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Dies without visible reason, then resurrects hours later. Hmmm

1984 Peugeot with Bosch K-jet fuel injection system. It starts instantly when cold, runs fine for about twenty or thirty minutes, then dies and cannot be restarted. Next morning, it will start fine, and same thing happens. Fuel pump hums very loudly, but all seems to work. Any theories?

Check the Tachymetric relay, up under the dash bolted to the base of the steering column. If you open it up, you may find the wire that connects to the moving contacts has split at the base where it’s soldered. What happens is that as the wire passes current to the fuel pump, it heats up, which causes the wire/solder to change shape ever so slightly. When it changes enough, it breaks contact, and the car dies, and can’t be restarted. By the next morning, it has cooled enough to retake the original configuration, make contact, and the great circle of life continues.

You can fix the problem by soldering in a replacement wire. Ten minutes with a soldering iron, two hours to remove and then replace the relay.