I have a question concerning plug wires in general. I have well grounded (pun intended ) understanding of electrical theory, electronics, etc. I have been working on replacing the clutch on my 87 GT for some time (it has been one issue after another, you can read this thread if your interested 87 GT Clutch Issue ). But while things are still accessible, I am using this opportunity to replace things that would be otherwise difficult to replace. So this weekend I started on the spark plugs and the plug wires. I purchased some from Rock Auto, and I am beginning to think that they are not any good. I know some of you will tell me that you get what you pay for, but I honestly don't remember how much I paid for them. They are "Blue Streak" brand plug wires, and what I am finding disturbs me.



I wanted to make sure the wires were sound, so I took a multimeter and checked them. This is what I got:

Distributor Wire, 16" = 230 ohms
Plug Wire 25" = 330 ohms
Plug Wire 28" = 380 ohms
Plug Wire 28" = 1.18 Kohms
Plug Wire 29" = 400 ohms
Plug Wire 30" = 6.03 Kohms
Plug Wire 34" = 1.30 Kohms

To me, it seems that a few of them (28 and 30) seem to be a little out of the expected range tolerance for resistance, but since I don't measure plug wires every time I get a chance, maybe this is normal. As a comparison, I measured another set of wires I got a few years ago, that were sitting on the shelf:

Older Shelf set:

Distributor Wire 16" = 5.28 Kohms
Plug Wire 23" = 7.7 Kohms
Plug Wire 27" = 8.6 Kohms
Plug Wire 27" = 10.10 Kohms
Plug Wire 27" = 9.16 Kohms
Plug Wire 29" = 9.46 Kohms
Plug Wire 33" = 10.08 Kohms

Now these seems to be grouped a little better and within a 10 or 20% tolerance, like most resistor type electrical elements. I know that the plug is the highest resistance element in the ignition system (gap, not the core), and this is why you need a coil to up the voltage to a level that will jump the gap on the plug, so that resistance is very high (100's of mega-ohms) until the gap is bridged and then it drops to almost zero. The built in resistance of the plug electrode and the wires, then, is to keep the current low enough, that it doesn't burn up the coil.

I guess my question ... are the resistance values of the plug wires really that critical? The plug wire and the core resistance of the plug will add together, so they can really be considered one load.

The other thing that bothers me, is the "Blue Streak" wires are supposed to be the better ones, with 8.5mm cores, but their boots for the plugs don't even fit the factory heat shields:

Blue Streak Wire



Cheap auto parts plug wire



Opinions? Thoughts? Condemnations?

Can't you tabulate your results in Ohms/inch?

Maybe there's also a variable contact resistance at the crimp at each end; this variability would be more apparent for lower resistance wires.

I can measure my (used, but ran well) Accel 8 mm resistor-type wires next weekend, so we can get more data.

But I haven't heard of (doesn't mean it's not) resistance as being a useful troubleshooting method for wires. Usually, I spray water on the running engine, and then look for small blue sparks where there is arcing through the insulation.

The boots not fitting in the shields would be a deal-breaker for me. I tried wires without shields, and the boots crumbled.

with a name like Blue Streak, they can't be any good.....

Actually, it's a brand of Standard Motor Products....a low budget parts supplier.

[This message has been edited by Gall757 (edited 09-20-2017).]

From what I know, resistance in wires and plugs is to prevent emitted EMI issues, not to protect the coil.

I have the same wires on my car, granted they are only 2 months old and 200 miles, so far no issues. Firstly they were too long, so I ended up modifying them to shorten them up, some even 8 inches. Google how if you want a nice fit. Secondly, they fit into the heatshields just fine, if you notice you slide the shield into the engine first, it bottoms out, then push the boot into the shield and you will feel a click when it engages. I did not test resistance, because i replaced the autozone wires I bought years ago, those were junk. Everybody has theories on plugs and wires. I prefer ngk v power plugs, side gapped, no platinum or Iridium, the car is too old for that stuff, and a nice wires, no race wires because if they fail I'm gonna throw them away. Had msd wires on a few cars that were garbage as well, not the kind you build either, full made kits.

quote Originally posted by pmbrunelle: Can't you tabulate your results in Ohms/inch?

Yep.

Distributor Wire, 16" = 230 ohms (14.4 ohms / inch)
Plug Wire 25" = 330 ohms (13.2 ohms / inch)
Plug Wire 28" = 380 ohms (13.6 ohms / inch)
Plug Wire 28" = 1.18 Kohms (42 ohms / inch)
Plug Wire 29" = 400 ohms (13.8 ohms / inch)
Plug Wire 30" = 6.03 Kohms (201 ohms / inch)
Plug Wire 34" = 1.30 Kohms (38.2 ohms / inch)

Older Shelf set:

Distributor Wire 16" = 5.28 Kohms (330 ohms / inch)
Plug Wire 23" = 7.7 Kohms (334 ohms / inch)
Plug Wire 27" = 8.6 Kohms (318 ohms / inch)
Plug Wire 27" = 10.10 Kohms (374 ohms / inch)
Plug Wire 27" = 9.16 Kohms (339 ohms / inch)
Plug Wire 29" = 9.46 Kohms (326 ohms / inch)
Plug Wire 33" = 10.08 Kohms (305 ohms / inch)

Seems like the local auto store wires (older set) has less of a spread, and they are all much closer together for resistance. I think I will use them instead of the "Blue Streak" set. I would like to get a red colored set later to match the factory ones I am replacing.

quote Originally posted by computer_engineer: At the very least I may contact the seller (Rock Auto) and the manufacturer, just to let them know about the boots not fitting and the large variability in the resistance.

Did you try inserting the boots into the sleeves with the "paper" liners removed?

In regards to the resistance, although your readings are all over the place, they're probably still within specs. Charts showing wire lengths and acceptable readings are posted online.

[This message has been edited by Patrick (edited 09-21-2017).]

Exact PN of wires?

DC ohms does not matter for ignition secondary volts. "short" as to why, see https://www.magnecor.com/ click Brief Overview and Truth about plug wires.
For full answer need a High Volt Electrical Engineer to explain Skin Effect and EMI/RFI issues for HV High Frequency AC and Short duration Pulse circuits.

Many "helicoil" centers often have crap joints and will read high w/ DC ohm meter. If you get "low resistant" wires they are defective w/ high DC ohms.

Blue Streak recent catalog only list 8.5mm wires for most to all old cars, not just Fiero, but made others in the past. If not in 2014 and latter catalogs then is a NOS part and can sit in store inventory etc for decades.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

quote Originally posted by Patrick: Did you try inserting the boots into the sleeves with the "paper" liners removed? In regards to the resistance, although your readings are all over the place, they're probably still within specs. Charts showing wire lengths and acceptable readings are posted online.

I will try re-fitting the factory heat shields with the paper liners out. Didn't think about removing them. Thought they were in there for a reason, and not "optional".

quote Originally posted by theogre: Exact PN of wires? DC ohms does not matter for ignition secondary volts. "short" as to why, see https://www.magnecor.com/ click Brief Overview and Truth about plug wires. For full answer need a High Volt Electrical Engineer to explain Skin Effect and EMI/RFI issues for HV High Frequency AC and Short duration Pulse circuits. Many "helicoil" centers often have crap joints and will read high w/ DC ohm meter. If you get "low resistant" wires they are defective w/ high DC ohms. Blue Streak recent catalog only list 8.5mm wires for most to all old cars, not just Fiero, but made others in the past. If not in 2014 and latter catalogs then is a NOS part and can sit in store inventory etc for decades.

You always post that magnacore crap, when spark plug wires come into question.
I run Jacobs Electronic wires, (no longer in bussiness, as Mr, Gasket bought them up with alot of other companies) But Jacobs made the best wires ever made. Magancore says that other brands don't suppress EFI EMI, but Jacobs completely eliminated all my radio noise, with only 50 ohms in a 6ft strand. 1 ohm cuts current in half, so resistance DOES matter, contrary to what magnacore publishes. High ohm wires WILL leak spark every chance they get. Now with Jacobs gone I tell people to buy Taylor wires, low ohm, no radio noise, and they DO help the weak a$$ GM coil in the upper RPMs. I don't know about other brands, they could be/probably are crap.
But I wouldn't run magnacore if you gave me a set, like most wires on the market. Dr. Jacobs was an ignition genius and he is the one who invented the spiral core wires, everyone else is a copy cat.