Looks to be a P-Channel MOSFET, though I can't find any gate activity in testing, this board may have other issues.
1 = Battery VCC, Cap to GND
2 = Output, CAP to GND (VCC to fuel pump relay, i think)
3 = ?
4 = GND
5 = ?
Tab is isolated from GND, no external flyback.
I need to dig further, got cut short with rain.