As you have found out there are some variations in the use of the 4 relays within the MFRU. If you find an ECU pinout diagram & follow the wiring into the MRFU (& out again) you can check what the various relays do (use a multimeter to confirm continuiity). My car is a 1994, originally with the old 1.4 K series. 4 relays were used controlling lambda sensor heater, fuel pump, starter & injectors (IACV & charcoal cannister). The lambda sensor, IACV & charcoal cannister were removed a while back, & I installed a separate relay for the starter for obvious reasons. However when I was getting a misfire, & odd fuelling problems, I got rid of the MFRU in favour of standard relays to just control power to the fuel pump & injectors.