put £20 quids worth in, then the guage reads 1/2 full!! It then will settle during a drive to around 1/4, but then start reading 1/2 full again. Then it will go all the way down to reading near empty after a few days. It seems to have a mind of its own.

I have tested both senders and they seem ok, (not exactly sure what resistance they should read) but they have no significant fault, the resistance changes when the float moves up and down the sender.
When you bridge the cars wiring in stages, i can make the light come on, make the guage read half, and make the guage read full.
The instruments are known good, so the fault must be either in a sender or the cars wiring?

The only other issue is that the tank has suffered some 'contact' damage with a ditch, so could this have caused any collapse of any baffles inside it causing the guage to read badly?
If not then where do i go from here?

[Brianmoooore]

Try shorting out the wires to one of the senders at a time when you have less than half a tank of fuel on board. This will give an inaccurate reading on the gauge, but if you get a steady reading, the faulty sender is the one that's shorted out.
No baffles inside the tank to come loose. Just a cup that the fuel pump intake sits in.

[Grrrmachine]

http://www.e30zone.net/e30zonewiki/inde ... el_Senders

[darren_mk]

Ok Brian heres the results, ignore my previous info - this is whats happening:


LHS is the sender with fuel pump
RHS is the sender on its own.

I cannot guarantee there is less than 1/2 a tank as the guage dosent work! - but would be 99% sure.

LHS Bridged and RHS Bridged = Guage reads full
LHS Connected and RHS Connected = Guage reads zero
LHS Bridged and RHS Connected = 1/4 Full on Guage
LHS Connected and RHS Bridged = 1/8 Full on Guage

Obviously the orange light will come on when you bridge that wire.

[darren_mk]

Can anyone shead more light on my fault, based on the info above?

Brian, whats the significance of having less than half a tank when doing the test?

[redcar]

Mine does something similar to this

I think its a combination of changes in gradients and the nature of the e30 system.

The gauge moves very slowly when i have a full tank but then moves very fast after 1/2

[darren_mk]

Thanks Willnz,

Thing are starting to make sense now!

I think i may have an issue with this syphon, as i can only see fuel in the lhs of the tank. When i remove the rhs sender the tank is dry!!
Should both sides have the same amount of fuel in them at all times?