84 300zx dies in 20 minutes of driving

My friends z31 dies after 15-20 min of driving, like turning off the key. Cools down a little and fires right up and drives for another 15min. He lives some distance from me so I will need a good idea where to look. I found the distributor harness corroded and replaced it last time I was there, at least now it starts. He has replaced the coil and the ecu. Something is triggering the ecu any guesses?

it sounds like a voltage regulator problem