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VOLVO 740/760 TURBO MODELS 1986-90 diagnostic checklist

VEHICLE OCCASIONALLY BREAKS DOWN ON ROAD OR FAILS TO START (but sometimes starts after waiting). Problem is intermittent but GETTING WORSE. Breakdown services (repeatedly) diagnose engine management ECU (Bosch Motronic) failure.

    1) Problem is more likely to be LUXOR injection amplifier ECU which is part of traction control system - standard fit to these cars whether traction control specified or not. Luxor ECU is black painted cast alloy box mounted vertically immediately behind battery with connector on top. Luxor ECU takes 5V level output signal from Motronic and amplifies this to drive injectors. WITH TRACTION CONTROL FITTED - If the ABS system detects drive wheel speed differential (brakes NOT applied), this ECU will switch off first 1 injector, then 3 injectors (if wheel speeds still different)

    2) Liberally spray Luxor connector and pins with WD40 and road test before proceeding.

    3) Diagnosis takes some time and involves using oscilloscope to monitor input (Luxor pin 16) pulse signal from Motronic and output pulse to each injector (Luxor pins 17/18/19/20). Failure is indicated by reduced AMPLITUDE of output injector pulse (which can be momentary and intermittent) - banging Luxor can help speed things up!

    4) Sending Luxor ECU for reconditioning anyway may be best option!

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