Fuel Sender Problem

[knlmotorsport]

I am having issues conneting the fuel level sender of my 1999 wrx to a SDL3. I have conneted it to a AT input on the SDL3 and it works until the fuel pump switches on. When the pump switches on the level drops from the correct level to -9.
Has anyone had issues with this before?
Any help would be greatly appreciated as i have been trying to sort this out for some time now.

Cheers

[David Ferguson]

The AT inputs have a pull-up resistor. I suspect your fuel level sender is connected to some other voltage source -- you might try connecting it to an AV input, then re-calibrating with the fuel pump on.

[knlmotorsport]

Thank you. I will give that a go.

[knlmotorsport]

Still having this issue. Turning headlights on and off also affects the fuel reading and fuel pressure sensors. Is this something simple i am over looking?

I am having issues conneting the fuel level sender of my 1999 wrx to a SDL3. I have conneted it to a AT input on the SDL3 and it works until the fuel pump switches on. When the pump switches on the level drops from the correct level to -9.
Has anyone had issues with this before?
Any help would be greatly appreciated as i have been trying to sort this out for some time now.

Cheers

[Scott@FP]

Sounds like a ground issue from the sending unit to the chassis and back to the battery.

[knlmotorsport]

Thanks I'll check that tomorrow. I've just wired it straight to the standard level sender.

[Holmz]

Thanks I'll check that tomorrow. I've just wired it straight to the standard level sender.

One wire or two?
Scott was talking abut the second wire, or black wire.

[knlmotorsport]

2 wires. I'll have to check all earths and "0" volt i think as it changes when lights are turn on and off and when the fuel pump switches on and off.
It also effects the fuel pressure reading.

[Scott@FP]

I'm not intimately familiar with WRX wiring but that sure sounds like a ground issue from somewhere between the fuel pump module to the main chassis ground for the fuel pump module. Voltage drops are effecting everything inside the module, fuel pump speed, fuel level etc. If you've put in a pump that draws a lot more amps than the factory one, in many cases (regardless of vehicle) the OEM connector pins are inadequate for the current draw and overheat and go into meltdown, inspect all connections carefully.

[Holmz]

Good points Scott.
If one ran a test point from the battery and measured all ground voltage at the ECU, Fuel pump and sender (with all combinations of pump and ECU both powered and off (with the engine running and not running), that should give a pretty complete picture to be able understand what is happening on the ground side.
Running those extra wires to a volt meter should be pretty straight forward???