BX Tank Sender

Unread post by **Jon** » 10 Oct 2004, 02:33

Anyone ever had a go at fixing one of these?
My fuel gauge swings between empty and 3/4, I've just put £30 of diesel in so 3/4 is probably about right, but the bloody gauge just sort of flickers about for most of the time, sometime even on a straight road!
The sender unit in the BX appears to be a cannister arrangement with some sort of coil inside, have not had time for a good lock at it as yet, does not seem to have plastic float arrangement like the ZX had.
Perhaps I just need to buy a new one, but, at £50.12 + vat........

Richard Gallagher · Unread post by **Richard Gallagher** » 10 Oct 2004, 03:01

The chances are that it is not the gauge or sender unit but the voltage stabiliser, a small sealed box usually found somewhere on the instrument panel. The purpose of this unit is to slow down the movement of the gauge needle, as the float moves up and down with the movement of the fuel.
I'm not sure about BX's but most cars do have such a device.

AndersDK · Unread post by **AndersDK** » 10 Oct 2004, 03:07

Hi Jon -
The sender unit is a dead simple slide potientiometer. My personal experience is that the 3pin multiplug fails, or the ribbon cable termination in the multiplug fails (corrosion).
The connections are as follows :
pin1 : earth feed
pin2 : lo (earth) side of gauge (resistor element)
pin3 : lo (earth) side of empty lamp (earth switch)
You'll find the plug under the center most large plastic cap under the rear seat squab.
AFAIR the earth feed point is on the X-member under front seats - somewhere near the center panel under the carpets. Could be a corrosion problem here too.

AndersDK · Unread post by **AndersDK** » 10 Oct 2004, 03:09

The BX does not have a voltage stabilizer in the instrument panel [:)]

jeremy · Unread post by **jeremy** » 10 Oct 2004, 04:57

much the same experience - took black plastic cover out of the floor and found the wire had shrunk, pulling plug off sender unit. Now reads full for 150 miles which is really useful!
jeremy

uhn113x · Unread post by **uhn113x** » 10 Oct 2004, 15:38

Voltage stabilisers (not present on BX) are nothing to do with damping the fuel gauge, but are to supply a regulated voltage (usually 10) to the instruments, which otherwise would receive a supply of anything from 12 to 14.8 volts, affecting the readings (which it does on a BX!)
The fuel gauge is usually damped by working on the hot wire or bimetallic strip principle, or is magnetically damped.

tomsheppard · Unread post by **tomsheppard** » 10 Oct 2004, 17:15

You can put in a 10 volt regulator chip for this but it isn't worth it. They do swing around and act as inclinometers so the best way to interpret them is as an indicator, not an instrument.
It works like this:
fill tank.
At 130 miles needle moves off full stop (You have used the fuel in the extra tank)
At 330 miles, the needle is vertical and showing 1/3 used. No, it's 60%.
at 550 miles, The evil eye begins to flash
at 630 miles, FILL UP!

G4EIY · Unread post by **G4EIY** » 11 Oct 2004, 02:33

Hi,
I can concur that the swinging neadle is usually a bad connection to the sender located under the back seat.
Also the sender is AFAIR, a float that wipes on a glass fibre printed circuit board, and the bottom part of the printed circuit is prone to be damaged, just disapears, this causing the gauge to drop to zero at low tank fuel levels.

uhn113x · Unread post by **uhn113x** » 11 Oct 2004, 12:43

Taking this a bit further - on an A-Series:
Reads 1/2 on left turn - nearly empty
Reads empty on right turn - just under 1/2 full (or 1/2 empty if you are a pessimist)
For a DS, transpose 'left' and 'right'
One day I will see what sticking a 500mfd electrolytic across the gauge will do.
<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by tomsheppard

You can put in a 10 volt regulator chip for this but it isn't worth it. They do swing around and act as inclinometers so the best way to interpret them is as an indicator, not an instrument.
It works like this:
fill tank.
At 130 miles needle moves off full stop (You have used the fuel in the extra tank)
At 330 miles, the needle is vertical and showing 1/3 used. No, it's 60%.
at 550 miles, The evil eye begins to flash
at 630 miles, FILL UP!
<hr height="1" noshade id="quote"></blockquote id="quote">

tomsheppard · Unread post by **tomsheppard** » 11 Oct 2004, 13:52

it will increase the capacitance- not make the tank any bigger!

Unread post by **Jon** » 11 Oct 2004, 14:11

Thanks folks, will attend to the sender/connections this weekend, Vanny is sending down a replacement unit in case thats the problem.
Todays unusual fault appears to be with the supplementary fuel tank. Upon filling up this morning, lots of precious diesel started pouring out onto the ground. There's some problem with the supplementary tank , its soaking wet. I also spied that the bracket that should secure the thing is gone, replaced by some rope. Oddly neither the MOT tester or I spotted that before!

G4EIY · Unread post by **G4EIY** » 11 Oct 2004, 19:35

Jon,
I had the same problem with my td, relatively easy to make up a replacement.
I cut a strip from a sheet of bendable galvanized sheet, and used the old one as a template.
If the old one is completely missing, make a template from thin cardboard.

uhn113x · Unread post by **uhn113x** » 11 Oct 2004, 21:25

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by tomsheppard

it will increase the capacitance- not make the tank any bigger!
<hr height="1" noshade id="quote"></blockquote id="quote">
Thought it may stop the (moving-iron) movement bouncing as much - may need to be biggerm as total R in circuit is low. I saw a fuel gauge off one of those 50cc 'hairdryer' mopeds once, that had no return spring, and the moving iron sat in a pot of silicon goop, so it retained its reading when the supply was switched off.