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DIY - Fuel sender conversion for Factory X-fal cluster

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Fuel gauge interface for using resistive sender with factory X-fal instrument cluster.

Finally finished development of this and here is version 1. Uses an Emitter Follower amp type on the input which gives the gain we want and keeps current requirements low. and a basic common collector amp on the output. With some over voltage protection for the instrument cluster.


Development specifics:
This is what i used when building the circuit. It is an assumption that this circuit will work for all X-falcons that use a capacitive system.
Fairmont Ghia digital instrument cluster (Star wars cluster) - Requires output for Empty-Full 0.5-4.3v
240-33ohm fuel level sender: https://www.ebay.com.au/itm/VDO-Float-Arm-Gasoline-Diesel-Fuel-Level-Sender-Sensor-240-33-OHM/321479254400?hash=item4ad9a82180:g:XO8AAOxyVLNSvvHE

***** EDIT: It is recommended R4 is replaced with a 100r potentiometer to allow easier adjustment of low level/reserve capacity. ******



Preliminary steps:
Install the fuel level sender to allow full, or as close to full sweep as allowable. Set the "Low" level so that the sensors resistance is about 30-50ohms when the float is sitting on the bottom of the tank.

Regardless of sensor Ohm rating the following procedure will set the gain of the circuit and should give accurate full sweep of the display.
1. Fill your fuel tank to FULL. (Or simulate by manipulating the rheostat to the full position.)
2. Connect the circuit and power it up.
3. If D3 LED is illuminated, Adjust R6 pot until the led extinguishes. Stop adjusting the moment it extinguishes, You have now set an output voltage of 4.3-4.5v and your gauge should read full.
(If D3 LED is NOT illuminated, Adjust R6 until it illuminates, then proceed with step 3.)
(If you did not install the failure and over volt circuitry, At step 3 connect a volt meter between the output and ground, Adjust R6 till you get 4.3v)

Low level cal:
If there is a low level problem or for greater accuracy the low level can also be adjusted:
1. Install a 100 ohm Pot in lieu of R4.
2. Have the fuel tank empty (or simulate by moving the rheostat into the empty position)
3. Connect the circuit and power it up.
4. Connect a multimeter between ground and the output. Adjust R4 until the output reads 0.5v (The instrument cluster will show 1 flashing red bar/Empty)
(if the fuel level sender's initial resistance is too high, You will not be able to calibrate the low level. Maximum low level resistance is about 100ohm.

Note: The following must be carried out within 30 seconds of switching on the ignition, While the gauge is in fast acquisition mode. After this, the fuel level gauge reverts to normal mode and will respond VERY SLOWLY to changes in sensed fuel level.
1. Turn on Ignition.
2. Check the LED is not illuminated.
3. Press S1. LED should illuminate brightly and the instrument cluster fuel gauge will read full.
4. Release S1, Fuel gauge should return to fuel level as sensed by sender.

If the LED is illuminated:
1. Confirm correct calibration was carried out.
2. Check the Fuel level sender is connected. If it is connected, Disconnect it, and measure the resistance of the wire going to the sender, To a ground on the vehicle. It should be within the range of the sender. If it is not, Check sender and all connections. Proceed to step 4 if sensor is serviceable.
3. Connect the sense wire to ground (Wire that fuel level sensor connects to on interface unit), LED should extinguish. If it does not, the interface unit has a fault.

If pressing S1 does not illuminate the LED:
Check all connections. If no anomalies are found. Unit is faulty.

Circuit should be able to be tuned to use any restive type sensor. Senders of specific values not commonly found may need modification of some of the component values on the input side.

The circuit is NOT INVERTING. So senders like the 240-33Ohm sender designed to operate as Low R = Full tank. High R  = Empty tank. Will not work with this circuit, unless input is inverted. The easiest way to do this is to turn the rheostat 180º so it's essentially upside down. If this is not possible, Will im not going to cover inverting the signal here. The reason some senders are inverted, is so if it is disconnected or fails, the fuel tank reads empty. In my circuit, the fuel gauge will read full if the sender fails. However, the circuit includes basic failure mode detection. (The LED)

The circuit includes failure detection. For simplicity, the following components are for failure detection and over voltage protection, and can be omitted.
S1, D2, D3, D4, R7, R8 and Q3
If a sender not connected, or open circuit:
Q1 will be off driving the base of Q2 High and into saturation which may potentially exceed the max input voltage of the falcon instrument cluster. R5 is current limiting and may be sufficient to protect the cluster, but this is not guaranteed. Voltage may approach 8V into the gauge.
Because the risk of this failure mode been high (User error or sender failure), zener diode D2 is utilized to clamp the Q2 base voltage below 5.7V, in turn preventing the output from exceeding 5.5v
In order to establish an easy indicator of this fail mode, a lower brakeover voltage is chosen for D2 and D4 and R8 recover that voltage, using it to set a bias for Q3, which in turn illuminates the LED.

C1 and C2 stbilise U1, and cannot be omitted. 
D1 Prevents reverse polarity connection, protecting the circuit. It may be omitted, But if the user connects in reverse polarity the circuit will destruct.
R3 is base current limiting for Q2
R4 sets the Minimum output voltage. this can be changed to set depending on the sensor and installation. Alternatively it can be replaced with a 100-200ohm pot and calibrated as above.
R5 is current protection for Q2
C3 is for damping noise from the sender, May be omitted?



Digital instrument cluster fuel level gauge I/O Data:


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Getting this circuit on a custom PCB and will have enough to make and sell 7 units, fully assembled ready to wire in or self assembly.

Price to be decided still.

As with all the stuff I make for the forums, not in it to get rich so can expect them to represent the cost of manufacturing. Estimate between $40-60 each inc Assembly and post. 


Expressions of interest/reservations are welcome. 


Still need to receive and test the pcb's and proove circuit function, estimate ready to sell/ship in 2-3 weeks. 

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Just an update, 
I've made the fist unit. I've still got a bit of work to do before i can ship them. Bit of testing and parts list/cost figuring out to do. I wanna make sure i got all my ducks lined up and quacking the star wars theme before I ship em out.
The idea is that whoever buys em, gets it, Wires it into their stock fuel sender loom. Adds 1 wire for the fuel sender. Then use a screwdeiver to adjust the low level/high level readings for whatever sensor they used. And it's done. QuUUUAAAAACCCCCKKKKKKKKKKK..... quack-quack-quack-quack-quack-quack-quack-quack-quack-quack-quack-quack-quack-quack-quack-quack-quack-quaaaaaaccck... quack-quack-quack-quaaaaack QuackkkKKKKK. quack-quack-quack-quaaaaaaaCCCKK QUACK. quack-quack-quack-quaaaaaaaCCCKK QUACK.  QUACK-QUACK-QUACK QUAACK! *Credits roll* 



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so.. would this work for an E series fuel tank in an X series also (as in, if someone was fitting an XG tank into XD ute for EFI(rust reasons/availability even)  or efi wagon(EA to EL into Xseries wagon for EFI LS1 or barra etc or rust/availability etc. 


i googled and found the range is EA to EL is 2-220 

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Yep. Should work for any sender, as long at it is not inverted. In other words, low ohm= empty and High ohm=full.

So a empty 2-300 full, will work. But not a empty 300-2 full.

The one I link to in the OP, uses 2 screws to mount it to whatever you want, so you simply install it upside down, and it goes from a full-empty 240-33 to a empty-full 33-240.

Does that make sense?


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Hey crazy2287

On 8/30/2018 at 11:10 AM, Crazy2287 said:

$58 inc express post with tracking. (Can combine post)
$45ea if your close by and want to pick it up.

More info will come, I expect to be able to ship on Tuesday 11th September.

7 units available. First in best dressed.

Hey bud do you have any left??

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15 hours ago, Crazy2287 said:

Yep, got 2 left. Ones pulled apart on my bench pending a mod for non-digital clusters which i hope to finish in the next day or 2, the other is ready to ship.

Cool can you call me

i sent an inbox to you with my ph number.

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