TDi Fuel sender weirdness
- Thread starter tobee1k
- Start date
tobee1k
Member
Tom, thanks for all that detailed information. Do you think my original theory could be correct - i.e. that I haven't lined the arrow on the top of the sender up with the arrow on the car floor. Looking at the tank, it's a bit of an uneven shape, I originally thought that the little arm wasn't able to fully extend and was only able to show 3/4 tank.
Paul, I'm thinking now you might be right but hoping it's just an alignment thing!
Paul, I'm thinking now you might be right but hoping it's just an alignment thing!
timmus
A2OC Donor
I'm currently at my parents' house, but will be heading back to mine after lunch. On my computer, I've got a few diagrams that'll hopefully help me answer this with greater certainty.
Cheers,
Tom
timmus
A2OC Donor
I've done a bit of digging...
The later fuel sender has highest resistance when the fuel tank is empty. This is the better system because it means that, should the connection between the sender and the fuel gauge in the cluster fail, the gauge will immediately show empty. In other words, any increase in resistance will reduce the perceived amount of fuel in the tank.
The early sender works the other way around. When the sender's electrical resistance is at its highest, the fuel tank is full. This system is a bit daft because any electrical fault that results in greater resistance, however minor, will cause the gauge to show more fuel in the tank than is actually the case. I'm not surprised that Audi changed this. What surprises me is that, after however many decades of making cars, they hadn't realised the flaw in this system a long time before the A2 was ever conceived!
Anyway, if we assume that your car is using the later sender, the symptoms are easily explained by a dodgy/corroded connection. More resistance means less fuel. So, when your fuel tank is full, the gauge shows 3/4 full due to the added electrical resistance in the circuit.
It does not, however, explain why the fuel gauge stops falling when it gets to the halfway point, as you explain in your original post.
Cheers,
Tom
The later fuel sender has highest resistance when the fuel tank is empty. This is the better system because it means that, should the connection between the sender and the fuel gauge in the cluster fail, the gauge will immediately show empty. In other words, any increase in resistance will reduce the perceived amount of fuel in the tank.
The early sender works the other way around. When the sender's electrical resistance is at its highest, the fuel tank is full. This system is a bit daft because any electrical fault that results in greater resistance, however minor, will cause the gauge to show more fuel in the tank than is actually the case. I'm not surprised that Audi changed this. What surprises me is that, after however many decades of making cars, they hadn't realised the flaw in this system a long time before the A2 was ever conceived!
Anyway, if we assume that your car is using the later sender, the symptoms are easily explained by a dodgy/corroded connection. More resistance means less fuel. So, when your fuel tank is full, the gauge shows 3/4 full due to the added electrical resistance in the circuit.
It does not, however, explain why the fuel gauge stops falling when it gets to the halfway point, as you explain in your original post.
Cheers,
Tom
Last edited:
tobee1k
Member
Hi Tom, thank you for that useful information. You’re right, the old system sounds like a crazy setup.
Alas, I just got back in from taking it all apart again, discovered that the arrows were nowhere near in line. Proper alignment has solved the problem, just went and filled up and gauge now showing full. The arrow on the car was covered over with a nice layer of gunk (that’s my excuse for missing it the first time!)
Anyway, lesson learned and thank you all again for the helpful input.
Alas, I just got back in from taking it all apart again, discovered that the arrows were nowhere near in line. Proper alignment has solved the problem, just went and filled up and gauge now showing full. The arrow on the car was covered over with a nice layer of gunk (that’s my excuse for missing it the first time!)
Anyway, lesson learned and thank you all again for the helpful input.