http://www.the-ecu-doctor.co.uk/

or if you are elsewhere Google for a similar shop........

I'll be surprise that you fried the ecu if you did not turn the ignition key
"on" while charging (overvoltage charge ???) the battery.
Check all the fuses particularely fuses that are hot at all time  21&27 (on
board computer) and fuse 10 ,the unloader relay K7 and K5 in the fuse box
compartment if the key has been turn to crank/run position while charging.
Check also  the main and fuel pump relay (located in the engine bay, RH side
of bulkhead behind cover. 3 relays are there, from left to right the first
one is for the fuel evaporation purge valve, the second is the main relay
and the third is the O2 sensor and fuel pumps relay) The main relay (12v
coil side) pin 85 is feeded by the onboard computer and code relay, when
activated it feed (via pin 87) the ecu pin 18 and pin 35 with
12 V. The ecu, in return, ground his pin 20 who activate the fuel pump /O2
sensor relay (via neg. side of the coil) given power (from the main relay)
to those unit. So if battery voltage does not reach the main relay pin 85
that means that the fuse 21 and/or 27 is/are blowned or that your obc is
fu... up. If battery power goes to ecu at pin 18 & 35 but you don't have a
ground signal at pin 20 while the ignition key is on crank/run position,
then you have a problem with your ecu. I will also chek the ignition coil.
Further more assuming that all those things are ok, I'll check the crank
position sensor and the engine position sensor before spending
$$$$$ for a ecu.
N.B. location of relays assume a LH drive M3, must be the opposite for RH
drive,
but I'm 99% shure they are on the bulkhead behind a cover.

Good Luck

Sylvain