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I just purchased a 1995 993 C4 (built 3/95). How can I tell if I have an engine wiring harness that seems to fail.

E. J. - 993 Alumni

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E. J.

Peter Topping

There are a number of issues that can point to a faulty engine wiring loom on a 993.
These are as follows:-

1. Battery discharges for no apparent reason.
2. Starter still runs after engine has fired up
3. Starter engages/starts when engine is running while driving
4. Spark voltage down on scope test
5. Engine runs lumpy
6. Engine will not run on 6 cylinders
7. Engine back fires and pops
8. Engine down on performance
9. Difficulty in starting engine
10. Black smoke from engine when starting
11. Smell of petrol when starting

The most serious problem is that the wiring loom can go “live” to the alternator; this is potentially a fire hazard that could happen at any time.

The wiring loom connects from the engine bay junction box to the injectors, starter motor and alternator – the alternator is live all the time carrying high current with no fuse protection.

The loom is shielded in a wrap. Cutaway the protective wrap this will reveal the sheathed cables within, this sheathing will probably be cracked in a “hooped” effect around the core of the cables. This sheathing is of the wrong material, becoming brittle and cracking when hot, this then shrinks revealing the core cables to short out.

This issue seems to affect the earlier non VarioRam 993's, strangely the replacement wiring loom has a different part number.

Porsche have to recognise this as a grave problem and have to take ownership of the situation.