Testing Spark Plug Wires
Thread Starter
Instructor
Joined: Dec 1999
Posts: 195
Likes: 1
From: Van Buren AR
Testing Spark Plug Wires
My pace car has been slowly loosing power lately and I have had to continually set the idle higher and higher. I pulled the plugs and three of them were fouled. One was really bad. I ran a compression check and all the cylinders are fine. I thought that I must have leaking valve stem seals so I replaced everything in the ignition system except for the ignition module and the spark plug wires thinking I would change the seals this winter when I have more time. When I fired the car up, it ran just as bad. I pulled the spark plugs the next morning and the worst cylinder had unburned fuel on the plug. I checked the resistance of the wires before I reinstalled them and they all showed low resistance as they should, I even compaired them to one new wire I have in the shop and they are all in the same range considering their lengths. Can spark plug wires show the correct resistances and still not fire a plug properly? The worst cylinder was number 7 and the other two that are not as bad are numbers 2 and 5.
Melting Slicks
Joined: Dec 2000
Posts: 3,407
Likes: 2
From: Carmichael CA
Re: Testing Spark Plug Wires (Arkansas Flash)
What was the resistance readings? They should be reading around 7K ohms. Wires can read as high as 10K before they need to be replaced. If they read less than 7K then I would suspect something is wrong with them, for example oil soaked or other contamination. The longer wires will read higher than the shorter ones, but for standard resistance wire none should be under 7K or over 10K.
Thread Starter
Instructor
Joined: Dec 1999
Posts: 195
Likes: 1
From: Van Buren AR
Re: Testing Spark Plug Wires (Rockn-Roll)
I thought that OEM wires were about 6,000 to 20,000 ohms per foot and that aftermarket wires were in the area of 200 ohms per foot. Mine all run in the latter area and are proportional to their lenghts.
Race Director
Joined: Sep 1999
Posts: 11,361
Likes: 383
From: Plano TX
Re: Testing Spark Plug Wires (Arkansas Flash)
Yes, wires can ohm out good and still be bad. My biggest problem with plug wires has been arcing. I have headers and the accell wires I used to run would only last a few weeks (!) before they would arc thru the boot to the head (ground). Ohmed out fine but didn't fire the plug. Sometimes you can spot the arcing when idling the car at night and looking carefully.
Finally gave up on accell after several sets of their (junk) wires and got Borg Warner spiral core. No problems since.
Finally gave up on accell after several sets of their (junk) wires and got Borg Warner spiral core. No problems since.
Race Director
Joined: Sep 1999
Posts: 11,361
Likes: 383
From: Plano TX
Re: Testing Spark Plug Wires (zwede)
Btw, there's a neat little tool that will measure the peak voltage in the wire. I got one and it makes it easy to spot bad wires. Broken wire will read high before the break, and low/nothing after. Arcing wire will read low. Made by Actron and was about $50.
