06 WRX cluster signal for fuel gauge

[Hobby Racer]

I'm using an 06 WRX dash cluster in my 818R race car and need to drive the fuel level gauge. I have an aftermarket ECU so I need to emulate what ever signal the factory ECU and or Body Integrated Unit sends to the combination meter to drive the fuel level gauge.

I've been through the FSM and it looks like the combination meter gets a digital signal from the Body Integrated Unit, not a raw ohm reading from the sending units.

Does anyone have knowledge of the signal the combination meter is expecting?

OR

Has anyone disconnected the fuel level gauge from the combination meter microprocessor and tried to drive it directly?

Thanks

[904svo]

The fuel gauge supply 12Volts to the 90 ohm fuel gauge sending unit. The BIU has nothing to do with the fuel gauge. This is what
I found out on my 2007 ECU in my kit car.

[Hobby Racer]

I think I confused myself reading the following two sections of the factory service manual.

combo.png schematic.png

The reason I need to fake the combination meter signal is that I only have the main fuel level sender. The secondary has been removed as it seemed unneeded in the single cavity FFR tank. So I only have 0 - 30 ohms from my single sending unit.

I have been able to get the meter to work by sending a PWM signal based on the readings from the single sending unit, but it is unreliable when the car is moving

I think I may just need to buy a new secondary fuel level sending unit... anyone have one laying around?

[STiPWRD]

The 06 wiring diagram I have shows that the fuel sender is two resistors in series tied to ground on one end and to the ECU (pin B10) on the other. This is equivalent to the way it's setup on my 02 harness, which works with my 06 sti cluster. So, I guess the ECU digitizes it or just sends an analogue voltage to the cluster? All I know is that I deleted my integrated unit and the fuel gauge works just fine. By the way, I have the Boyd tank and had to flip the sender so it would read correctly but I believe the cluster wants to see 0 Ohms when full and 90 Ohms when empty.

06 wiring.jpg02 wiring.jpg

[Hobby Racer]

Yup, its looking like I need to hit the junk yard and get a secondary fuel sender and install it.

[STiPWRD]

A bit pricey but worth a look and should give the right resistance:
http://www.fueltankparts.com/0-90-ohm-sending-unit.html

[Hobby Racer]

I thought of that but I'm not sure if the mounting flange matches the Subaru pattern on the tank. If not its more trouble than its worth, go with OEM.