According to Bentley and TIS, from front to aft direction, the relays are:
fuel relay
DME
Oxygen sensor heating (emissions fan???)
http://tis.spaghetticoder.org/s/view.pl?1/00/30/72 Today I plan on doing the following:
Remove stock 318ti fuel pressure regulator and valve (located under driver's side) and replace with the same set up from my M3 donor. I believe the 318ti is 3.0 BAR and M3 is 3.5 BAR. Also, the fuel filter on the M3 had about 5 miles on before the car got totaled so I will swap the entire assembly.
I'm also going to check my fuel hoses. I'm 100% certain they are not mixed but you never know...
I also just found my Peake code reader so I'm going to plug it in and see what I get.
I sure hope it's not the fuel pump. Everything I've disassembled from the TI (nose, etc.) in inside the car.
T/S continues...