Originally Posted by GTTuner
I'm actually surprised the actual FP supply voltage comes from the ECU. I'm normally accustomed to seeing the ECU control a relay that is wired to B+.
I guess it's just a Subaru thing.
I'm not convinced at all that the ECU directly drives the fuel pump . That doesn't make much sense. There's too much current. I've NEVER seen a sequential fuel injection system which does that. I looked through the '05 LGT service manual and unfortunately the fuel pump control pins on the ECU are not specifically detailed in the pinout. We do have this basic diagram though:
In red I have shown where I believe the main power for the fuel pump comes from, which is listed as fuse #11. It's highly likely that the ECU controls a few transistors in the control module which in turn regulate the current to the pump.
If any of you have worked on older 90s cars, a lot of them have various types of seperate/external igniter boxes for the ignition system. SR20DET and 13BREW engines have these kind of boxes for their distributorless systems, plus GM and Honda have ignitors for their distributors with electronic spark advance. These modules contain various transistors and other circuits which then control the ignition coils. The ECU doesn't ever directly drive the ignition system, and I highly doubt Subaru is directly driving the fuel pump either.
The LGT ECU switches on the fuel pump relay which supplies the main current from the fuse box for the fuel pump. The control module is in-line with this current supply and a chassis ground. Two pins from the ECU may control transistors in the control module which in turn control the power and/or ground to the pump itself.