I think the burn transistor is (NDT456p) and driver FMMT4401 NPN (I think ). Try changing the main part first (Fdd6676) and remove the BURN TRN from the circuit. Make sure the (Gate) is getting voltage by simulating a start or a starter test from the GSU before replacing that TRN. If you can borrow the pump or the glow plug TRN (without damaging it)and use it for testing.
One of the jobs of the flux is to remove any oxidization from the parts being soldered. Those oxides are still present in the remaining flux and should be removed.
Just my .02 wiorth, no flames intended.
I dont know it you every try acetone but it work real good for board cleaning.