BX Fuel Gauge & Warning light Problem

Roscoe · Post by **Roscoe** » 26 Oct 2005, 14:19

Hi all
I replaced all the bulbs in my instrument panel after swapping in a proper temp gauge for the warning lights on the TZD a few weeks ago. Everything worked fine except the fuel gauge - it was intermittently jumping around and sometimes dropped right to the bottom and stayed there - but it had been doing that for over a year, so didn't worry me too much as I go by mileage to fill up. However last week, it totally quit working and doesn't even flicker off the bottom, and now the red fuel lamp is also flickering on and off intermittently (never saw it light up before, so probably had a blown bulb). What I want to do is prove it to either the sender in the tank, wiring between tank and gauge or gauge itself before ripping things apart. Is there an easy way to do this (via tank access under rear seat, etc) and if so, can I just apply an earth to one of the wires via a test lamp and see if the gauge moves? Any other ideas?

citronut · Post by **citronut** » 26 Oct 2005, 21:23

it is probably the sendor,but you should be able to work out which wire to earth out,cant remember how many wires there are on the sendor,if there is three one will be a permanent earth,the oters will be a return earth to the gauge and a return to the low fuel warning lamp
regards malcolm

AndersDK · Post by **AndersDK** » 26 Oct 2005, 22:19

The tank gauge reads full when the sender cable is earthed. And the low fuel warning comes on when it's cable is earthed. This is of course only true if the cable is in good shape over its entire run from sender to fuse/junction box.

Possible known problems :
1) bad earth (out) in the cable
2) bad connections in cable & sender connectors
3) cable chafed (earthed) somewhere over its run
4) cable disrupted over its run

rarely the sender unit is faulty.

Using a standard testlamp with needle tip and croco clip - connect the crococlip to nearest interior light +12V as it is protective fused and always supplied (remove glass). Then search for the earth in the 3 lead sender cable connector. The testlamp should light up clearly.
Now insert a paper clip into this earth - and connect croc clip here.
Searching with tip on the other 2 connections should bring on either gauge on full - or the warning light.

Roscoe · Post by **Roscoe** » 26 Oct 2005, 22:53

Thanks Malcolm and Anders - I'll check it out first thing this weekend. The way the gauge has been acting, I suspect dodgy earthing, but wanted to prove it. It used to work properly when the tank was between 1/2 to full, but lower than that the gauge started bouncing around, now it doesn't do anything at all. So at least I can prove it into the sender or wiring. I take it from the description of the way the earth is provided that the sendor acts as a potentiometer - so if it is that I should be able to use a meter to check it out.

citronut · Post by **citronut** » 26 Oct 2005, 22:58

yes its a float inside a plastic tube which runs up and down a metal strip
regards malcolm

Roscoe · Post by **Roscoe** » 30 Oct 2005, 08:59

I checked out the wiring from the tank sender to the gauge - using a test lamp from the interior light 12V supply as Anders suggested - both gauge and warning light worked, so that pointed to the sender. I pulled it out and got it apart - was a bit of a mess! Bits of the resistor wiring had come off the PCB and wrapped around the float, so I got all that cleaned up and tested it for resistance in various places - showed a varying resistance as I slid it up and down. The conductive strip from the light return down one side had come off the PCB so I just cut it where it was still fastened and left it - don't see how to replace that and didn't want to chance soldering on a board that was fairly saturated with diesel. After reinstalling it, the gauge showed full (I had about a half tank, and after driving it around awhile, didn't move at all. So I pulled the one out of my 16V parts car and swapped it in - it showed about 1/4 tank and today when I filled the TZD up, it went up to full...so I'll see how that one goes. Might do some checking around and see if anyone here repairs these things...they are pretty basic but after being saturated in fuel for years, can present a few unique problems...like getting anything to stick to them!

citronut · Post by **citronut** » 30 Oct 2005, 11:22

its easyer to just replace the hole unit rather than trying to repaire the old one,then you just doing the job once insted of several times
regards malcolm

Roscoe · Post by **Roscoe** » 31 Oct 2005, 00:07

Can you still get the sender units and are they a 'reasonable' price? Haven't tried over here, but if other parts are any indication, they probably cost as much as the car is worth

classic2cv · Post by **classic2cv** » 31 Oct 2005, 08:29

i have the same problem with my fuel gauge

I have a old ZX td that I’m about to get rid of

do they use the same the sender unit?

i would be handy if i could swap them

citronut · Post by **citronut** » 31 Oct 2005, 08:51

im not sure of the cost,also i would think if the tank is a diferant shape the sender will calibrated diferantly,but its worth asking your dealer if they have the same part number
regards malcolm