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Discussion Starter #1 (Edited)
During the course of removing and reconditioning the starter motor on my son's 3 litre 75/Milano last week my Alfa mechanic discovered that the previous owner had connected the computer return wire of the O2 sensor to ground, rendering it inoperative. Now the thing is that I have had this car since 2005 and it has worked fine like that. Anyway, Luigi connected the sensor up as it should be and the car started and idled smoothly. He was unable to test drive it due to lack of fuel and when my son drove it home it started running rough and backfiring and died in the middle of an intersection after about ten minutes. Luigi rang him and got him to disconnect the sensor at the intake hose end and the car started and got him another few minutes down the road before it died again. We got the emergency road service to come down and the car kept dying after running OK for five minutes or so. The patrolman tested the leads and there was no voltage coming from the sensor. A possible factor here is that the previous owner had installed a Megasquirt system which he never got fully tuned before removing it and selling the car.
My questions are:
1. Could the previous owner have done something with the O2 sensor or computer wiring in the course of installing the Megasquirt that allowed the engine to run with the return lead earthed which has led to it running badly with the O2 sensor connected correctly or disconnected altogether?

2. Is there another reason why someone would earth the return lead?

3. What are the usual symptoms of O2 sensor problems?

4. What else may have happened here that we can check for?

Any help will be greatly appreciated.
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