FYI,
In the xdp file of most aircraft the universal lines of code to use are:
<Effect Type="Track" EffectName="fx_high_contrail" Location="emitter_eng0_exh_r" />
<Effect Type="Track" EffectName="fx_high_contrail" Location="emitter_eng0_exh_l" />
You can tell that this will work if you see
<Effect Type="StartEngine0" EffectName="fx_engstrt" Location="emitter_eng0_exh_r" />
<Effect Type="StartEngine0" EffectName="fx_engstrt" Location="emitter_eng0_exh_l" />
already in the effects section.
Only aircraft like ETO_P_51d_100_45 that didn't choose to incorporate the engine emitter locations in the model file need the x, y, z coordinates.