Plug Wires

[sneitzel]

I got my car back from the shop today and the culpret of my hesitation/loss of power etc. was a bad plug wire on the #8 cylinder. The wire had 4X the resistance than what it should. These are the new MSD 8.5mm wires I just replaced less than 6 months ago. The shop guy told me he's had quite a few people have problems with MSD wires. Anyone else have this problem with MSD? They are going to send me a replacement since they're still under warranty but I've lost some confidence in them.

What wires does everyone else use? This car is my daily driver, mildly modified as below and does not go to the track.

Thanks.
Scott

[Joe K. 99 Zeee!!]

MSD and Taylor are supposed to have a good reputation. I'm running MSD wires myself with no noticable problems. Maybe you just got "lucky".

[raroZ28]

MSD 8.5's, 10k, no prob's.

[Injuneer]

I've been running the MSD 8.5's since the stroker was built 6 years ago. MSD is the "wire of choice" with the shop that built my engine.

[Joe 1320]

The shop guy told me he's had quite a few people have problems with MSD wires.

Spoken by a shop that probably makes their best money on a different brand. That is the language of choice when they try to sell you something different. MSD makes great products, but even they aren't immune to occational failed parts. Their quality it top notch.

[Black97]

Dumb question here. How is the restistance measured on a plug wire?

On anything electrically I work on you would want the insulation resistance to be high. That will ensure it will not arc across or even go to ground where it's not supposed to.

Isn't that the case with the wires too?

[sneitzel]

Spoken by a shop that probably makes their best money on a different brand. That is the language of choice when they try to sell you something different. MSD makes great products, but even they aren't immune to occational failed parts. Their quality it top notch.

I would normally agree with you except this shop made no attempt to sell me a brand new set of wires. In fact they replaced the bad one with an old "test wire" they had around the shop to fix the problem until I can get a replacement from MSD and only charged me for a basic diagnostic.

[fastTa]

I would normally agree with you except this shop made no attempt to sell me a brand new set of wires. In fact they replaced the bad one with an old "test wire" they had around the shop to fix the problem until I can get a replacement from MSD and only charged me for a basic diagnostic.

The thing that most people don't realize is that the actual wire running through the middle of the spark plug wires isn't much thicker than a hair off your head(as long as you are not Wolfman).

Even the best quality wires are subject to failure in either the actual wire or the surrounding insulation due heat and other uncontrollable situations.

[Joe 1320]

Dumb question here. How is the restistance measured on a plug wire?

On anything electrically I work on you would want the insulation resistance to be high. That will ensure it will not arc across or even go to ground where it's not supposed to.

Isn't that the case with the wires too?

With a digital volt meter, set to read resistance in ohms. The plug wire is removed, the test probes are put at each end and the resistance of the the wire's conductive core is read.

[fastTa]

Dumb question here. How is the restistance measured on a plug wire?

On anything electrically I work on you would want the insulation resistance to be high. That will ensure it will not arc across or even go to ground where it's not supposed to.

Isn't that the case with the wires too?

The resistance or continuity of the wire itself is what you will find everybody talking about.... but is merely only a part of the actual performance of the plug wire.

The vast majority of people do not truly understand the complexity of the laws of electricity. Today's ignition coils in street cars are exceeding 50k-55k volts. With that much potential, the pulse charge from the coil does not flow through the entire the length of fine wire used in the commonly advertised and used spiral conductor type plug wire. The pulse charge flows in a magnetic field surrounding the outer surface of the spirally wound wire. In the electrical world this is referred to as the skin effect. The skin effect causes the effective resistance of the conductor to increase in accordance with the frequency of the current.

Usually spark plug wire manufacturers will advertise their resistance ratings in ohms per foot. For example, MSD, claims 40-50 ohms per foot. I've measured MSD wires and their claims are usually on the money, but there is of course always that stray wire in the bunch.

Factory wires will usually measure anywhere between 3,000-7,000 ohms per foot.

You can also perform a voltage drop test across the plug wire, but a voltage drop test will be directly related to and dependant upon the resistance and the skin effect characteristics of a particular wire. Really the only way to properly test a wire is to do so under the same conditions as the wire would see on a certain car. Meaning you would have to have working voltage going through the wire.

Measuring the plug wire's resistance with a multimeter only applies a relatively small amount of voltage in order to measure resistance, so a multimeter cannot accurately reproduce the conditions that the plug wire are under during actual operation,......BUT it does provide a good indication of the condition of the plug wire if taken for what it is.

[HottestZ28]

I would normally agree with you except this shop made no attempt to sell me a brand new set of wires.

maybe thats because they didn't want to "tune-up" an LT1?
I am running MSD for 10k with no problem, but used plat. +4 and then changed with less then 4,000 on them.

[sneitzel]

maybe thats because they didn't want to "tune-up" an LT1?

Or because I told them when I dropped the car off it had just had a tune-up.

Approx. 6 months ago I replaced plugs (except for #2), wires and coil
About 1 month ago I had to replace the water pump and decided since I was already there and had everything apart I'd do the cap and coil on the Opti (and finally could reach plug #2). It was after that fun weekend I started having problems.

Also, they took the time to resistance check all 8 wires to find one that was bad and still only charged me for a basic diagnostic. I don't think they would have had a problem "tuning-up" an LT1 if it needed it.