full = empty fuel gauge issue.

Post Thu Sep 13, 2012 11:59 pm

Just got my new turd and its had a replacement fuel pump recently, but i'm not sure what they've done with the wiring.

Full and empty are backwards, when the tank is empty the light is on but the needle reads full. When you put fuel in it the needle goes down.

I haven't looked at it yet, can anyone shed a light before I do?

Post Fri Sep 14, 2012 12:22 am

They have swapped the 0v and 5v i guess at the tank?

Post Fri Sep 14, 2012 1:21 am

Possibly..!

Post Fri Sep 14, 2012 8:46 am

Minimayhem81 wrote:They have swapped the 0v and 5v i guess at the tank?

Nope! That wouldn't explain it as you describe.
Supply is 12V, not 5V, but even if somehow they had managed to get 12V on a wire that should be earthed, this wouldn't explain the fuel light. When the low level switch is off, it's off, and the lamp couldn't light however it was connected.
First thing to do is to lift the rear seat cushion, disconnect the plug and socket under the vent pipe tube, and try earthing, in turn, the brown/grey and brown/green wires in the half that doesn't disappear down though the seat pan, with the ignition on.
Earthing the first wire should make the light come on, and earthing the second should make the gauge go from zero to full.

Post Fri Sep 14, 2012 9:10 am

Brianmoooore wrote:
Minimayhem81 wrote:They have swapped the 0v and 5v i guess at the tank?
Nope! That wouldn't explain it as you describe.
Supply is 12V, not 5V, but even if somehow they had managed to get 12V on a wire that should be earthed, this wouldn't explain the fuel light. When the low level switch is off, it's off, and the lamp couldn't light however it was connected.

He says that the light is on when it is empty. But not if it goes out when fuel is added.

Ben

Post Fri Sep 14, 2012 9:49 am

I'll explain again, when the tank is empty the light is on and the needle reads full. I put fuel in and the light goes off and the needle goes down.

The light works but the needle reading is back to front. Full = empty .. and.. empty = full.

Post Fri Sep 14, 2012 1:46 pm

Check that the brown wire to the three pin plug on the fuel pump assembly is intact and actually goes to earth.

Post Mon Sep 17, 2012 2:03 pm

Right had a look today, the wiring plug to fuel sensor seems fine. I bridged the pins this is what i got;

1-2 - Nothing, needle stays on empty.
2-3 - Needle shoots to almost full, (the tank is almost empty btw)
1-3 - Needle stays on emtpy, fuel light comes on.

I tried looking to see where the brown wire in the harness goes, but I can't see where?

Post Wed Sep 19, 2012 8:01 am

Its also the larger tank with 2 senders.. still can't figure this out.! Could it be an issue with the instrument cluster?

Post Wed Sep 19, 2012 9:50 am

Ok tested resistances, both senders read 0.02 and ground points seem ok.

I took the right hand side sender out, (4 bolts) and tipped it up and down to see if the float works ok, interestingly when the float is at the top of the sender the gauge reads full as it would normally and when the float is at the bottom of the sender it reads half full on the fuel gauge with the fuel light on.

Is it possible I have the wrong sender in the tank?

Post Wed Sep 19, 2012 11:16 am

how does the other one come out? It doesn't have any apparent 8mm nuts like the other one. Just 2 pin connector.

Post Sun Oct 07, 2012 9:09 pm

Ok got it out, required some persuasion from my Birmingham spanner....

Ok, when I unplug the secondary fuel sender the gauge falls to zero, when I plug it in with the sender upright the gauge reads full, when I tip it upside down it reads full too.!

I'm guessing the sender is dead as it reads the same high and low?

Post Sun Oct 14, 2012 4:42 pm

Cheers Willnz,

Yeah the float is working fine, I'll hunt down another sender and get back to you with results.

Thanks for all your help.!