tdci fuel sender resistance range

[roverrescue]

Have puddled about online but drawn a blank.
It seems the newer 2.4/2.2 tdci defenders still operate the fuel sender/ gauge via a variable resistor style setup. As opposed to some funky CANBUS / ECU system.

But Im struggling to establish the resistance range.

Im putting a second tank under the tray with transfer pump and contemplating putting a sender in it with a switchover relay so when pumping it across to the main tank the dash fuel gauge reads the reserve tank.

So I just need to match the resistance range of the factory unit.

If no one knows I suppose I can pull the factory sender and test it but the easy option would be appreciated

S

[roverrescue]

Righteo,
So it took me a few weeks to use half a tank and make the measurements.
So this is for a 2010 2.4L tdci 130 defender.

Tank Full - 8 Ohm
Tank half - 50 Ohm
Tank empty fuel light just on 62L to fill - 194 Ohm

So possible VDO options
220.003 - 10 to 180 Ohm range
Or
A2C59510171 - 3 to 180 Ohm range

Neither perfect but close enough

Steve

[bee utey]

If you use the 3 - 180 ohm unit you can add a series resistor to the sender wire to fine tune the reading, the value depending on whether the full reading or the empty reading is most important to you.

[roverrescue]

Good thinking beeutey
On my factory gauge it was reading above F at 8 Ohm
And about 1/8 tank at 194 Ohm with fuel light on

Fuel light and warning chime must be a function of resistance as there are only two wires from sender to dash.

I'm guessing the fuel light comes on at say 193 Ohm

So putting a 15 Ohm resistor into the VDO line will ensure the light will come on for the added tank in the last litre or so of capacity ... It might read a touch under full

But to check I'll take a reading when needle on the F

Anyways ramble finished

Steve

[bee utey]

Actually I completely stuffed that up. Adding resistance will only make the problem worse. What you need is the 10 - 180 gauge and put a 2200 ohm resistor across the tank sender. The way to calculate two parallel resistances is:

R = 1/( (1/R1) + (1/R2) )

So using 194 ohms and 2200 ohms gives a combined empty resistance of 178 ohms, ideal for the gauge. In theory you could also add a 2 ohm resistor in series but that might be splitting hairs.

[roverrescue]

So I just had another measure 75km on from "full" tank and gauge is a smidge above full on the Gauge - resistance is 13 ohm

So my reckoning is I need a sender which runs from 15 Ohm full to 195 Ohm empty

So as resistance in series is added surely running the VDO 3-180 ohm sender with a 15 ohm resistor on one leg will give me a pretty accurate factory gauge ?

Let's put it this way I just ordered the A2C59510171 and seems I can find an 18 Ohm resistor ... Should be close enough

Steve

[bee utey]

So I just had another measure 75km on from "full" tank and gauge is a smidge above full on the Gauge - resistance is 13 ohm

So my reckoning is I need a sender which runs from 15 Ohm full to 195 Ohm empty

So as resistance in series is added surely running the VDO 3-180 ohm sender with a 15 ohm resistor on one leg will give me a pretty accurate factory gauge ?

Let's put it this way I just ordered the A2C59510171 and seems I can find an 18 Ohm resistor ... Should be close enough

Steve

You're right of course, I swapped the gauge and sender in my mind. Didn't reread your original post, you see.

[roverrescue]

Have another gin bee
Will make everything bettererererererer

S

[TimNZ]

Just remember the puma does the anti running out of fuel thing. From memory >6% it induces a misfire, >3% turns the engine off. So you'll need to be careful if you want to get the most out of your tank.

Cheers,

[roverrescue]

Tim
As far as I can ascertain fuel level, warning light and subsequent running with a miss is only sensed via the fuel sender
As above it seems the fuel light is triggered with 193 Ohm
I'm guessing the running with a miss will be triggered at about 200 Ohm

My plan is for the second tank sensor to go high enough resistance to trip the warning light and chime but never high enough to set off the run dry.
The setup I'm planning won't directly feed the engine merely the main tank so no issue of running the IP dry

After talking with the guage shop I ended up ordering the 220.003 VDO sender
It can be run as 10-180 ohm with full to empty or empty to full.
I'll mod the 180 up to 195ohm with a resistor ... Won't quite read full when full

Meh

Steve