Spark Plug Wire Test

You can get a rough idea with an ohm meter. The wires will be in proportion to the resistance. Say if a 1' wire is 1K ohms for easy numbers, then a 2' wire would be 2K ohms.

Wires can have internal breaks though that might not show up until it is bent 'just' the right way and have external leaks.

I test them with a spray mist bottle of water also. I open the hood at night and mist the wires when it is running. If I get a fireworks display, the wires are leaking through the insulation or boots.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Jerry wrote:

Yes. Figure I've seen is not more than 25K ohms per wire. When I tested mine, two read infinite resistance - now there's a clue.

You would need to check the specifications in a service manual for your car, but if you test the leads and find them to all have about the same resistance (I think it is usually in the order of 10,000 ohms or so, but dont hold me to it) then they are at least all about the same.

I don't particularly like to use the time to test them with a vom. I find cables nowadays are a little fragile and I handle them as little as possible.

If one is bad, I replace the set. A spark plug tester will often tell you if one of the circuits is bad...then you just have to decide if it is the wire, the plug, or perhaps the distributor cap or rotor.

Start it up at night and look for arcing.

If you have an integrated DIS system like the Quad 4, of course, you may have to proceed differently.

For the cost of a set it is usually easier and better to just change them out if your in doubt of their condition. Figure you can test them by misting them with water and then pulling them off and measuring them. Not worth the time.

| Figure I've seen is not more than 25K ohms per wire. This is only the tolerable maximum quoted by honda

for their carbon core cableswww.magnecor.com/magnecor1/truth.htm for their prescribed plug gap ofmaximum 1.1 mm.

Mine use stainless steel strands coiled on carbon cores, has just 2 ohm per ft.

Don't get too worked up about the difference between 25K ohms and 2k ohms in this application. The voltage drop over a resistor is proportional to the amount of current that flows through it, the more current the higher the voltage drop.

At the high voltages used in auto ignition systems, the current going through the plug wire during when the spark potential is building up (immediately before the spark) is minute, as before the spark happens, the resistance of the plug air gap is in the millions of ohms. Once the spark happens the resistance of the air gap is now effectively zero. You do not need a large current flow through the spark at the end of the plug because this isn't what fires the fuel air mixture, by the time the arc has formed and is passing current, the fuel air mix is already ignited. So while 25K ohms may seem a lot, in this application it is a good thing as it greatly reduces the radio frequency interference emitted by your engine.

The spiral wound wire claims to reduce RFI but since it is a low ohm wire, current flow during the spark is much stronger, so you have a much stronger EMF pulse generated that counteracts the inductive effect of the spiral wind. I don't know about any studies that have been done on RFI for spark plug wires that compare these 2 types, but I can tell you that from the engine side of things, there's no difference between low-ohm spiral wound plug wire, and high ohm resistance suppression wire. So don't pay a whole lot extra for it, it's a marketing gag. (like many in the auto parts biz)

Ted

| Don't get too worked up about the difference between 25K ohms and 2k ohms u have no experience of high efficiency cables

| the more current the higher the voltage drop nonsense

| fuel air mix is already ignited a small spark cannot burn all fuel before piston's BDC, fuel continues to burn after exhaust valves open, this is why exhaust noise is loud

| greatly reduces the radio frequency interference emitted by your engine. The carbon core in a spiral wound cable can absorb RFI, I've bought 7 sets since 1980, no interference to radio / tv.

| no | difference between low-ohm spiral wound plug wire, and high ohm resistance | suppression wire. just find a shop with a demo set up, u will see for yourself

| it's a marketing gag. Stingy / sales men can stick to their obsolete cables. My buddy's 9-97 CRV's Sumitomo cables ( 8.9k ohm / ft ) are no match to a set ( like mine ) I gave him : torque rose by 15% ( his estimate, as a QS ), exhaust noise dropped by

30% ( my estimate ).

| (like many in the auto parts biz)

80% nonsense, I like to find an aluminium radiator, oil cooler, turbo charger