Plug wires

[Porsche 935]

I was looking through the maintenance records I got when I purchased my 1984 Carrera. Looks like no one has ever replaced the plug wired. Anyone know the difference between the Beru and the PVL wires? And if I ohm the old ones out just for grins, what should the ohm range be?

[Dave Colangelo]

The first thing to check with old wires is if the case has degraded and is allowing shorts. Go into the garage at night and start the car up, with all the light off take a look at the engine. If the casing on the wire is bad (and it most likely is) you will see small arcs from the lines to ground.

A visual inspection may also reveal bad/cracked/degraded casings. Our host has lots of great choices for replacement wires.

I dont know the ohm range off hand but I would check all 6 for consistancy if you are worried.

Regards
Dave

[Porsche 935]

I would think after 30 years and more than 200,000 miles, they are probably not in the best working condition.

[darrin]

I'm still running the original wires that came with my '86 targa (175k miles) -- they're not super pretty, but don't arch or provide any other signs of distress/problem. I'm staying in the "if it ain't broke" camp on this for the time being and focus on timely replacement of wear items (rotors, plugs, etc.)

[Arne2]

Maybe, maybe not. Like you, I have an '84, mine has only 170,000 miles. Also like you, there are no mention of plug wires in the extensive records I have for my car. But when tested in the dark of night, my car's engine compartment is totally dark. And the car runs great. So I've not bothered to replace mine so for. I look them over at least once a year, including the night test.

[RichardNew]

Spark plug wires are easy enough to check.

1. Set the multimeter to 20 kΩ
2. Attach one contact to each end of the cable
3. Read the resistance

Permissible resistance values are:

1. Ignition cable with a copper core: 1 to 6.5 kΩ
2. Inductive resistor and carbon resistor: The value is calculated based on the resistance per meter multiplied by the length of the cable, plus tolerance
3. Ignition cables with inductive resistor: Here the resistance can be between 2.2 kΩ and 8 kΩ
4. Ignition cables with carbon resistor: The resistance per 1 m cable is 10 kΩ to 23 kΩ

Spark plug wires don’t wear out as much as they suffer damage when being removed. The biggest cause of damage is caused by removing the wire from the spark plug.



Richard Newton
Electrical Tools

[Porsche 935]

I looked in the factory manuals and no specs were given. But it did say their were 2 types of rotors. A 1k ohm and a 5k ohm, and said always use the 1k ohm. In the past I have seen the extensions at the end of the plug wire go bad and arc across rather than fire. Reason I am looking into this, sometimes it misses when accelerating from start and wideband shows richer like unburned fuel. But problem is random. It does not due it at cruize, and pulls good at wot. Also idles great.

[85911]

FYI, I replaced my wires last year only because one was broken. But, all of the coverings were showing signs of wear. I have an '85 Carrerra with ~68,000 miles.

The readings at the time were:

old wires:
#1 open circuit: plastic connector- .9 M ohms, wire- 3.0 ohms
#2 3.08 kohms
#3 2.8 kohms
#4 2.92 kohms
#5 3.07 kohms
#6 3.08 kohms

New wires, Pelican, Beru: #'s 1-6 2.9-3.3 kohms
coil wire 0.0 kohms.

I don't have the information RichardNew has above as to whether or not they were inductive or carbon resistor type. The Pelican information did not state this.

[stlrj]

Ohming ignition cables is meaningless since it tells you nothing about the integrity of the insulation and it's ability to contain high ignition voltages. A more significant test would be with the application of some liquid, like windex, on the cables while at idle.

In the industry, high tension cables are tested with a Megger tester capable of 15kV or more. Not the sort of equipment we could afford or have lying around our garages which is why I recommend windex.


Cheers,

Joe
87 Carrera which passes the Windex test!