Porsche Repair: porsche 911 sc repair, vacuum leaks, porsche 911

Question
I have a 911sc from 1979.The car occassionally backfires and the engine loses power at the same time.It may happen unpredictably.Otherwise the car is running well.The mechanic felt that the problem was with the ignition system or electrical wiring.The wires were changed doubly insulated.relays were changed and there is a new starter as well.when the problem happens I turn off the engine then restart and it solves the problem until the next time.It may happen several days later       or sooner.The mechanic plans to build a shield to protect the wiring from the heat of the engine.Any suggestions

Answer
j.,

Here are the typical reasons a Porsche with fuel injection will backfire:

1.  Faulty scondary ignition system ( cracked spark plug insulator, faulty plug wire, distributor cap and/rotor).
2.  Fuel injection: out of adjutment or "adjustables" worn excessively.
3.  Vacuum leaks at fuel injectors, intake manifold or hoses in general.
4.  A computer fault (sorry, this is on the "list" without any other specification, but the culprit is probably above anyway.

Based on your symptoms, I'd bet on #1, which is the hardest to "make" happen in the shop.

Good Luck.

Dave