inspecting spark plug wires

[Evo_Spec]

hey guys, i just recently replaced my spark plug wires, but there really was no problem with my old ones, i just changed them because i never did since i bought the car. (the old one's were NGK so i didn't want to change them =P)
the new wires feel the same or maybe a little smoother but that could be all in my head too (engine feel)
but this brought up a question in my head: how do i know if i actually need to change my wires? is there a way to check them? is there a certain life to them?

[93vtecklr]

That is a good question.

[Evo_Spec]

i thought so too, my NGK's look fine, i've seen some pictures of people's spark plug wires on the forums where they have a crack in the spark plug holding part, but mine don't have that, just wondering if changing them was even necessary

[RS_OBD'oh_2]

Just a guess, aside from all physical defects.. I would try out the old multimeter and check the resistance end to end. I would think that you'd need a fairly accurate meter, otherwise it may just read as a dead short.

[mitmaks]

how much resistance should you be getting though?

[RS_OBD'oh_2]

depends on brand and length

[Inodoro Pereyra]

There are ways to check them, but but to do it accurately you need a bunch of fairly expensive equipment, so it's not really worth it (at least in my opinion).
A visual inspection will normally give you a fairly good idea as to the shape the cables are in. Other than that, as RS_OBD'oh_2 said, you can check the cable's DC resistance. Using a multimeter will be of little use, given the very low resistance you'd be measuring. From then on, you have several options: either you get a mili-ohmeter (the "cheap" choice, which will run you in the order of several hundred dollars), or you can build a Wheatstone bridge with calibrated resistors, get a precision galvanometer and a very stable power supply (about a couple of grand) to get a way more accurate measurement.
Anyways, that's only gonna give you a picture of the wire's DC behavior, what is normally known as a "static test". Better than a visual inspection, but will only take you so far, and a lot of "Buck for the bang"...
To really have an idea of how the cable performs, you'd need to make a "dynamic test", that is a test in where the actual working conditions of the cable are simulated to an extent.
For that, you'd need a square wave generator capable of generating a very high quality waveform of a fairly high voltage, and an oscilloscope (and of course the knowledge to read it), so you're talking about 2-3 grand again. Definitely not worth it (IMO) to test a set of wires that'd cost a couple hundred dollars at most.

[SuperK]

As I understand spark plug wires, the largest points you have to consider are:

1. Resistance
2. RF shielding.


You can have a wire with amazing low resistance, maybe a solid-core wire... however, it can cause excessive RF interference which inhibits other components, such as injectors, sensors and of course, your radio.

The closer to zero ohms, the closer to perfect your resistance in your wires are. Take a voltmeter, throw it on ohms and check your resistance. If it reads low, then you're golden...

... but both resistance and RF interference increases over time. I don't know how you could truly test your wires but at eight dollars, you got some beck arnely wires? It's just good full tune-up practice.

[Evo_Spec]

As I understand spark plug wires, the largest points you have to consider are:

1. Resistance
2. RF shielding.


You can have a wire with amazing low resistance, maybe a solid-core wire... however, it can cause excessive RF interference which inhibits other components, such as injectors, sensors and of course, your radio.

The closer to zero ohms, the closer to perfect your resistance in your wires are. Take a voltmeter, throw it on ohms and check your resistance. If it reads low, then you're golden...

... but both resistance and RF interference increases over time. I don't know how you could truly test your wires but at eight dollars, you got some beck arnely wires? It's just good full tune-up practice.

yeah, i got them off rock auto with the sale thing they got going on

[SuperK]

I got them for my friend, too. They looked all too familiar

[ninjajim4]

RS_OBD'oh_2 is spot on. look up in the shop manual for the resistance readings in ohms/ft. any digital multimeter will do. you'll be able to see if they're in spec or not and compare to your new ones

[Mad Cow]

You could also test the rubber shielding by spraying a mist of water over them at night and seeing if they make any sparks.

[kaube69]

Borderline off topic but where would I buy coloured spark plug wires ( red) I can't seem to find and on local car parts store website. Thanks in advance

[RS_OBD'oh_2]

wow, you should not have any issues finding these. I did a 1 second search for "Probe GT plug wires" and found them right away. NGK makes a red set. Anywhere that sells NGK will be able to order your wires.

[kaube69]

sorry i work midnights so im hella tired when i get home so i just typed in the obvious and it didnt come up..but thank you